Due to carbon's ability tocatenate (form chains with other carbonatoms), millions of organic compounds are known. The study of the properties, reactions, and syntheses of organic compounds comprise the discipline known asorganic chemistry. For historical reasons, a few classes of carbon-containing compounds (e.g.,carbonate salts and cyanide salts), along with a few other exceptions (e.g.,carbon dioxide, and even hydrogen cyanide despite the fact it contains a carbon-hydrogen bond), are generally consideredinorganic. Other than those just named, little consensus exists amongchemists on precisely which carbon-containing compounds are excluded, making any rigorous definition of an organic compound elusive.[1]
Although organic compounds make up only a small percentage ofEarth's crust, they are of central importance because all known life is based on organic compounds. Living things incorporate inorganic carbon compounds into organic compounds through a network of processes (thecarbon cycle) that begins with the conversion of carbon dioxide and a hydrogen source likewater intosimple sugars and other organicmolecules byautotrophic organisms using light (photosynthesis) or other sources of energy. Most synthetically-produced organic compounds are ultimately derived frompetrochemicals consisting mainly ofhydrocarbons, which are themselves formed from the high pressure and temperature degradation of organic matter underground over geological timescales.[2] This ultimate derivation notwithstanding, organic compounds are no longer defined as compounds originating in living things, as they were historically.
In chemical nomenclature, anorganyl group, frequently represented by the letter R, refers to anymonovalentsubstituent whose open valence is on a carbon atom.[3]
Vitalism was a widespread conception that substances found in organic nature are formed from the chemical elements by the action of a "vital force"[6] or "life-force" (vis vitalis) that only living organisms possess.[7]
In the 1810s,Jöns Jacob Berzelius argued that a regulative force must exist within living bodies. Berzelius also contended that compounds could be distinguished by whether they required any organisms in theirsynthesis (organic compounds) or whether they did not (inorganic compounds).[8] Vitalism taught that formation of these "organic" compounds were fundamentally different from the "inorganic" compounds that could be obtained from the elements by chemical manipulations in laboratories.[9][10]
Vitalism survived for a short period after the formulation of modern ideas about theatomic theory andchemical elements. It first came under question in 1824, whenFriedrich Wöhler synthesizedoxalic acid, a compound known to occur only in living organisms, fromcyanogen. A further experiment wasWöhler's 1828 synthesis ofurea from the inorganicsaltspotassium cyanate andammonium sulfate. Urea had long been considered an "organic" compound, as it was known to occur only in the urine of living organisms. Wöhler's experiments were followed by many others, in which increasingly complex "organic" substances were produced from "inorganic" ones without the involvement of any living organism, thus disproving vitalism.[11]
TheL-isoleucine molecule,C6H13NO2, showing features typical of organic compounds. Carbon atoms are in black, hydrogens gray, oxygens red, and nitrogen blue.
Although vitalism has been discredited, scientific nomenclature retains the distinction betweenorganic andinorganic compounds. The modern meaning oforganic compound is any compound that contains a significant amount of carbon—even though many of the organic compounds known today have no connection to any substance found in living organisms. The termcarbogenic has been proposed byE. J. Corey as a modern alternative toorganic, but this neologism remains relatively obscure.[citation needed]
As described in detail below, any definition of organic compound that uses simple, broadly-applicable criteria turns out to be unsatisfactory, to varying degrees. The modern, commonly accepted definition of organic compound essentially amounts to any carbon-containing compound, excluding several classes of substances traditionally considered "inorganic". The list of substances so excluded varies from author to author. Still, it is generally agreed upon that there are (at least) a few carbon-containing compounds that should not be considered organic. For instance, almost all authorities would require the exclusion ofalloys that contain carbon, includingsteel (which containscementite,Fe3C), as well as other metal and semimetal carbides (including "ionic" carbides, e.g,Al4C3 andCaC2 and "covalent" carbides, e.g.B4C andSiC, and graphite intercalation compounds, e.g.KC8). Other compounds and materials that are considered 'inorganic' by most authorities include: metalcarbonates, simpleoxides of carbon (CO,CO2, and arguably,C3O2), theallotropes of carbon,cyanide derivatives not containing an organic residue (e.g.,KCN,(CN)2,BrCN,cyanate anionOCN−, etc.), and heavier analogs thereof (e.g.,cyaphide anionCP−,CSe2,COS; althoughcarbon disulfideCS2 is often classed as anorganic solvent). Halides of carbon without hydrogen (e.g.,CF4 andCClF3),phosgene (COCl2),carboranes,metal carbonyls (e.g.,nickel tetracarbonyl),mellitic anhydride (C12O9), and other exoticoxocarbons are also considered inorganic by some authorities.[citation needed]
Nickel tetracarbonyl (Ni(CO)4) and other metal carbonyls are often volatile liquids, like many organic compounds, yet they contain only carbon bonded to a transition metal and to oxygen, and are often prepared directly from metal andcarbon monoxide. Nickel tetracarbonyl is typically classified as anorganometallic compound as it satisfies the broad definition thatorganometallic chemistry covers all compounds that contain at least one carbon to metal covalent bond; it is unknown whether organometallic compounds form a subset of organic compounds. For example, the evidence of covalent Fe-C bonding incementite,[12] a major component of steel, places it within this broad definition of organometallic, yet steel and other carbon-containing alloys are seldom regarded as organic compounds. Thus, it is unclear whether the definition of organometallic should be narrowed, whether these considerations imply that organometallic compounds are not necessarily organic, or both.[citation needed]
Metal complexes with organic ligands but no carbon-metal bonds (e.g.,(CH3CO2)2Cu) are not considered organometallic; instead, they are calledmetal-organic compounds (and might be considered organic).
The relatively narrow definition of organic compounds as those containing C-H bonds excludes compounds that are (historically and practically) considered organic. NeitherureaCO(NH2)2 noroxalic acid(COOH)2 are organic by this definition, yet they were two key compounds in the vitalism debate. However, theIUPAC Blue Book on organic nomenclature specifically mentions urea[13] and oxalic acid[14] as organic compounds. Other compounds lacking C-H bonds but traditionally considered organic includebenzenehexol,mesoxalic acid, andcarbon tetrachloride.Mellitic acid, which contains no C-H bonds, is considered a possible organic compound inMartian soil.[15] Terrestrially, it, and its anhydride,mellitic anhydride, are associated with the mineralmellite (Al2C6(COO)6·16H2O).
A slightly broader definition of the organic compound includes all compounds bearing C-H or C-C bonds. This would still exclude urea. Moreover, this definition still leads to somewhat arbitrary divisions in sets of carbon-halogen compounds. For example,CF4 andCCl4 would be considered by this rule to be "inorganic", whereasCHF3,CHCl3, andC2Cl6 would be organic, though these compounds share many physical and chemical properties.[citation needed]
Organic compounds may be classified in a variety of ways. One major distinction is between natural and synthetic compounds. Organic compounds can also be classified or subdivided by the presence ofheteroatoms, e.g.,organometallic compounds, which feature bonds between carbon and ametal, andorganophosphorus compounds, which feature bonds between carbon and aphosphorus.[citation needed]
Another distinction, based on the size of organic compounds, distinguishes betweensmall molecules andpolymers.
Natural compounds refer to those that are produced by plants or animals. Many of these are still extracted from natural sources because they would be more expensive to produce artificially. Examples include mostsugars, somealkaloids andterpenoids, certain nutrients such asvitamin B12, and, in general, those natural products with large orstereoisometrically complicated molecules present in reasonable concentrations in living organisms.
Compounds that are prepared by reaction of other compounds are known as "synthetic". They may be either compounds that are already found in plants/animals or those artificial compounds that do notoccur naturally.[citation needed]
Mostpolymers (a category that includes allplastics andrubbers) are organic synthetic or semi-synthetic compounds.
Many organic compounds—two examples areethanol andinsulin—are manufactured industrially using organisms such as bacteria and yeast.[16] Typically, theDNA of an organism is altered to express compounds not ordinarily produced by the organism. Many suchbiotechnology-engineered compounds did not previously exist in nature.[17]
TheCAS database is the most comprehensive repository for data on organic compounds. The search toolSciFinder is offered.
TheBeilstein database contains information on 9.8 million substances, covers the scientific literature from 1771 to the present, and is today accessible viaReaxys. Structures and a large diversity of physical and chemical properties are available for each substance, with reference to original literature.
PubChem contains 18.4 million entries on compounds and especially covers the field ofmedicinal chemistry.
A great number of more specialized databases exist for diverse branches of organic chemistry.[18]
^Fullerenederivatives are more frequently considered organic, andfullerene chemistry is usually considered a branch of organic chemistry. The methods of organic synthesis have been applied to the rational synthesis of fullerenes and carbon nanotubes.
^Durland, Justin; Ahmadian-Moghadam, Hamid (2022),"Genetics, Mutagenesis",StatPearls, Treasure Island (FL): StatPearls Publishing,PMID32809354,archived from the original on 2023-07-09, retrieved2023-01-04
^Ernö Pretsch, Philippe Bühlmann, Martin Badertscher (2009),Structure Determination of Organic Compounds (Fourth, Revised and Enlarged Edition). Springer-Verlag Berlin Heidelberg
