Organic compound

Some chemical authorities define anorganic compoundas achemical compoundthat contains acarbon–hydrogenorcarbon–carbon bond;others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-containing compounds such asalkanes(e.g.methaneCH₄) and its derivatives are universally considered organic, but many others are sometimes considered inorganic, such ashalidesof carbon withoutcarbon-hydrogenandcarbon-carbon bonds(e.g.carbon tetrachlorideCCl₄), and certain compounds of carbon withnitrogenandoxygen(e.g.cyanideionCN⁻,hydrogen cyanideHCN,chloroformic acidClCO₂H,carbon dioxideCO₂,andcarbonateionCO2−3).

Methane(CH₄) is among the simplest organic compounds.

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 saltsandcyanide salts), along with a few other exceptions (e.g.,carbon dioxide,and evenhydrogen cyanidedespite the fact it contains a carbon-hydrogen bond), are generally consideredinorganic.Other than those just named, little consensus exists amongchemistson precisely which carbon-containing compounds are excluded, making any rigorous definition of an organic compound elusive.

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 (the carbon cycle) that begins with the conversion of carbon dioxide and a hydrogen source likewaterintosimple sugarsand other organicmoleculesbyautotrophic organismsusing light (photosynthesis) or other sources of energy. Most synthetically-produced organic compounds are ultimately derived frompetrochemicalsconsisting mainly ofhydrocarbons,which are themselves formed from the high pressure and temperature degradation of organic matter underground over geological timescales.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 anymonovalentsubstituentwhose open valence is on a carbon atom.

Definition

For historical reasons discussed below, a few types of carbon-containing compounds, such ascarbides,carbonates(excludingcarbonate esters), simpleoxides of carbon(for example,COandCO₂) andcyanidesare generally consideredinorganic compounds.Different forms (allotropes) of pure carbon, such asdiamond,graphite,fullerenesandcarbon nanotubesare also excluded because they are simple substances composed of a single element and so not generally consideredchemical compounds.The word "organic" in this context does not mean "natural".

History

Vitalism

Main article:Vitalism

Vitalismwas a widespread conception that substances found in organic nature are formed from the chemical elements by the action of a "vital force"or "life-force" (vis vitalis) that only living organisms possess.

In the 1810s,Jöns Jacob Berzeliusargued 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).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.

Vitalism survived for a short period after the formulation of modern ideas about theatomic theoryandchemical elements.It first came under question in 1824, whenFriedrich Wöhlersynthesizedoxalic acid,a compound known to occur only in living organisms, fromcyanogen.A further experiment wasWöhler's 1828 synthesisofureafrom the inorganicsaltspotassium cyanateandammonium 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.

Modern classification and ambiguities

TheL-isoleucinemolecule,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 betweenorganicandinorganiccompounds. The modern meaning oforganic compoundis 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 termcarbogenichas been proposed byE. J. Coreyas a modern alternative toorganic,but this neologism remains relatively obscure.

The organic compoundL-isoleucinemolecule presents some features typical of organic compounds:carbon–carbon bonds,carbon–hydrogen bonds,as well as covalent bonds from carbon to oxygen and to nitrogen.

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 ofalloysthat contain carbon, includingsteel(which containscementite,Fe₃C), as well as other metal and semimetal carbides (including "ionic" carbides, e.g,Al₄C₃andCaC₂and "covalent" carbides, e.g.B₄CandSiC,and graphite intercalation compounds, e.g.KC₈). Other compounds and materials that are considered 'inorganic' by most authorities include: metalcarbonates,simpleoxidesof carbon (CO,CO₂,and arguably,C₃O₂), theallotropesof carbon,cyanidederivatives not containing an organic residue (e.g.,KCN,(CN)₂,BrCN,cyanateanionOCN⁻,etc.), and heavier analogs thereof (e.g.,cyaphideanionCP⁻,CSe₂,COS;althoughcarbon disulfideCS₂is often classed as anorganicsolvent). Halides of carbon without hydrogen (e.g.,CF₄andCClF₃),phosgene(COCl₂),carboranes,metal carbonyls(e.g.,nickel tetracarbonyl),mellitic anhydride(C₁₂O₉), and other exoticoxocarbonsare also considered inorganic by some authorities.

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 compoundas it satisfies the broad definition thatorganometallic chemistrycovers 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,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.

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)₂noroxalic acid(COOH)₂are organic by this definition, yet they were two key compounds in the vitalism debate. However, theIUPAC Blue Bookon organic nomenclature specifically mentions ureaand oxalic acidas 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 inMartiansoil.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,CF₄andCCl₄would be considered by this rule to be "inorganic", whereasCHF₃,CHCl₃,andC₂Cl₆would be organic, though these compounds share many physical and chemical properties.

Classification

Main article:Organic chemistry § compounds

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.

Another distinction, based on the size of organic compounds, distinguishes betweensmall moleculesandpolymers.

Natural compounds

Natural compoundsrefer 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,somealkaloidsandterpenoids,certain nutrients such asvitamin B₁₂,and, in general, those natural products with large orstereoisometricallycomplicated molecules present in reasonable concentrations in living organisms.

Further compounds of prime importance inbiochemistryareantigens,carbohydrates,enzymes,hormones,lipidsandfatty acids,neurotransmitters,nucleic acids,proteins,peptidesandamino acids,lectins,vitamins,andfats and oils.

Synthetic compounds

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.

Mostpolymers(a category that includes allplasticsandrubbers) are organic synthetic or semi-synthetic compounds.

Biotechnology

Many organic compounds—two examples areethanolandinsulin—are manufactured industrially using organisms such as bacteria and yeast.Typically, theDNAof an organism is altered to express compounds not ordinarily produced by the organism. Many suchbiotechnology-engineered compounds did not previously exist in nature.

Databases

• TheCASdatabase is the most comprehensive repository for data on organic compounds. The search toolSciFinderis offered.
• TheBeilstein databasecontains 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.
• PubChemcontains 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.

Structure determination

Main article:Structure determination

The main tools areprotonandcarbon-13NMR spectroscopy,IR Spectroscopy,Mass spectrometry,UV/Vis SpectroscopyandX-ray crystallography.

See also

• Inorganic compound– Chemical compound without any carbon-hydrogen bonds
• List of chemical compounds
• List of organic compounds
• Organometallic chemistry– Study of organic compounds containing metal(s)

External links

• Organic Compounds Database
• Organic Materials Database