Unconscious mind

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https://en.wikipedia.org/wiki/Unconscious_mind 

In psychoanalysis and other psychological theories, the unconscious mind (or the unconscious) is the part of the psyche that is not available to introspection. Although these processes exist beneath the surface of conscious awareness, they are thought to exert an effect on conscious thought processes and behavior. The term was coined by the 18th-century German Romantic philosopher Friedrich Schelling and later introduced into English by the poet and essayist Samuel Taylor Coleridge.

The emergence of the concept of the unconscious in psychology and general culture was mainly due to the work of Austrian neurologist and psychoanalyst Sigmund Freud. In psychoanalytic theory, the unconscious mind consists of ideas and drives that have been subject to the mechanism of repression: anxiety-producing impulses in childhood are barred from consciousness, but do not cease to exist, and exert a constant pressure in the direction of consciousness. However, the content of the unconscious is only knowable to consciousness through its representation in a disguised or distorted form, by way of dreams and neurotic symptoms, as well as in slips of the tongue and jokes. The psychoanalyst seeks to interpret these conscious manifestations in order to understand the nature of the repressed.

The unconscious mind can be seen as the source of dreams and automatic thoughts (those that appear without any apparent cause), the repository of forgotten memories (that may still be accessible to consciousness at some later time), and the locus of implicit knowledge (the things that we have learned so well that we do them without thinking). Phenomena related to semi-consciousness include awakening, implicit memory, subliminal messages, trances, hypnagogia and hypnosis. While sleep, sleepwalking, dreaming, delirium and comas may signal the presence of unconscious processes, these processes are seen as symptoms rather than the unconscious mind itself.

Some critics have doubted the existence of the unconscious altogether.

Historical overview

German

The term "unconscious" (German: unbewusst) was coined by the 18th-century German Romantic philosopher Friedrich Schelling (in his System of Transcendental Idealism, ch. 6, § 3) and later introduced into English by the poet and essayist Samuel Taylor Coleridge (in his Biographia Literaria). Some rare earlier instances of the term "unconsciousness" (Unbewußtseyn) can be found in the work of the 18th-century German physician and philosopher Ernst Platner.

Vedas

Influences on thinking that originate from outside an individual's consciousness were reflected in the ancient ideas of temptation, divine inspiration, and the predominant role of the gods in affecting motives and actions. The idea of internalised unconscious processes in the mind was present in antiquity, and has been explored across a wide variety of cultures. Unconscious aspects of mentality were referred to between 2,500 and 600 BC in the Hindu texts known as the Vedas, found today in Ayurvedic medicine.

Paracelsus

Paracelsus is credited as the first to make mention of an unconscious aspect of cognition in his work Von den Krankheiten (translates as "About illnesses", 1567), and his clinical methodology created a cogent system that is regarded by some as the beginning of modern scientific psychology.

Shakespeare

William Shakespeare explored the role of the unconscious in many of his plays, without naming it as such.

Philosophy

In his work Anthropology from a Pragmatic Point of View, philosopher Immanuel Kant was one of the first to discuss the subject of unconscious ideas.

Western philosophers such as Arthur Schopenhauer, Baruch Spinoza, Gottfried Wilhelm Leibniz, Johann Gottlieb Fichte, Georg Wilhelm Friedrich Hegel, Karl Robert Eduard von Hartmann, Carl Gustav Carus, Søren Aabye Kierkegaard, Friedrich Wilhelm Nietzsche and Thomas Carlyle used the word unconscious.

In 1880 at the University of Paris, Edmond Colsenet defended a philosophy thesis (PhD) on the unconscious. Élie Rabier and Alfred Fouillée performed syntheses of the unconscious "at a time when Freud was not interested in the concept".

Psychology

Nineteenth century

According to historian of psychology Mark Altschule, "It is difficult—or perhaps impossible—to find a nineteenth-century psychologist or psychiatrist who did not recognize unconscious cerebration as not only real but of the highest importance." In 1890, when psychoanalysis was still unheard of, William James, in his monumental treatise on psychology (The Principles of Psychology), examined the way Schopenhauer, von Hartmann, Janet, Binet and others had used the term 'unconscious' and 'subconscious.'" German psychologists, Gustav Fechner and Wilhelm Wundt, had begun to use the term in their experimental psychology, in the context of manifold, jumbled sense data that the mind organizes at an unconscious level before revealing it as a cogent totality in conscious form." Eduard von Hartmann published a book dedicated to the topic, Philosophy of the Unconscious, in 1869.

Freud

The iceberg metaphor proposed by G. T. Fechner is often used to provide a visual representation of Freud's theory that most of the human mind operates unconsciously.

Sigmund Freud and his followers developed an account of the unconscious mind. He worked with the unconscious mind to develop an explanation for mental illness.

For Freud, the unconscious is not merely that which is not conscious. He refers to that as the descriptive unconscious and it is only the starting postulate for real investigation into the psyche. He further distinguishes the unconscious from the pre-conscious: the pre-conscious is merely latent – thoughts, memories, etc. that are not present to consciousness but are capable of becoming so; the unconscious consists of psychic material that is made completely inaccessible to consciousness by the act of repression. The distinctions and inter-relationships between these three regions of the psyche—the conscious, the pre-conscious, and the unconscious—form what Freud calls the topographical model of the psyche. He later sought to respond to the perceived ambiguity of the term "unconscious" by developing what he called the structural model of the psyche, in which unconscious processes were described in terms of the id and the superego in their relation to the ego.

In the psychoanalytic view, unconscious mental processes can only be recognized through analysis of their effects in consciousness. Unconscious thoughts are not directly accessible to ordinary introspection, but they are capable of partially evading the censorship mechanism of repression in a disguised form, manifesting, for example, as dream elements or neurotic symptoms. Such symptoms are supposed to be capable of being "interpreted" during psychoanalysis, with the help of methods such as free association, dream analysis, and analysis of verbal slips and other unintentional manifestations in conscious life.

Jung

Main articles: Carl Jung and Collective unconscious

Carl Gustav Jung agreed with Freud that the unconscious is a determinant of personality, but he proposed that the unconscious be divided into two layers: the personal unconscious and the collective unconscious. The personal unconscious is a reservoir of material that was once conscious but has been forgotten or suppressed, much like Freud's notion. The collective unconscious, however, is the deepest level of the psyche, containing the accumulation of inherited psychic structures and archetypal experiences. Archetypes are not memories but energy centers or psychological functions that are apparent in the culture's use of symbols. The collective unconscious is therefore said to be inherited and to contain material of an entire species rather than of an individual. The collective unconscious is, according to Jung, "[the] whole spiritual heritage of mankind's evolution, born anew in the brain structure of every individual".

In addition to the structure of the unconscious, Jung differed from Freud in that he did not believe that sexuality was at the base of all unconscious thoughts.

Dreams

Freud

The purpose of dreams, according to Freud, is to fulfill repressed wishes while simultaneously allowing the dreamer to remain asleep. The dream is a disguised fulfillment of the wish because the unconscious desire in its raw form would disturb the sleeper and can only avoid censorship by associating itself with elements that are not subject to repression. Thus, Freud distinguished between the manifest content and latent content of the dream. The manifest content consists of the plot and elements of a dream as they appear to consciousness, particularly upon waking, as the dream is recalled. The latent content refers to the hidden or disguised meaning of the events and elements of the dream. It represents the unconscious psychic realities of the dreamer's current issues and childhood conflicts, the nature of which the analyst is seeking to understand through interpretation of the manifest content.

In Freud's theory, dreams are instigated by the events and thoughts of everyday life. In what he called the "dream-work", these events and thoughts, governed by the rules of language and the reality principle, become subject to the "primary process" of unconscious thought, which is governed by the pleasure principle, wish gratification, and the repressed sexual scenarios of childhood. The dream-work involves disguising these unconscious desires to preserve sleep. This process occurs primarily by means of what Freud called condensation and displacement. Condensation is the focusing of the energy of several ideas into one, and displacement is the surrender of one idea's energy to another, more trivial representative. The manifest content is thus thought to be a highly significant simplification of the latent content, capable of being deciphered in the analytic process, potentially allowing conscious insight into unconscious mental activity.

Neurobiological theory of dreams

Allan Hobson and colleagues developed what they called the activation-synthesis hypothesis, which proposes that dreams are simply the side effects of the neural activity in the brain that produces beta brain waves during REM sleep, which are associated with wakefulness. According to this hypothesis, neurons fire periodically during sleep in the lower brain levels and thus send random signals to the cortex. The cortex then synthesizes a dream in response to these signals, trying to make sense of why the brain is sending them. However, the hypothesis does not state that dreams are meaningless; it just downplays the role that emotional factors play in determining dreams.

Contemporary cognitive psychology

Research

There is an extensive body of research in contemporary cognitive psychology devoted to mental activity that is not mediated by conscious awareness. Most of this research on unconscious processes has been done in the academic tradition of the information processing paradigm. The cognitive tradition of research into unconscious processes does not rely on the clinical observations and theoretical bases of the psychoanalytic tradition; instead it is mostly data driven. Cognitive research reveals that individuals automatically register and acquire more information than they are consciously aware of or can consciously remember and report.

Much research has focused on the differences between conscious and unconscious perception. There is evidence that whether something is consciously perceived depends both on the incoming stimulus (bottom up strength) and on top-down mechanisms like attention. Recent research indicates that some unconsciously perceived information can become consciously accessible if there is cumulative evidence. Similarly, content that would normally be conscious can become unconscious through inattention (e.g. in the attentional blink) or through distracting stimuli like visual masking.

Unconscious processing of information about frequency

An extensive line of research conducted by Hasher and Zacks has demonstrated that individuals register information about the frequency of events automatically (outside conscious awareness and without engaging conscious information processing resources). Moreover, perceivers do this unintentionally, truly "automatically", regardless of the instructions they receive, and regardless of the information processing goals they have. The ability to unconsciously and relatively accurately tally the frequency of events appears to have little or no relation to the individual's age, education, intelligence, or personality. Thus it may represent one of the fundamental building blocks of human orientation in the environment and possibly the acquisition of procedural knowledge and experience, in general.

Criticism of the Freudian concept

The notion that the unconscious mind exists at all has been disputed.

Franz Brentano rejected the concept of the unconscious in his 1874 book Psychology from an Empirical Standpoint, although his rejection followed largely from his definitions of consciousness and unconsciousness.

Jean-Paul Sartre offers a critique of Freud's theory of the unconscious in Being and Nothingness, based on the claim that consciousness is essentially self-conscious. Sartre also argues that Freud's theory of repression is internally flawed. Philosopher Thomas Baldwin argues that Sartre's argument is based on a misunderstanding of Freud.

Erich Fromm contends that "The term 'the unconscious' is actually a mystification (even though one might use it for reasons of convenience, as I am guilty of doing in these pages). There is no such thing as the unconscious; there are only experiences of which we are aware, and others of which we are not aware, that is, of which we are unconscious. If I hate a man because I am afraid of him, and if I am aware of my hate but not of my fear, we may say that my hate is conscious and that my fear is unconscious; still my fear does not lie in that mysterious place: 'the' unconscious."

John Searle has offered a critique of the Freudian unconscious. He argues that the Freudian cases of shallow, consciously held mental states would be best characterized as 'repressed consciousness,' while the idea of more deeply unconscious mental states is more problematic. He contends that the very notion of a collection of "thoughts" that exist in a privileged region of the mind such that they are in principle never accessible to conscious awareness, is incoherent. This is not to imply that there are not "nonconscious" processes that form the basis of much of conscious life. Rather, Searle simply claims that to posit the existence of something that is like a "thought" in every way except for the fact that no one can ever be aware of it (can never, indeed, "think" it) is an incoherent concept. To speak of "something" as a "thought" either implies that it is being thought by a thinker or that it could be thought by a thinker. Processes that are not causally related to the phenomenon called thinking are more appropriately called the nonconscious processes of the brain.

Other critics of the Freudian unconscious include David Stannard, Richard Webster, Ethan Watters, Richard Ofshe, and Eric Thomas Weber.

Some scientific researchers proposed the existence of unconscious mechanisms that are very different from the Freudian ones. They speak of a "cognitive unconscious" (John Kihlstrom), an "adaptive unconscious" (Timothy Wilson), or a "dumb unconscious" (Loftus and Klinger), which executes automatic processes but lacks the complex mechanisms of repression and symbolic return of the repressed, and the "deep unconscious system" of Robert Langs.

In modern cognitive psychology, many researchers have sought to strip the notion of the unconscious from its Freudian heritage, and alternative terms such as "implicit" or "automatic" have been used. These traditions emphasize the degree to which cognitive processing happens outside the scope of cognitive awareness, and show that things we are unaware of can nonetheless influence other cognitive processes as well as behavior. Active research traditions related to the unconscious include implicit memory (for example, priming), and Pawel Lewicki's nonconscious acquisition of knowledge.

Molecular modelling

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https://en.wikipedia.org/wiki/Molecular_modelling

Modeling of ionic liquid

Molecular modelling encompasses all methods, theoretical and computational, used to model or mimic the behaviour of molecules. The methods are used in the fields of computational chemistry, drug design, computational biology and materials science to study molecular systems ranging from small chemical systems to large biological molecules and material assemblies. The simplest calculations can be performed by hand, but inevitably computers are required to perform molecular modelling of any reasonably sized system. The common feature of molecular modelling methods is the atomistic level description of the molecular systems. This may include treating atoms as the smallest individual unit (a molecular mechanics approach), or explicitly modelling protons and neutrons with its quarks, anti-quarks and gluons and electrons with its photons (a quantum chemistry approach).

Molecular mechanics

The backbone dihedral angles are included in the molecular model of a protein.

Molecular mechanics is one aspect of molecular modelling, as it involves the use of classical mechanics (Newtonian mechanics) to describe the physical basis behind the models. Molecular models typically describe atoms (nucleus and electrons collectively) as point charges with an associated mass. The interactions between neighbouring atoms are described by spring-like interactions (representing chemical bonds) and Van der Waals forces. The Lennard-Jones potential is commonly used to describe the latter. The electrostatic interactions are computed based on Coulomb's law. Atoms are assigned coordinates in Cartesian space or in internal coordinates, and can also be assigned velocities in dynamical simulations. The atomic velocities are related to the temperature of the system, a macroscopic quantity. The collective mathematical expression is termed a potential function and is related to the system internal energy (U), a thermodynamic quantity equal to the sum of potential and kinetic energies. Methods which minimize the potential energy are termed energy minimization methods (e.g., steepest descent and conjugate gradient), while methods that model the behaviour of the system with propagation of time are termed molecular dynamics.

${\displaystyle E=E_{\text{bonds}}+E_{\text{angle}}+E_{\text{dihedral}}+E_{\text{non-bonded}}}$

${\displaystyle E_{\text{non-bonded}}=E_{\text{electrostatic}}+E_{\text{van der Waals}}}$

This function, referred to as a potential function, computes the molecular potential energy as a sum of energy terms that describe the deviation of bond lengths, bond angles and torsion angles away from equilibrium values, plus terms for non-bonded pairs of atoms describing van der Waals and electrostatic interactions. The set of parameters consisting of equilibrium bond lengths, bond angles, partial charge values, force constants and van der Waals parameters are collectively termed a force field. Different implementations of molecular mechanics use different mathematical expressions and different parameters for the potential function. The common force fields in use today have been developed by using chemical theory, experimental reference data, and high level quantum calculations. The method, termed energy minimization, is used to find positions of zero gradient for all atoms, in other words, a local energy minimum. Lower energy states are more stable and are commonly investigated because of their role in chemical and biological processes. A molecular dynamics simulation, on the other hand, computes the behaviour of a system as a function of time. It involves solving Newton's laws of motion, principally the second law, ${\displaystyle \mathbf{F}=m\mathbf{a}}$. Integration of Newton's laws of motion, using different integration algorithms, leads to atomic trajectories in space and time. The force on an atom is defined as the negative gradient of the potential energy function. The energy minimization method is useful to obtain a static picture for comparing between states of similar systems, while molecular dynamics provides information about the dynamic processes with the intrinsic inclusion of temperature effects.

Variables

Molecules can be modelled either in vacuum, or in the presence of a solvent such as water. Simulations of systems in vacuum are referred to as gas-phase simulations, while those that include the presence of solvent molecules are referred to as explicit solvent simulations. In another type of simulation, the effect of solvent is estimated using an empirical mathematical expression; these are termed implicit solvation simulations.

Coordinate representations

Most force fields are distance-dependent, making the most convenient expression for these Cartesian coordinates. Yet the comparatively rigid nature of bonds which occur between specific atoms, and in essence, defines what is meant by the designation molecule, make an internal coordinate system the most logical representation. In some fields the IC representation (bond length, angle between bonds, and twist angle of the bond as shown in the figure) is termed the Z-matrix or torsion angle representation. Unfortunately, continuous motions in Cartesian space often require discontinuous angular branches in internal coordinates, making it relatively hard to work with force fields in the internal coordinate representation, and conversely a simple displacement of an atom in Cartesian space may not be a straight line trajectory due to the prohibitions of the interconnected bonds. Thus, it is very common for computational optimizing programs to flip back and forth between representations during their iterations. This can dominate the calculation time of the potential itself and in long chain molecules introduce cumulative numerical inaccuracy. While all conversion algorithms produce mathematically identical results, they differ in speed and numerical accuracy. Currently, the fastest and most accurate torsion to Cartesian conversion is the Natural Extension Reference Frame (NERF) method.

Applications

Molecular modelling methods are used routinely to investigate the structure, dynamics, surface properties, and thermodynamics of inorganic, biological, and polymeric systems. A large number of molecular models of force field are today readily available in databases. The types of biological activity that have been investigated using molecular modelling include protein folding, enzyme catalysis, protein stability, conformational changes associated with biomolecular function, and molecular recognition of proteins, DNA, and membrane complexes.

Lucid dream

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https://en.wikipedia.org/wiki/Lucid_dream

In the psychology subfield of oneirology, a lucid dream is a type of dream wherein the dreamer knows that they are dreaming while in their dream. The capacity to have and sustain lucid dreams is a trainable cognitive skill. During a lucid dream, the dreamer may gain some amount of volitional control over the dream characters, narrative, or environment, although this control of dream content is not the salient feature of lucid dreaming. An important distinction is that lucid dreaming is a distinct type of dream from other types of dreams such as prelucid dreams and vivid dreams, although prelucid dreams are a precursor to lucid dreams, and lucid dreams are often accompanied with enhanced dream vividness. Lucid dreams are also a distinct state from other lucid boundary sleep states such as lucid hypnagogia or lucid hypnopompia.

In formal psychology, lucid dreaming has been studied and reported for many years. Prominent figures from ancient to modern times have been fascinated by lucid dreams and have sought ways to better understand their causes and purpose. Many different theories have emerged as a result of scientific research on the subject. Further developments in psychological research have pointed to ways in which this form of dreaming may be utilized as a therapeutic technique.

The term lucid dream was coined by Dutch author and psychiatrist Frederik van Eeden in his 1913 article A Study of Dreams, though descriptions of dreamers being aware that they are dreaming predate the article. Psychologist Stephen LaBerge is widely considered the progenitor and leading pioneer of modern lucid dreaming research. He is the founder of the Lucidity Institute at Stanford University.

Definition

Paul Tholey laid the epistemological basis for the research of lucid dreams, proposing seven different conditions of clarity that a dream must fulfill to be defined as a lucid dream:

1. Awareness of the dream state (orientation)
2. Awareness of the capacity to make decisions
3. Awareness of memory functions
4. Awareness of self
5. Awareness of the dream environment
6. Awareness of the meaning of the dream
7. Awareness of concentration and focus (the subjective clarity of that state)

Later, in 1992, a study by Deirdre Barrett examined whether lucid dreams contained four "corollaries" of lucidity:

1. The dreamer is aware that they are dreaming
2. They are aware that actions will not carry over after waking
3. Physical laws need not apply in the dream
4. The dreamer has a clear memory of the waking world

Barrett found that less than a quarter of lucidity accounts exhibited all four.

Subsequently, Stephen LaBerge studied the prevalence among lucid dreams of the ability to control the dream scenario, and found that while dream control and dream awareness are correlated, neither requires the other. LaBerge found dreams that exhibit one clearly without the capacity for the other. He also found dreams where, although the dreamer is lucid and aware they could exercise control, they choose simply to observe.

History

Eastern

The practice of lucid dreaming is central to both the ancient Indian Hindu practice of Yoga nidra and the Tibetan Buddhist practice of dream Yoga. The cultivation of such awareness was a common practice among early Buddhists.

Western

Early references to the phenomenon are also found in ancient Greek writing. For example, the philosopher Aristotle wrote: "often when one is asleep, there is something in consciousness which declares that what then presents itself is but a dream." Meanwhile, the physician Galen of Pergamon used lucid dreams as a form of therapy. In addition, a letter written by Saint Augustine of Hippo in AD 415 tells the story of a dreamer, Doctor Gennadius, and refers to lucid dreaming.

Philosopher and physician Sir Thomas Browne (1605–1682) was fascinated by dreams and described his own ability to lucid dream in his Religio Medici, stating: "...yet in one dream I can compose a whole Comedy, behold the action, apprehend the jests and laugh my self awake at the conceits thereof."

Samuel Pepys, in his diary entry for 15 August 1665, records a dream, stating: "I had my Lady Castlemayne in my arms and was admitted to use all the dalliance I desired with her, and then dreamt that this could not be awake, but that it was only a dream."

Frederik van Eeden (left) and Marquis d'Hervey de Saint Denys (right), early researchers of lucid dreaming

In 1867, the French sinologist Marie-Jean-Léon, Marquis d'Hervey de Saint Denys anonymously published Les Rêves et Les Moyens de Les Diriger; Observations Pratiques ("Dreams and the ways to direct them; practical observations"), in which he describes his own experiences of lucid dreaming, and proposes that it is possible for anyone to learn to dream consciously.

In 1913, Dutch psychiatrist and writer Frederik (Willem) van Eeden (1860–1932) coined the term "lucid dream" in an article entitled "A Study of Dreams".

Some have suggested that the term is a misnomer because Van Eeden was referring to a phenomenon more specific than a lucid dream. Van Eeden intended the term lucid to denote "having insight", as in the phrase a lucid interval applied to someone in temporary remission from a psychosis, rather than as a reference to the perceptual quality of the experience, which may or may not be clear and vivid.

Skill mastery

Clinical psychologist Kristen LaMarca outlined four stages towards mastering the skill of using lucid dreaming:

Lucid Dreaming Skill Levels

Stage	Title	Description	Rarity
1	Beginner	The practitioner may have no recollection of ever having a lucid dream, and perhaps has at most experienced only brief moments of lucidity.	Common
2	Experienced	An experienced lucid dreaming practitioner wields an increased ability of dream control and capacity to execute pre-intended actions. However, there are still aspects of lucid dream practice about employing lucidity productively that are yet to be honed. One's understanding of accessing and maintaining dream lucidity deepens as one has more lucid dreams.	Less common
3	Proficient	A proficient lucid dreamer is marked by a deliberate ability to accomplish intended actions in lucid dreams, along with knowledge of the best actions for given dream scenarios. The proficient lucid dream practitioner's practice is well-planned, drawing upon a broad skill set facilitating flexible oneironautic exploration, which can include contemplative practices or athletic motor skill training. This level of skill adequacy is not necessary to develop a fulfilling lucid dream practice.	Uncommon
4	Expert	Expertise in lucid dream skill is accompanied by normalization of greater intensity of lucidity during lucid dreams. LaMarca writes that the expert's practice is "characterized by at least a decade of intense dedication, long training hours, and mentorship by other more advanced experts." Spiritual figures, such Tibetan Buddhist masters, tend to display the highest order of mastery.	Extremely rare

Progression along the skill levels is akin to a maturity in the development of the practitioner's discipline, methodology and application.

Cognitive science

In 1968, Celia Green analyzed the main characteristics of such dreams, reviewing previously published literature on the subject and incorporating new data from participants of her own. She concluded that lucid dreams were a category of experience quite distinct from ordinary dreams and said they were associated with rapid eye movement sleep (REM sleep). Green was also the first to link lucid dreams to the phenomenon of false awakenings, which has since been corroborated by more recent studies.

In 1973, the National Institute of Mental Health reported that researchers at the University of California, San Francisco, were able to train sleeping subjects to recognize they were in REM dreaming and indicate this by pressing micro switches on their thumbs. Using tones and mild shocks as cues, the experiments showed that the subjects were able to signal knowledge of their various sleep stages, including dreaming.

In 1975, Dr. Keith Hearne had the idea to exploit the nature of rapid eye movements (REM) to allow a dreamer to send a message directly from dreams to the waking world. Working with an experienced lucid dreamer (Alan Worsley), he eventually succeeded in recording (via the use of an electrooculogram or EOG) a pre-defined set of eye movements signaled from within Worsley's lucid dream. This occurred at around 8 am on the morning of April 12, 1975. Hearne's EOG experiment was formally recognized through publication in the journal for The Society for Psychical Research. Lucid dreaming was subsequently researched by asking dreamers to perform pre-determined physical responses while experiencing a dream, including eye movement signals.

In 1980, Stephen LaBerge at Stanford University developed such techniques as part of his doctoral dissertation. In 1985, LaBerge performed a pilot study that showed that time perception while counting during a lucid dream is about the same as during waking life. Lucid dreamers counted out ten seconds while dreaming, signaling the start and the end of the count with a pre-arranged eye signal measured with electrooculogram recording. LaBerge's results were confirmed by German researchers D. Erlacher and M. Schredl in 2004. However, these findings also demonstrate that motor activities, like performing squats, require more time in lucid dreams than in wakefulness.

In a further study by Stephen LaBerge, four subjects were compared, either singing or counting while dreaming. LaBerge found that the right hemisphere was more active during singing and the left hemisphere was more active during counting.

Neuroscientist J. Allan Hobson has hypothesized what might be occurring in the brain while lucid. The first step to lucid dreaming is recognizing that one is dreaming. This recognition might occur in the dorsolateral prefrontal cortex, which is one of the few areas deactivated during REM sleep and where working memory occurs. Once this area is activated and the recognition of dreaming occurs, the dreamer must be cautious to let the dream continue, but be conscious enough to remember that it is a dream. While maintaining this balance, the amygdala and parahippocampal cortex might be less intensely activated. To continue the intensity of the dream hallucinations, it is expected the pons and the parieto-occipital junction stay active.

Using electroencephalography (EEG) and other polysomnographical measurements, LaBerge and others have shown that lucid dreams begin in the rapid eye movement (REM) stage of sleep. LaBerge also proposes that there are higher amounts of beta-1 frequency band (13–19 Hz) brain wave activity experienced by lucid dreamers, hence there is an increased amount of activity in the parietal lobes making lucid dreaming a conscious process.

Paul Tholey, a German Gestalt psychologist and a professor of psychology and sports science, originally studied dreams in order to resolve the question of whether one dreams in colour or black and white. In his phenomenological research, he outlined an epistemological frame using critical realism. Tholey instructed his subjects to continuously suspect waking life to be a dream, in order that such a habit would manifest itself during dreams. He called this technique for inducing lucid dreams the Reflexionstechnik (reflection technique). Subjects learned to have such lucid dreams; they observed their dream content and reported it soon after awakening. Tholey could examine the cognitive abilities of dream figures. Nine trained lucid dreamers were directed to set other dream figures arithmetic and verbal tasks during lucid dreaming. Dream figures who agreed to perform the tasks proved more successful in verbal than in arithmetic tasks. Tholey discussed his scientific results with Stephen LaBerge, who has a similar approach.

A study was conducted by Stephen LaBerge and other scientists to see if it were possible to attain the ability to lucid dream through a drug. In 2018, galantamine was given to 121 patients in a double-blind, placebo-controlled trial, the only one of its kind. Some participants found as much as a 42 percent increase in their ability to lucid dream, compared to self-reports from the past six months, and ten people experienced a lucid dream for the first time. It is theorized that galantamine allows acetylcholine to build up, leading to greater recollection and awareness during dreaming.

Two-way communication

Graphical abstract of "Real-time dialogue between experimenters and dreamers during REM sleep"

Teams of cognitive scientists have established real-time two-way communication with people undergoing a lucid dream. During dreaming, they were able to consciously communicate with experimenters via eye movements or facial/speech muscle signals and comprehend complex questions and use working memory. Such interactive lucid dreaming could be a new approach for the scientific exploration of the dream state and could have applications for learning and creativity.

Alternative theories

Other researchers suggest that lucid dreaming is not a state of sleep, but of brief wakefulness, or "micro-awakening". Experiments by Stephen LaBerge used "perception of the outside world" as a criterion for wakefulness while studying lucid dreamers, and their sleep state was corroborated with physiological measurements. LaBerge's subjects experienced their lucid dream while in a state of REM, which critics felt may mean that the subjects are fully awake. J. Allen Hobson responded that lucid dreaming must be a state of both waking and dreaming.

Philosopher Norman Malcolm was a proponent of dream skepticism. He has argued against the possibility of checking the accuracy of dream reports, pointing out that "the only criterion of the truth of a statement that someone has had a certain dream is, essentially, his saying so." Yet dream reports are not the only evidence that some inner drama is being played out during REM sleep. Electromyography on speech and body muscles has demonstrated the sleeping body covertly walking, gesturing and talking while in REM.

Prevalence and frequency

In 2016, a meta-analytic study by David Saunders and colleagues on 34 lucid dreaming studies, taken from a period of 50 years, demonstrated that 55% of a pooled sample of 24,282 people claimed to have experienced lucid dreams at least once or more in their lifetime. Furthermore, for those that stated they did experience lucid dreams, approximately 23% reported to experience them on a regular basis, as often as once a month or more. In a 2004 study on lucid dream frequency and personality, a moderate correlation between nightmare frequency and frequency of lucid dreaming was demonstrated. Some lucid dreamers also reported that nightmares are a trigger for dream lucidity. Previous studies have reported that lucid dreaming is more common among adolescents than adults.

A 2015 study by Julian Mutz and Amir-Homayoun Javadi showed that people who had practiced meditation for a long time tended to have more lucid dreams. The authors claimed that "Lucid dreaming is a hybrid state of consciousness with features of both waking and dreaming" in a review they published in Neuroscience of Consciousness in 2017.

Mutz and Javadi found that during lucid dreaming, there is an increase in activity of the dorsolateral prefrontal cortex, the bilateral frontopolar prefrontal cortex, the precuneus, the inferior parietal lobules, and the supramarginal gyrus. All are brain functions related to higher cognitive functions, including working memory, planning, and self-consciousness. The researchers also found that during a lucid dream, "levels of self-determination" were similar to those that people experienced during states of wakefulness. They also found that lucid dreamers can only control limited aspects of their dream at once.

Mutz and Javadi also have stated that by studying lucid dreaming further, scientists could learn more about various types of consciousness, which happen to be less easy to separate and research at other times.

Techniques

This section needs expansion. You can help by adding missing information. (June 2026)

A 2022 meta-analysis of studies on lucid dream induction techniques identified 14 techniques and classified them as cognitive techniques, external stimuli, substance intervention, and cortical stimulation.

Suggested applications

Treating nightmares

It has been suggested that those who suffer from nightmares could benefit from the ability to be aware they are indeed dreaming. A pilot study performed in 2006 showed that lucid dreaming therapy treatment was successful in reducing nightmare frequency. This treatment consisted of exposure to the idea, mastery of the technique, and lucidity exercises. It was not clear what aspects of the treatment were responsible for the success of overcoming nightmares, though the treatment as a whole was said to be successful.

Australian psychologist Milan Colic has explored the application of principles from narrative therapy to clients' lucid dreams, to reduce the impact not only of nightmares during sleep but also depression, self-mutilation, and other problems in waking life. Colic found that therapeutic conversations could reduce the distressing content of dreams, while understandings about life—and even characters—from lucid dreams could be applied to their lives with marked therapeutic benefits.

Psychotherapists have applied lucid dreaming as a part of therapy. Studies have shown that, by inducing a lucid dream, recurrent nightmares can be alleviated. It is unclear whether this alleviation is due to lucidity or the ability to alter the dream itself. A 2006 study performed by Victor Spoormaker and Van den Bout evaluated the validity of lucid dreaming treatment (LDT) in chronic nightmare sufferers. LDT is composed of exposure, mastery and lucidity exercises. Results of lucid dreaming treatment revealed that the nightmare frequency of the treatment groups had decreased. In another study, Spoormaker, Van den Bout, and Meijer (2003) investigated lucid dreaming treatment for nightmares by testing eight subjects who received a one-hour individual session, which consisted of lucid dreaming exercises. The results of the study revealed that the nightmare frequency had decreased and the sleep quality had slightly increased.

Holzinger, Klösch, and Saletu managed a psychotherapy study under the working name of 'Cognition during dreaming—a therapeutic intervention in nightmares', which included 40 subjects, men and women, 18–50 years old, whose life quality was significantly altered by nightmares. The test subjects were administered Gestalt group therapy, and 24 of them were also taught to enter the state of lucid dreaming by Holzinger. This was purposefully taught in order to change the course of their nightmares. The subjects then reported the diminishment of their nightmare prevalence from 2–3 times a week to 2–3 times per month.

Creativity

In her book The Committee of Sleep, Deirdre Barrett describes how some experienced lucid dreamers have learned to remember specific practical goals such as artists looking for inspiration seeking a show of their own work once they become lucid or computer programmers looking for a screen with their desired code. However, most of these dreamers had many experiences of failing to recall waking objectives before gaining this level of control.

Exploring the World of Lucid Dreaming by Stephen LaBerge and Howard Rheingold (1990) discusses creativity within dreams and lucid dreams, including testimonials from a number of people who claim they have used the practice of lucid dreaming to help them solve a number of creative issues, from an aspiring parent thinking of potential baby names to a surgeon practicing surgical techniques. The authors discuss how creativity in dreams could stem from "conscious access to the contents of our unconscious minds"; access to "tacit knowledge"—the things we know but can't explain, or things we know but are unaware that we know.

The Dreams Behind the Music book by Craig Webb (2016) details lucid dreams of a number of musical artists, including how they are able not just to hear, but also compose, mix, arrange, practice, and perform music while conscious within their dreams.

Risks

Though lucid dreaming can be beneficial to a number of aspects of life, some risks have been suggested. Those struggling with certain mental illnesses could find it hard to tell the difference between reality and the lucid dream (psychosis).

A very small percentage of people may experience sleep paralysis, which can sometimes be confused with lucid dreaming. Although from the outside, both seem to be quite similar, there are a few distinct differences that can help differentiate them. A person usually experiences sleep paralysis when they partially wake up in REM atonia, a state in which said person is partially paralyzed and cannot move their limbs. When in sleep paralysis, people may also experience hallucinations. Although said hallucinations cannot cause physical damage, they may still be frightening. There are three common types of hallucinations: an intruder in the same room, a crushing feeling on one's chest or back, and a feeling of flying or levitating. About 7.6% of the general population have experienced sleep paralysis at least once. Exiting sleep paralysis to a waking state can be achieved by intently focusing on a part of the body, such as a finger, and wiggling it, then continuing the action of moving to the hand, the arm, and so on, until the person is fully awake.

Long-term risks with lucid dreaming have not been extensively studied, although many people have reported lucid dreaming for many years without any adverse effects. In 2018, researchers at the Wisconsin Institute for Sleep and Consciousness conducted a study that concluded individuals who lucid dream more frequently have a more active and well-connected prefrontal cortex.

False awakening

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/False_awakening

A false awakening is a vivid scenario in which a person dreams that they have woken up, while still actually asleep. After a false awakening, subjects often dream they are performing their daily morning routine such as showering or eating breakfast. False awakenings, particularly those in which individuals dream they have awakened from a sleep that involved dreaming, take on aspects of a double dream or a dream within a dream. A classic example in fiction is the double false awakening of the protagonist in Gogol's Portrait (1835).

Some studies have shown that false awakenings are frequently related to lucid dreaming, often transitioning into one another. The key distinction is that during a lucid dream, the dreamer recognizes they are dreaming, while in a false awakening, this awareness is absent.

Related concepts

Lucidity

A false awakening may occur following a dream or following a lucid dream (one in which the dreamer has been aware of dreaming). Particularly, if the false awakening follows a lucid dream, the false awakening may turn into a "pre-lucid dream", that is, one in which the dreamer may start to wonder if they are really awake and may or may not come to the correct conclusion. In a study by Harvard psychologist Deirdre Barrett, 2,000 dreams from 200 subjects were examined and it was found that false awakenings and lucidity were significantly more likely to occur within the same dream or within different dreams of the same night. False awakenings often preceded lucidity as a cue, but they could also follow the realization of lucidity, often losing it in the process.

False awakenings loops

Because the mind still dreams after a false awakening, there may be more than one false awakening in a single dream. Subjects may dream they wake up, eat breakfast, brush their teeth, and so on; suddenly awake again in bed (still in a dream), begin morning rituals again, awaken again, and so forth.

The philosopher Bertrand Russell claimed to have experienced "about a hundred" false awakenings in succession while coming around from a general anesthetic.

Protoconscious world

Giorgio Buzzi suggests that false awakenings may indicate the occasional re-appearing of a vestigial (or anyway anomalous) REM sleep in the context of disturbed or hyperaroused sleep (lucid dreaming, sleep paralysis, or situations of high anticipation). This peculiar form of REM sleep permits the replay of unaltered experiential memories, thus providing a unique opportunity to study how waking experiences interact with the hypothesized predictive model of the world. In particular, it could permit to catch a glimpse of the protoconscious world without the distorting effect of ordinary REM sleep.

In accordance with the proposed hypothesis, a high prevalence of false awakenings could be expected in children, whose "REM sleep machinery" might be less developed.

Gibson's hypothesis

Gibson's dream protoconsciousness theory states that false awakening is shaped on some fixed patterns depicting real activities, especially the day-to-day routine. False awakening is often associated with highly realistic environmental details of the familiar events like the day-to-day activities or autobiographic and episodic moments.

Symptoms

Realism and non-realism

Certain aspects of life may be dramatized or out of place in false awakenings. Things may seem wrong: details, like the painting on a wall, not being able to talk or difficulty reading (reportedly, reading in lucid dreams is often difficult or impossible).

Types

Celia Green suggested a distinction should be made between two types of false awakening:

Type 1

Type 1 is the more common, in which the dreamer seems to wake up, but not necessarily in realistic surroundings; that is, not in their own bedroom. A pre-lucid dream may ensue. More commonly, dreamers will believe they have awakened, and then either genuinely wake up in their own bed or "fall back asleep" in the dream.

A common false awakening is a "late for work" scenario. A person may "wake up" in a typical room, with most things looking normal, and realize they overslept and missed the start time at work or school. Clocks, if found in the dream, will show time indicating that fact. The resulting panic is often strong enough to truly awaken the dreamer (much like from a nightmare).

Another common Type 1 example of false awakening can result in bedwetting. In this scenario, the dreamer has had a false awakening and while in the state of dream has performed all the traditional behaviors that precede urinating – arising from bed, walking to the bathroom, and sitting down on the toilet or walking up to a urinal. The dreamer may then urinate and suddenly wake up to find they have wet themselves.

Type 2

The Type 2 false awakening seems to be considerably less common. Green characterized it as follows:

The subject appears to wake up in a realistic manner but to an atmosphere of suspense. ... The dreamer's surroundings may at first appear normal, and they may gradually become aware of something uncanny in the atmosphere, and perhaps of unwanted [unusual] sounds and movements, or they may "awake" immediately to a "stressed" and "stormy" atmosphere. In either case, the end result would appear to be characterized by feelings of suspense, excitement or apprehension.

Charles McCreery draws attention to the similarity between this description and the description by the German psychopathologist Karl Jaspers (1923) of the so-called "primary delusionary experience" (a general feeling that precedes more specific delusory belief). Jaspers wrote:

Patients feel uncanny and that there is something suspicious afoot. Everything gets a new meaning. The environment is somehow different—not to a gross degree—perception is unaltered in itself but there is some change which envelops everything with a subtle, pervasive and strangely uncertain light. ... Something seems in the air which the patient cannot account for, a distrustful, uncomfortable, uncanny tension invades him.

McCreery suggests this phenomenological similarity is not coincidental and results from the idea that both phenomena, the Type 2 false awakening and the primary delusionary experience, are phenomena of sleep. He suggests that the primary delusionary experience, like other phenomena of psychosis such as hallucinations and secondary or specific delusions, represents an intrusion into waking consciousness of processes associated with stage 1 sleep. It is suggested that the reason for these intrusions is that the psychotic subject is in a state of hyperarousal, a state that can lead to what Ian Oswald called "microsleeps" in waking life.

Other researchers doubt that these are clearly distinguished types, as opposed to being points on a subtle spectrum.

Experimental descriptions

The clinical and neurophysiological descriptions of false awakening are rare. One notable report by Takeuchi et al., was considered by some experts as a case of false awakening. It depicts a hypnagogic hallucination of an unpleasant and fearful feeling of presence in sleeping lab with perception of having risen from the bed. The polysomnography showed abundant trains of alpha rhythm on EEG (sometimes blocked by REMs mixed with slow eye movements and low muscle tone). Conversely, the two experiences of FA monitored here were close to regular REM sleep. Even quantitative analysis clearly shows theta waves predominantly, suggesting that these two experiences are a product of a dreaming rather than a fully conscious brain.

The clinical and neurophysiological characteristics of false awakening are

1. One does not feel paralysed.
2. One feels that the surroundings are familiar.
3. Frequently associated with anxiety.
4. The EEG shows low Alpha and beta bands but high delta and theta bands.
5. The EOG shows the presence of spontaneous REMs.

Organic chemistry

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Organic_chemistry 

 

Line-angle representation 

 

Ball-and-stick representation

Space-filling representation

 

Three representations of an organic compound, 5α-Dihydroprogesterone (5α-DHP), a steroid hormone. For molecules showing color, the carbon atoms are in black, hydrogens in gray, and oxygens in red. In the line angle representation, carbon atoms are implied at every terminus of a line and vertex of multiple lines, and hydrogen atoms are implied to fill the remaining needed valences (up to 4).

Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials (i.e. matter in its various forms that contain carbon atoms). It involves studying the structure of organic material to determine the structural formula, analyzing physical and chemical properties, and evaluating chemical reactivity to understand the behavior of organic compounds. The study of organic reactions includes the chemical synthesis of natural products, drugs, and polymers, and study of individual organic molecules in the laboratory and via theoretical (in silico) study.

The range of chemicals studied in organic chemistry includes hydrocarbons (compounds containing only carbon and hydrogen) as well as compounds based on carbon, but also containing other elements, especially oxygen, nitrogen, sulfur, phosphorus (included in many biochemicals) and the halogens. Organometallic chemistry is the study of compounds containing carbon–metal bonds.

Organic compounds form the basis of all known life and constitute the majority of known chemicals. The bonding patterns of carbon, with its valence of four—formal single, double, and triple bonds, plus structures with delocalized electrons—make the array of organic compounds structurally diverse, and their range of applications enormous. They form the basis of, or are constituents of, many commercial products including pharmaceuticals; petrochemicals and agrichemicals, and products made from them including lubricants, solvents; plastics; fuels and explosives. The study of organic chemistry overlaps organometallic chemistry and biochemistry, but also with medicinal chemistry, polymer chemistry, and materials science.

Educational aspects

Organic chemistry is typically taught at the college or university level. It is considered a very challenging course but has also been made accessible to students.

History

Main article: History of chemistry

For a chronological guide, see Timeline of biology and organic chemistry.

Friedrich Wöhler

Before the 18th century, chemists generally believed that compounds obtained from living organisms were endowed with a vital force that distinguished them from inorganic compounds. According to the concept of vitalism (vital force theory), organic matter was endowed with a "vital force". During the first half of the nineteenth century, some of the first systematic studies of organic compounds were reported. Around 1816 Michel Chevreul started a study of soaps made from various fats and alkalis. He separated the acids that, in combination with the alkali, produced the soap. Since these were all individual compounds, he demonstrated that it was possible to make a chemical change in various fats (which traditionally come from organic sources), producing new compounds, without "vital force". In 1828 Friedrich Wöhler produced the organic chemical urea (carbamide), a constituent of urine, from inorganic starting materials (the salts potassium cyanate and ammonium sulfate), in what is now called the Wöhler synthesis. Although Wöhler himself was cautious about claiming he had disproved vitalism, this was the first time a substance thought to be organic was synthesized in the laboratory without biological (organic) starting materials. The event is now generally accepted as indeed disproving the doctrine of vitalism.

After Wöhler, Justus von Liebig worked on the organization of organic chemistry, being considered one of its principal founders.

In 1856, William Henry Perkin, while trying to manufacture quinine, accidentally produced the organic dye now known as Perkin's mauve. His discovery, made widely known through its financial success, greatly increased interest in organic chemistry.

A crucial breakthrough for organic chemistry was the concept of chemical structure, developed independently in 1858 by both Friedrich August Kekulé and Archibald Scott Couper. Both researchers suggested that tetravalent carbon atoms could link to each other to form a carbon lattice, and that the detailed patterns of atomic bonding could be discerned by skillful interpretations of appropriate chemical reactions.

The era of the pharmaceutical industry began in the last decade of the 19th century when the German company, Bayer, first manufactured acetylsalicylic acid—more commonly known as aspirin. By 1910 Paul Ehrlich and his laboratory group began developing arsenic-based arsphenamine (Salvarsan) as the first effective medicinal treatment of syphilis, and thereby initiated the medical practice of chemotherapy. Ehrlich popularized the concepts of "magic bullet" drugs and of systematically improving drug therapies. His laboratory made decisive contributions to developing antiserum for diphtheria and standardizing therapeutic serums.

Cefalotin is a widely used synthetic antibiotic.

Early examples of organic reactions and applications were often found because of a combination of luck and preparation for unexpected observations. The latter half of the 19th century however witnessed systematic studies of organic compounds. The development of synthetic indigo is illustrative. The production of indigo from plant sources dropped from 19,000 tons in 1897 to 1,000 tons by 1914 thanks to the synthetic methods developed by Adolf von Baeyer. In 2002, 17,000 tons of synthetic indigo were produced from petrochemicals.

In the early part of the 20th century, polymers and enzymes were shown to be large organic molecules, and petroleum was shown to be of biological origin.

The multiple-step synthesis of complex organic compounds is called total synthesis. Total synthesis of complex natural compounds increased in complexity to glucose and terpineol. For example, cholesterol-related compounds have opened ways to synthesize complex human hormones and their modified derivatives. Since the start of the 20th century, complexity of total syntheses has been increased to include molecules of high complexity such as lysergic acid and vitamin B₁₂.

The total synthesis of vitamin B₁₂ marked a major achievement in organic chemistry.

The discovery of petroleum and the development of the petrochemical industry spurred the development of organic chemistry. Converting individual petroleum compounds into types of compounds by various chemical processes led to organic reactions enabling a broad range of industrial and commercial products including, among (many) others: plastics, synthetic rubber, organic adhesives, and various property-modifying petroleum additives and catalysts.

The majority of chemical compounds occurring in biological organisms are carbon compounds, so the association between organic chemistry and biochemistry is so close that biochemistry might be regarded as in essence a branch of organic chemistry. Although the history of biochemistry might be taken to span some four centuries, fundamental understanding of the field only began to develop in the late 19th century and the actual term biochemistry was coined around the start of 20th century. Research in the field increased throughout the twentieth century, without any indication of slackening in the rate of increase, as may be verified by inspection of abstraction and indexing services such as BIOSIS Previews and Biological Abstracts, which began in the 1920s as a single annual volume, but has grown so drastically that by the end of the 20th century it was only available to the everyday user as an online electronic database.

Characterization

Since organic compounds often exist as mixtures, a variety of techniques have also been developed to assess purity; chromatography techniques are especially important for this application, and include HPLC and gas chromatography. Traditional methods of separation include distillation, crystallization, evaporation, magnetic separation and solvent extraction.

Organic compounds were traditionally characterized by a variety of chemical tests, called "wet methods", but such tests have been largely displaced by spectroscopic or other computer-intensive methods of analysis. Listed in approximate order of utility, the chief analytical methods are:

• Nuclear magnetic resonance (NMR) spectroscopy is the most commonly used technique, often permitting the complete assignment of atom connectivity and even stereochemistry using correlation spectroscopy. The principal constituent atoms of organic chemistry – hydrogen and carbon – exist naturally with NMR-responsive isotopes, respectively ¹H and ¹³C.
• Elemental analysis: A destructive method used to determine the elemental composition of a molecule. See also mass spectrometry, below.
• Mass spectrometry indicates the molecular weight of a compound and, from the fragmentation patterns, its structure. High-resolution mass spectrometry can usually identify the exact formula of a compound and is used in place of elemental analysis. In former times, mass spectrometry was restricted to neutral molecules exhibiting some volatility, but advanced ionization techniques allow one to obtain the "mass spec" of virtually any organic compound.
• Crystallography can be useful for determining molecular geometry when a single crystal of the material is available. Highly efficient hardware and software allows a structure to be determined within hours of obtaining a suitable crystal.

Traditional spectroscopic methods such as infrared spectroscopy, optical rotation, and UV/VIS spectroscopy provide relatively nonspecific structural information but remain in use for specific applications. Refractive index and density can also be important for substance identification.

Properties

The physical properties of organic compounds typically of interest include both quantitative and qualitative features. Quantitative information includes a melting point, boiling point, solubility, and index of refraction. Qualitative properties include odor, consistency, and color.

Melting and boiling properties

Organic compounds typically melt and many boil. In contrast, while inorganic materials generally can be melted, many do not boil, and instead tend to degrade. In earlier times, the melting point (m.p.) and boiling point (b.p.) provided crucial information on the purity and identity of organic compounds. The melting and boiling points correlate with the polarity of the molecules and their molecular weight. Some organic compounds, especially symmetrical ones, sublime. A well-known example of a sublimable organic compound is para-dichlorobenzene, the odiferous constituent of modern mothballs. Organic compounds are usually not very stable at temperatures above 300 °C, although some exceptions exist.

Solubility

Neutral organic compounds tend to be hydrophobic; that is, they are less soluble in water than in organic solvents. Exceptions include organic compounds that contain ionizable groups as well as low molecular weight alcohols, amines, and carboxylic acids where hydrogen bonding occurs. Otherwise, organic compounds tend to dissolve in organic solvents. Solubility varies widely with the organic solute and with the organic solvent.

Solid state properties

Various specialized properties of molecular crystals and organic polymers with conjugated systems are of interest depending on applications, e.g. thermo-mechanical and electro-mechanical such as piezoelectricity, electrical conductivity (see conductive polymers and organic semiconductors), and electro-optical (e.g. non-linear optics) properties. For historical reasons, such properties are mainly the subjects of the areas of polymer science and materials science.

Nomenclature

Main article: IUPAC nomenclature of organic chemistry

Various names and depictions for one organic compound

The names of organic compounds are either systematic, following logically from a set of rules, or nonsystematic, following various traditions. Systematic nomenclature is stipulated by specifications from IUPAC (International Union of Pure and Applied Chemistry). Systematic nomenclature starts with the name for a parent structure within the molecule of interest. This parent name is then modified by prefixes, suffixes, and numbers to unambiguously convey the structure. Given that millions of organic compounds are known, rigorous use of systematic names can be cumbersome. Thus, IUPAC recommendations are more closely followed for simple compounds, but not complex molecules. To use the systematic naming, one must know the structures and names of the parent structures. Parent structures include unsubstituted hydrocarbons, heterocycles, and monofunctionalized derivatives thereof.

Nonsystematic nomenclature is simpler and unambiguous, at least to organic chemists. Nonsystematic names do not indicate the structure of the compound. They are common for complex molecules, which include most natural products. Thus, the informally named lysergic acid diethylamide is systematically named (6aR,9R)-N,N-diethyl-7-methyl-4,6,6a,7,8,9-hexahydroindolo-[4,3-fg] quinoline-9-carboxamide.

With the increased use of computing, other naming methods have evolved that are intended to be interpreted by machines. Two popular formats are SMILES and InChI.

Structural drawings

Organic molecules are described more commonly by drawings or structural formulas, combinations of drawings and chemical symbols. The line-angle formula is simple and unambiguous. In this system, the endpoints and intersections of each line represent one carbon, and hydrogen atoms can either be notated explicitly or assumed to be present as implied by tetravalent carbon.

This diagram shows 5 distinct structural representations of the organic compound butane. The left-most structure is a bond-line drawing where the hydrogen atoms are removed. The second structure shows the added hydrogens depicted—the dark wedged bonds indicate the hydrogen atoms are coming toward the reader, the hashed bonds indicate the atoms are oriented away from the reader, and the solid (plain) bonds indicate the bonds are in the plane of the screen/paper. The middle structure shows the four carbon atoms. The 4th structure is a representation just showing the atoms and bonds without three dimensions. The right-most structure is a condensed structure representation of butane.

History

By 1880 an explosion in the number of chemical compounds being discovered occurred, assisted by new synthetic and analytical techniques. Grignard described the situation as "chaos le plus complet" (complete chaos) due to the lack of convention, it was possible to have multiple names for the same compound. This led to the creation of the Geneva rules in 1892.

Classification of organic compounds

Functional groups

The family of carboxylic acids contains a carboxyl (-COOH) functional group. Acetic acid, shown here, is an example.

Main article: Functional group

The concept of functional groups is central in organic chemistry, both as a means to classify structures and for predicting properties. A functional group is a molecular module, and the reactivity of that functional group is assumed, within limits, to be the same in a variety of molecules. Functional groups can have a decisive influence on the chemical and physical properties of organic compounds. Molecules are classified based on their functional groups. Alcohols, for example, all have the subunit C-O-H. All alcohols tend to be somewhat hydrophilic, usually form esters, and usually can be converted to the corresponding halides. Most functional groups feature heteroatoms (atoms other than C and H). Organic compounds are classified according to functional groups, e.g., alcohols, carboxylic acids, amines, etc. Functional groups make the molecule more acidic or basic due to their electronic influence on surrounding parts of the molecule.

As the pK_a (aka basicity) of the molecular addition/functional group increases, there is a corresponding dipole, when measured, increases in strength. A dipole directed towards the functional group (higher pK_a therefore basic nature of group) points towards it and decreases in strength with increasing distance. Dipole distance (measured in Angstroms) and steric hindrance towards the functional group have an intermolecular and intramolecular effect on the surrounding environment and pH level.

Different functional groups have different pK_a values and bond strengths (single, double, triple) leading to increased electrophilicity with lower pK_a and increased nucleophile strength with higher pK_a. More basic/nucleophilic functional groups desire to attack an electrophilic functional group with a lower pK_a on another molecule (intermolecular) or within the same molecule (intramolecular). Any group with a net acidic pK_a that gets within range, such as an acyl or carbonyl group is fair game. Since the likelihood of being attacked decreases with an increase in pK_a, acyl chloride components with the lowest measured pK_a values are most likely to be attacked, followed by carboxylic acids (pK_a = 4), thiols (13), malonates (13), alcohols (17), aldehydes (20), nitriles (25), esters (25), then amines (35). Amines are very basic, and are great nucleophiles/attackers.

Aliphatic compounds

Main article: Aliphatic compound

The aliphatic hydrocarbons are subdivided into three groups of homologous series according to their state of saturation:

• alkanes (paraffins): aliphatic hydrocarbons without any double or triple bonds, i.e. just C-C, C-H single bonds
• alkenes (olefins): aliphatic hydrocarbons that contain one or more double bonds, i.e. di-olefins (dienes) or poly-olefins.
• alkynes (acetylenes): aliphatic hydrocarbons which have one or more triple bonds.

The rest of the group is classified according to the functional groups present. Such compounds can be "straight-chain", branched-chain or cyclic. The degree of branching affects characteristics, such as the octane number or cetane number in petroleum chemistry.

Both saturated (alicyclic) compounds and unsaturated compounds exist as cyclic derivatives. The most stable rings contain five or six carbon atoms, but large rings (macrocycles) and smaller rings are common. The smallest cycloalkane family is the three-membered cyclopropane ((CH₂)₃). Saturated cyclic compounds contain single bonds only, whereas aromatic rings have an alternating (or conjugated) double bond. Cycloalkanes do not contain multiple bonds, whereas the cycloalkenes and the cycloalkynes do.

Aromatic compounds

Benzene is one of the best-known aromatic compounds as it is one of the simplest and most stable aromatics.

Aromatic hydrocarbons contain conjugated double bonds. This means that every carbon atom in the ring is sp² hybridized, allowing for added stability. The most important example is benzene, the structure of which was formulated by Kekulé who first proposed the delocalization or resonance principle for explaining its structure. For "conventional" cyclic compounds, aromaticity is conferred by the presence of 4n + 2 delocalized pi electrons, where n is an integer. Particular instability (antiaromaticity) is conferred by the presence of 4n conjugated pi electrons.

Heterocyclic compounds

Main article: Heterocyclic compound

The characteristics of the cyclic hydrocarbons are again altered if heteroatoms are present, which can exist as either substituents attached externally to the ring (exocyclic) or as a member of the ring itself (endocyclic). In the case of the latter, the ring is termed a heterocycle. Pyridine and furan are examples of aromatic heterocycles while piperidine and tetrahydrofuran are the corresponding alicyclic heterocycles. The heteroatom of heterocyclic molecules is generally oxygen, sulfur, or nitrogen, with the latter being particularly common in biochemical systems.

Heterocycles are commonly found in a wide range of products including aniline dyes and medicines. Additionally, they are prevalent in a wide range of biochemical compounds such as alkaloids, vitamins, steroids, and nucleic acids (e.g. DNA, RNA).

Rings can fuse with other rings on an edge to give polycyclic compounds. The purine nucleoside bases are notable polycyclic aromatic heterocycles. Rings can also fuse on a "corner" such that one atom (almost always carbon) has two bonds going to one ring and two to another. Such compounds are termed spiro and are important in several natural products.

Polymers

Main article: Polymer

This swimming board is made of polystyrene; it is an example of a polymer.

One important property of carbon is that it readily forms chains, or networks, that are linked by carbon-carbon (carbon-to-carbon) bonds. The linking process is called polymerization, while the chains, or networks, are called polymers. The source compound is called a monomer.

Two main groups of polymers exist: synthetic polymers and biopolymers. Synthetic polymers are artificially manufactured, and are commonly referred to as industrial polymers. Biopolymers occur within a respectfully natural environment, or without human intervention.

Biomolecules

Maitotoxin, a complex organic biological toxin

Biomolecular chemistry is a major category within organic chemistry which is frequently studied by biochemists. Many complex multi-functional group molecules are important in living organisms. Some are long-chain biopolymers, and these include peptides, DNA, RNA and the polysaccharides such as starches in animals and celluloses in plants. The other main classes are amino acids (monomer building blocks of peptides and proteins), carbohydrates (which includes the polysaccharides), the nucleic acids (which include DNA and RNA as polymers), and the lipids. Besides, animal biochemistry contains many small molecule intermediates which assist in energy production through the Krebs cycle, and produces isoprene, the most common hydrocarbon in animals. Isoprenes in animals form the important steroid structural (cholesterol) and steroid hormone compounds; and in plants form terpenes, terpenoids, some alkaloids, and a class of hydrocarbons called biopolymer polyisoprenoids present in the latex of various species of plants, which is the basis for making rubber. Biologists usually classify the above-mentioned biomolecules into four main groups, i.e., proteins, lipids, carbohydrates, and nucleic acids. Petroleum and its derivatives are considered organic molecules, which is consistent with the fact that this oil comes from the fossilization of living beings, i.e., biomolecules. See also: peptide synthesis, oligonucleotide synthesis and carbohydrate synthesis.

Small molecules

Molecular models of caffeine

In pharmacology, an important group of organic compounds is small molecules, also referred to as "small organic compounds". In this context, a small molecule is a small organic compound that is biologically active but is not a polymer. In practice, small molecules have a molar mass less than approximately 1000 g/mol.

Fullerenes

Fullerenes and carbon nanotubes, carbon compounds with spheroidal and tubular structures, have stimulated much research into the related field of materials science. The first fullerene was discovered in 1985 by Sir Harold W. Kroto of the United Kingdom and by Richard E. Smalley and Robert F. Curl Jr., of the United States. Using a laser to vaporize graphite rods in an atmosphere of helium gas, these chemists and their assistants obtained cagelike molecules composed of 60 carbon atoms (C60) joined by single and double bonds to form a hollow sphere with 12 pentagonal and 20 hexagonal faces—a design that resembles a football, or soccer ball. In 1996 the trio was awarded the Nobel Prize for their pioneering efforts. The C60 molecule was named buckminsterfullerene (or, more simply, the buckyball) after the American architect R. Buckminster Fuller, whose geodesic dome is constructed on the same structural principles.

Others

Organic compounds containing bonds of carbon to nitrogen, oxygen and the halogens are not normally grouped separately. Others are sometimes put into major groups within organic chemistry and discussed under titles such as organosulfur chemistry, organometallic chemistry, organophosphorus chemistry and organosilicon chemistry.

Organic reactions

Main article: Organic reaction

Organic reactions are chemical reactions involving organic compounds. Many of these reactions are associated with functional groups. The general theory of these reactions involves careful analysis of such properties as the electron affinity of key atoms, bond strengths and steric hindrance. These factors can determine the relative stability of short-lived reactive intermediates, which usually directly determine the path of the reaction.

The basic reaction types are: addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions and redox reactions. An example of a common reaction is a substitution reaction written as:

Nu⁻ + C−X → C−Nu + X⁻

where X is some functional group and Nu is a nucleophile.

The number of possible organic reactions is infinite. However, certain general patterns are observed that can be used to describe many common or useful reactions. Each reaction has a stepwise reaction mechanism that explains how it happens in sequence—although the detailed description of steps is not always clear from a list of reactants alone.

The stepwise course of any given reaction mechanism can be represented using arrow pushing techniques in which curved arrows are used to track the movement of electrons as starting materials transition through intermediates to final products. The mechanism for certain organic reactions remain subjects of ongoing debate and have not been fully elucidated.

Organic synthesis

A synthesis designed by E.J. Corey for oseltamivir (Tamiflu). This synthesis has 11 distinct reactions.

See also: Chemical synthesis and Organic synthesis

Synthetic organic chemistry is an applied science as it borders engineering, the "design, analysis, and/or construction of works for practical purposes". Organic synthesis of a novel compound is a problem-solving task, where a synthesis is designed for a target molecule by selecting optimal reactions from optimal starting materials. Complex compounds can have tens of reaction steps that sequentially build the desired molecule. The synthesis proceeds by utilizing the reactivity of the functional groups in the molecule. For example, a carbonyl compound can be used as a nucleophile by converting it into an enolate, or as an electrophile; the combination of the two is called the aldol reaction. Designing practically useful syntheses always requires conducting the actual synthesis in the laboratory. The scientific practice of creating novel synthetic routes for complex molecules is called total synthesis.

Strategies to design a synthesis include retrosynthesis, popularized by E.J. Corey, which starts with the target molecule and splices it to pieces according to known reactions. The pieces, or the proposed precursors, receive the same treatment, until available and ideally inexpensive starting materials are reached. Then, the retrosynthesis is written in the opposite direction to give the synthesis. A "synthetic tree" can be constructed because each compound and also each precursor has multiple syntheses.