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Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation (by synthesis or by other means) of carbon-based compounds, hydrocarbons, and their derivatives. These compounds may contain any number of other elements, including hydrogen, nitrogen, oxygen, the halogens as well as phosphorus, silicon and sulfur. Organic compounds are structurally diverse. The range of application of organic compounds is enormous. They form the basis of, or are important constituents of many products (plastics, drugs, petrochemicals, food, explosives, paints, to name but a few) and, with very few exceptions, they form the basis of all earthly life processes. Organic chemistry evolved in waves of innovation. These innovations were motivated by practical considerations as well as theoretical innovations. However, like all areas of science, chemistry is underpinned financially by the very large applications in biochemistry, polymer science, pharmaceutical chemistry, and agrochemicals. Contents [hide] 1 History 2 Characterization 3 Properties 3.1 Melting and boiling properties 3.2 Solubility 3.3 Solid state properties 4 Nomenclature 4.1 Structural drawings 5 Classification of organic compounds 5.1 Functional groups 5.2 Aliphatic compounds 5.3 Aromatic compounds 5.3.1 Heterocyclic compounds 5.4 Polymers 5.5 Biomolecules 5.6 Small molecules 5.7 Fullerenes 5.8 Others 6 Organic synthesis 7 Organic reactions 8 See also 9 References 10 External links  History Main article: History of chemistry Friedrich WöhlerIn the early nineteenth century, chemists generally believed that compounds obtained from living organisms were too complex to be obtained synthetically. According to the concept of vitalism, organic matter was endowed with a "vital force". They named these compounds "organic" and directed their investigations toward inorganic materials that seemed more easily studied. During the first half of the nineteenth century, scientists realized that organic compounds can be synthesized in the laboratory. Around 1816 Michel Chevreul started a study of soaps made from various fats and alkalis. He separated the different 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 the inorganic ammonium cyanate NH4OCN, in what is now called the Wöhler synthesis. Although Wöhler was always cautious about claiming that he had thereby destroyed the theory of vital force, historians have looked to this event as the turning point. In 1856 William Henry Perkin, trying to manufacture quinine, again accidentally manufactured the organic dye now called Perkin's mauve. By generating a huge amount of money this discovery greatly increased interest in organic chemistry. The crucial breakthrough for organic chemistry was the concept of chemical structure, developed independently and simultaneously by Friedrich August Kekule and Archibald Scott Couper in 1858. Both men 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 history of organic chemistry continued with the discovery of petroleum and its separation into fractions according to boiling ranges. The conversion of different compound types or individual compounds by various chemical processes created the petroleum chemistry leading to the birth of the petrochemical industry, which successfully manufactured artificial rubbers, the various organic adhesives, the property-modifying petroleum additives, and plastics. The pharmaceutical industry began in the last decade of the 19th century when acetylsalicylic acid (more commonly referred to as aspirin) manufacture was started in Germany by Bayer. The first time a drug was systematically improved was with arsphenamine (Salvarsan). Numerous derivatives of the dangerously toxic atoxyl were examined by Paul Ehrlich and his group, and the compound with best effectiveness and toxicity characteristics was selected for production. Although early examples of organic reactions and applications were often serendipitous, the latter half of the 19th century witnessed highly systematic studies of organic compounds. Beginning in the 20th century, progress of organic chemistry allowed the synthesis of highly complex molecules via multistep procedures. Concurrently, polymers and enzymes were understood to be large organic molecules, and petroleum was shown to be of biological origin. The process of finding new synthesis routes for a given compound is called total synthesis. Total synthesis of complex natural compounds started with urea, increased in complexity to glucose and terpineol, and in 1907, total synthesis was commercialized the first time by Gustaf Komppa with camphor. Pharmaceutical benefits have been substantial, for example cholesterol-related compounds have opened ways to synthesis of complex human hormones and their modified derivatives. Since the start of the 20th century, complexity of total syntheses has been increasing, with examples such as lysergic acid and vitamin B12. Today's targets feature tens of stereogenic centers that must be synthesized correctly with asymmetric synthesis. Biochemistry, the chemistry of living organisms, their structure and interactions in vitro and inside living systems, has only started in the 20th century, opening up a new chapter of organic chemistry with enormous scope. Biochemistry, like organic chemistry, primarily focuses on compounds containing carbon as well.  Characterization Since organic compounds often exist as mixtures, a variety of techniques have also been developed to assess purity, especially important being chromatography techniques such as HPLC and gas chromatography. Traditional methods of separation include distillation, crystallization, 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 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 lieu 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 is an unambiguous method for determining molecular geometry, the proviso being that single crystals of the material must be available and the crystal must be representative of the sample. Highly automated software allows a structure to be determined within hours of obtaining a suitable crystal. Traditional spectroscopic methods such as infrared spectroscopy, optical rotation, UV/VIS spectroscopy provide relatively nonspecific structural information but remain in use for specific classes of compounds. Additional methods are described in the article on analytical chemistry.  Properties Physical properties of organic compounds typically of interest include both quantitative and qualitative features. Quantitative information include melting point, boiling point, and index of refraction. Qualitative properties include odor, solubility, and color.  Melting and boiling properties In contrast to many inorganic materials, organic compounds typically melt and many boil. 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, that is they evaporate without melting. A well known example of a sublimable organic compound is para-dichlorobenzene, the odiferous constituent of 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. Organic compounds tend to dissolve in organic solvents. Solvents can be either pure substances like ether or ethyl alcohol, or mixtures, such as the paraffinic solvents such as the various petroleum ethers and white spirits, or the range of pure or mixed aromatic solvents obtained from petroleum or tar fractions by physical separation or by chemical conversion. Solubility in the different solvents depends upon the solvent type and on the functional groups if present.  Solid state properties Various specialized properties are of interest depending on applications, e.g. thermo-mechanical and electro-mechanical such as piezoelectricity, electrical conductivity (see organic metals), 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. A metaphor is more forceful (active) than an analogy, because metaphor asserts two things are the same, whereas analogy implies a difference; other rhetorical comparative figures of speech, such as metonymy, parable, simile, and synecdoche, are species of metaphor distinguished by how the comparison is communicated. The metaphor category also contains these specialized types: allegory: An extended metaphor wherein a story illustrates an important attribute of the subject catachresis: A mixed metaphor used by design and accident (a rhetorical fault) parable: An extended metaphor narrated as an anecdote illustrating and teaching a moral lesson.  Common types A dead metaphor is one in which the sense of a transferred image is absent. Examples: "to grasp a concept" and "to gather what you've understood" use physical action as a metaphor for understanding. Most people do not visualize the action — dead metaphors normally go unnoticed. Some people distinguish between a dead metaphor and a cliché. Others use "dead metaphor" to denote both. An extended metaphor (conceit), establishes a principal subject (comparison) and subsidiary subjects (comparisons). The As You Like It quotation is a good example, the world is described as a stage, and then men and women are subsidiary subjects further described in the same context. A mixed metaphor is one that leaps from one identification to a second identification inconsistent with the first. Example: "If we can hit that bullseye then the rest of the dominoes will fall like a house of cards... Checkmate."Quote from Futurama TV show character Zapp Brannigan,  Per Hans Blumenberg’s metaphorology, absolute metaphor denotes a figure or a concept that cannot be reduced to, or replaced with solely conceptual thought and language. Absolute metaphors, e.g. “light” (for “truth”) and “seafaring” (for “human existence”) – have distinctive meanings (unlike the literal meanings), and, thereby, function as orientations in the world, and as theoretic questions, such as presenting the world as a whole. Because they exist at the pre-predicative level, express and structure pragmatic and theoretical views of Man and the World.  Uncommon types Other types of metaphor have been identified as well, though the nomenclatures are not as universally accepted: An absolute or paralogical metaphor (sometimes called an anti-metaphor) is one in which there is no discernible point of resemblance between the idea and the image. e.g. “light” as a metaphor for virtue. An active metaphor is one which by contrast to a dead metaphor, is not part of daily language and is noticeable as a metaphor. A complex metaphor is one which mounts one identification on another. Example: "That throws some light on the question." Throwing light is a metaphor: there is no actual light, and a question is not the sort of thing that can be lit up. A compound or loose metaphor is one that catches the mind with several points of similarity. Example: "He has the wild stag's foot." This phrase suggests grace and speed as well as daring. A dying metaphor is a pejorative term coined by George Orwell in his essay Politics and the English Language. Orwell defines a dying metaphor as a metaphor that isn't dead (dead metaphors are different, as they are treated like ordinary words), but has been worn out and is used because it saves people the trouble of inventing an original phrase for themselves. In short, a cliché. Example: Achilles' heel. Orwell suggests that writers scan their work for such dying forms that they have 'been seen regularly before in print' and replace them with alternative language patterns. An epic metaphor or Homeric simile is an extended metaphor containing details about the vehicle that are not, in fact, necessary for the metaphoric purpose. This can be extended to humorous lengths, for instance: "This is a crisis. A large crisis. In fact, if you've got a moment, it's a twelve-storey crisis with a magnificent entrance hall, carpeting throughout, 24-hour porterage and an enormous sign on the roof saying 'This Is a Large Crisis.'" (Blackadder) An implicit metaphor is one in which the tenor is not specified but implied. Example: "Shut your trap!" Here, the mouth of the listener is the unspecified tenor. An implied or unstated metaphor is a metaphor not explicitly stated or obvious that compares two things by using adjectives that commonly describe one thing, but are used to describe another comparing the two. An example: "Golden baked skin", comparing bakery goods to skin or "green blades of nausea", comparing green grass to the pallor of a nauseated person or "leafy golden sunset" comparing the sunset to a tree in the fall. A simple or tight metaphor is one in which there is but one point of resemblance between the tenor and the vehicle. Example: "Cool it". In this example, the vehicle, "Cool", is a temperature and nothing else, so the tenor, "it", can only be grounded to the vehicle by one attribute. A submerged metaphor is one in which the vehicle is implied, or indicated by one aspect. Example: "my winged thought". Here, the audience must supply the image of the bird. A synecdochic metaphor is a trope that is both a metaphor and a synecdoche in which a small part of something is chosen to represent the whole so as to highlight certain elements of the whole.  Use outside of rhetoric The term metaphor is also used for the following terms that are not a part of rhetoric: A cognitive metaphor is the association of an object to an experience outside the object's environment. A conceptual metaphor is an underlying association that is systematic in both language and thought. A root metaphor is the underlying worldview that shapes an individual's understanding of a situation. A therapeutic metaphor is an experience that allows one to learn about more than just that experience. A visual metaphor provides a frame or window on experience. Metaphors can also be implied and extended throughout pieces of literature.  History in literature and language Metaphor is present in the oldest written Sumerian language narrative, the Epic of Gilgamesh: My friend, the swift mule, fleet wild ass of the mountain, panther of the wilderness, after we joined together and went up into the mountain, fought the Bull of Heaven and killed it, and overwhelmed Humbaba, who lived in the Cedar Forest, now what is this sleep that has seized you? — (Trans. Kovacs, 1989) In this example, the friend is compared to a mule, a wild donkey, and a panther to indicate that the speaker sees traits from these animals in his friend (A comparison between two or more unlike objects). The idea of metaphor can be traced back to Aristotle who, in his “Poetics” (around 335 BC), defines “metaphor” as follows: “Metaphor is the application of a strange term either transferred from the genus and applied to the species or from the species and applied to the genus, or from one species to another or else by analogy.” For the sake of clarity and comprehension it might additionally be useful to quote the following two alternative translations: “Metaphor is the application of an alien name by transference either from genus to species, or from species to genus, or from species to species, or by analogy, that is, proportion.” Or, as Halliwell puts it in his translation: “Metaphor is the application of a word that belongs to another thing: either from genus to species, species to genus, species to species, or by analogy.” Therefore, the key aspect of a metaphor is a specific transference of a word from one context into another. With regard to the four kinds of metaphors which Aristotle distincts against each other the last one (transference by analogy) is the most eminent one so that all important theories on metaphor have a reference to this characterization. The plays of Sophocles, Aeschylus, and Euripides, among others, were almost invariably allegorical, showing the tragedy of the protagonists, either to caution the audience metaphorically about temptation, or to lambast famous individuals of the day by inferring similarities with the caricatures in the play. Even when they are not intentional, they can be drawn between most writing or language and other topics. In this way it can be seen that any theme in literature is a metaphor, using the story to convey information about human perception of the theme in question.  In historical linguistics In historical onomasiology or, more generally, in historical linguistics, metaphor is defined as semantic change based on similarity, i.e. a similarity in form or function between the original concept named by a word and the target concept named by this word. ex. mouse: small, gray rodent → small, gray, mouse-shaped computer device. Some recent linguistic theories view language as by its nature all metaphorical; or that language in essence is metaphorical.  Historical theories of metaphor  Metaphor as style in speech and writing Viewed as an aspect of speech and writing, metaphor qualifies as style, in particular, style characterized by a type of analogy. An expression (word, phrase) that by implication suggests the likeness of one entity to another entity gives style to an item of speech or writing, whether the entities consist of objects, events, ideas, activities, attributes, or almost anything expressible in language. For example, in the first sentence of this paragraph, the word "viewed" serves as a metaphor for "thought of", implying analogy of the process of seeing and the thought process. The phrase, "viewed as an aspect of", projects the properties of seeing (vision) something from a particular perspective onto thinking about something from a particular perspective, that "something" in this case referring to "metaphor" and that "perspective" in this case referring to the characteristics of speech and writing. As a characteristic of speech and writing, metaphors can serve the poetic imagination, enabling William Shakespeare, in his play "As You Like It", to compare the world to a stage and its human inhabitants players entering and exiting upon that stage; enabling Sylvia Plath, in her poem "Cut", to compare the blood issuing from her cut thumb to the running of a million soldiers, "redcoats, every one"; and, enabling Robert Frost, in "The Road Not Taken", to compare one´s life to a journey. Viewed also as an aspect of speech and writing, metaphor can serve as a device for persuading the listener or reader of the speaker-writer´s argument or thesis, the so-called rhetorical metaphor....  Metaphor as foundational to our conceptual system Cognitive linguists emphasize that metaphors serve to facilitate the understanding of one conceptual domain, typically an abstract one like 'life' or 'theories' or 'ideas', through expressions that relate to another, more familiar conceptual domain, typically a more concrete one like 'journey' or 'buildings' or 'food'. Food for thought: we devour a book of raw facts, try to digest them, stew over them, let them simmer on the back-burner, regurgitate them in discussions, cook up explanations, hoping they do not seem half-baked. Theories as buildings: we establish a foundation for them, a framework, support them with strong arguments, buttressing them with facts, hoping they will stand. Life as journey: some of us travel hopefully, others seem to have no direction, many lose their way. A convenient short-hand way of capturing this view of metaphor is the following: CONCEPTUAL DOMAIN (A) IS CONCEPTUAL DOMAIN (B), which is what is called a conceptual metaphor. A conceptual metaphor consists of two conceptual domains, in which one domain is understood in terms of another. A conceptual domain is any coherent organization of experience. Thus, for example, we have coherently organized knowledge about journeys that we rely on in understanding life. How does this relate to the nature and importance of our conceptual system, and to metaphor as foundational to our conceptual system?  More than just a figure of speech Some theorists have suggested that metaphors are not merely stylistic, but that they are cognitively important as well. In Metaphors We Live By George Lakoff and Mark Johnson argue that metaphors are pervasive in everyday life, not just in language, but also in thought and action. A common definition of a metaphor can be described as a comparison that shows how two things that are not alike in most ways are similar in another important way. They explain how a metaphor is simply understanding and experiencing one kind of thing in terms of another. The authors call this concept a ‘conduit metaphor.’ By this they meant that a speaker can put ideas or objects into words or containers, and then send them along a channel, or conduit, to a listener who takes that idea or object out of the container and makes meaning of it. In other words, communication is something that ideas go into. The container is separate from the ideas themselves. Lakoff and Johnson give several examples of daily metaphors we use, such as “argument is war” and “time is money.” Metaphors are widely used in context to describe personal meaning. The authors also suggest that communication can be viewed as a machine: “Communication is not what one does with the machine, but is the machine itself.” (Johnson, Lakoff, 1980).