Editing Organic compound (section)

===Modern classification and ambiguities===
[[Image:L-isoleucine-3D-balls.png|thumb|upright=0.8|The [[isoleucine|<small>L</small>-isoleucine]] molecule, {{chem2|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 between ''organic'' and ''inorganic'' compounds. The modern meaning of ''organic 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 term ''carbogenic'' has been proposed by [[E. J. Corey]] as a modern alternative to ''organic'', but this neologism remains relatively obscure.{{cn|date=January 2024}}

The organic compound [[isoleucine|<small>L</small>-isoleucine]] molecule presents some features typical of organic compounds: [[carbon–carbon bond]]s, [[carbon–hydrogen bond]]s, as well as covalent bonds from carbon to oxygen and to nitrogen.{{cn|date=January 2024}}

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 of [[alloys]] that contain carbon, including [[steel]] (which contains [[cementite]], {{chem2|Fe3C}}), as well as other metal and semimetal carbides (including "ionic" carbides, e.g, [[Al4C3|{{chem2|Al4C3}}]] and [[Calcium carbide|{{chem2|CaC2}}]] and "covalent" carbides, e.g. [[Boron carbide|{{chem2|B4C}}]] and [[Silicon carbide|SiC]], and graphite intercalation compounds, e.g. [[Graphite intercalation compound|{{chem2|KC8}}]]). Other compounds and materials that are considered 'inorganic' by most authorities include: metal [[carbonates]], simple [[oxides]] of carbon ([[Carbon monoxide|CO]], [[Carbon dioxide|{{chem2|CO2}}]], and arguably, [[carbon suboxide|{{chem2|C3O2}}]]), the [[allotropes]] of carbon, [[cyanides|cyanide]] derivatives not containing an organic residue (e.g., [[potassium cyanide|KCN]], [[Cyanogen|{{chem2|(CN)2}}]], [[Cyanogen bromide|BrCN]], [[cyanate]] anion {{chem2|OCN−}}, etc.), and heavier analogs thereof (e.g., [[cyaphide]] anion {{chem2|CP−}}, [[Carbon diselenide|{{chem2|CSe2}}]], [[Carbonyl sulfide|COS]]; although [[carbon disulfide]] {{chem2|CS2}} is often classed as an ''organic'' solvent). Halides of carbon without hydrogen (e.g., [[Carbon tetrafluoride|{{chem2|CF4}}]] and [[Chlorotrifluoromethane|{{chem2|CClF3}}]]), [[phosgene]] ({{chem2|COCl2}}), [[carborane]]s, [[metal carbonyl]]s (e.g., [[nickel tetracarbonyl]]), [[mellitic anhydride]] ({{chem2|C12O9}}), and other exotic [[oxocarbon]]s are also considered inorganic by some authorities.{{cn|date=January 2024}}

[[Nickel tetracarbonyl]] ({{chem2|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 and [[carbon monoxide]]. Nickel tetracarbonyl is typically classified as an ''[[organometallic compound]]'' as it satisfies the broad definition that [[organometallic 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 in [[cementite]],<ref>{{cite journal|doi = 10.1063/1.2884529|journal = [[Journal of Applied Physics]]|volume = 103|issue = 4|year = 2008|title = Structural, elastic, and electronic properties of Fe<sub>3</sub>C from first principles|first1 = C.|last1 = Jiang|first2 = S. G.|last2 = Srinivasan|first3 = A.|last3 = Caro|first4 = S. A.|last4 = Maloy|pages = 043502–043502–8|arxiv = 0711.1528|bibcode = 2008JAP...103d3502J|s2cid = 94576016}}</ref> 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.{{cn|date=February 2024}}

Metal complexes with organic ligands but no carbon-metal bonds (e.g., [[Copper(II) acetate|{{chem2|(CH3CO2)2Cu}}]]) are not considered organometallic; instead, they are called [[metal-organic compound]]s (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. Neither [[urea]] {{chem2|CO(NH2)2}} nor [[oxalic acid]] {{chem2|(COOH)2}} are organic by this definition, yet they were two key compounds in the vitalism debate. However, the [[Nomenclature of Organic Chemistry|IUPAC Blue Book]] on organic nomenclature specifically mentions urea<ref>{{cite web|url=http://www.acdlabs.com/iupac/nomenclature/79/r79_661.htm|title=IUPAC Blue Book, Urea and Its Derivatives Rule C-971|access-date=2009-11-22|archive-date=2021-05-06|archive-url=https://web.archive.org/web/20210506235155/https://www.acdlabs.com/iupac/nomenclature/79/r79_661.htm|url-status=live}}</ref> and oxalic acid<ref>{{cite web|url=http://www.acdlabs.com/iupac/nomenclature/93/r93_705.htm|title=IUPAC Blue Book, Table 28(a) Carboxylic acids and related groups. Unsubstituted parent structures|access-date=2009-11-22|archive-date=2021-06-28|archive-url=https://web.archive.org/web/20210628213602/https://www.acdlabs.com/iupac/nomenclature/93/r93_705.htm|url-status=live}}</ref> as organic compounds. Other compounds lacking C-H bonds but traditionally considered organic include [[benzenehexol]], [[mesoxalic acid]], and [[carbon tetrachloride]]. [[Mellitic acid]], which contains no C-H bonds, is considered a possible organic compound in [[Mars|Martian]] soil.<ref>{{cite journal
 |author1=S. A. Benner |author2=K. G. Devine |author3=L. N. Matveeva |author4=D. H. Powell | year = 2000
 | title = The missing organic molecules on Mars
 | journal = [[Proceedings of the National Academy of Sciences]]
 | volume = 97
 | issue = 6
 | pages = 2425–2430
 | doi = 10.1073/pnas.040539497
 | pmid = 10706606
 | pmc = 15945
 |bibcode = 2000PNAS...97.2425B |doi-access=free }}</ref> Terrestrially, it, and its anhydride, [[mellitic anhydride]], are associated with the mineral [[mellite]] ({{chem2|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, [[tetrafluoromethane|{{chem2|CF4}}]] and [[Carbon tetrachloride|{{chem2|CCl4}}]] would be considered by this rule to be "inorganic", whereas [[fluoroform|{{chem2|CHF3}}]], [[Chloroform|{{chem2|CHCl3}}]], and [[Hexachloroethane|{{chem2|C2Cl6}}]] would be organic, though these compounds share many physical and chemical properties.{{cn|date=February 2024}}