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In chemistry, organic chemical compounds are classified as compounds that have a C-H bond or C-C bond, or both. However, this definition is not absolute, and many other organizations or groups have different classifications. IUPAC does not offer a definition of "inorganic" or "inorganic compound" but does define inorganic polymer as "...skeletal structure that does not include carbon atoms."<ref>https://goldbook.iupac.org/html/I/IT07515.html</ref> The Inorganic Crystal Structure Database (ICSD) defines as "inorganic" carbon compounds, compounds that may contain either C-H or C-C bonds, but not both.<ref>https://web.archive.org/web/20170830061100/https://icsd.fiz-karlsruhe.de/search/resources/content/sci_man_ICSD_v1.pdf</ref>

For historical reasons discussed below, a few types of carbon-containing compounds, such as carbides, carbonates, simple oxides of carbon (for example, CO and CO<sub>2</sub>), and cyanides are considered inorganic. Allotropes of [[carbon]], such as diamond, graphite, fullerenes, and carbon nanotubes are also excluded because they are simple substances composed of only a single element and therefore allotropes are not generally considered to be true chemical compounds. 

==Specific cases==
===[[Guanidine]]===
Like [[urea]], guanidine lacks C-H or C-C bonds and only has C-NH bonds, but it's often classified as organic.

===[[Hydrogen cyanide]]===
The exact classification of HCN as organic or inorganic remains unresolved. Going by the C-H bond definition, HCN would be organic, but in aqueous solution it dissociates into H<sup>+</sup> and CN<sup>-</sup>, and since the cyanide ion is a [[pseudohalogen]], this makes it inorganic.

===[[Metal carbonyl]]s===
Although [[carbon monoxide]] is universally classified as inorganic, metal carbonyls are often classified as organometallic compounds and are always referenced and researched in organic chemistry, but not in inorganic chemistry.

===Mellitic acid===
Like oxalic acid, this compound lacks C-H bonds, but it has an aromatic (benzene) ring made of C-C bonds, which holds 6 carboxyl groups.

===Mellitic anhydride===
Mellitic anhydride lacks any C-H bonds, but it has a benzene ring and 3 organic carboxylic anhydride bound to the aromatic ring. Hydrolysis of this compound gives mellitic acid, which is an organic compound, which, like [[oxalic acid]], lacks any C-H bonds. Since this compound is often classified as oxocarbon or carbon oxide, mellitic anhydride is considered inorganic by most definitions.

===[[Oxalic acid]]===
Oxalic acid lacks C-H bonds, but it does have a C-C bond.

===Perhalocarbons===
Perhalocarbon compounds are hydrocarbons where the hydrogen atoms have been replaced by halogen atoms. Examples include [[carbon tetrachloride]], perfluorocarbons, etc. Perhalocarbons have very different properties from their hydrocarbon parent.

Perhalocarboxylic acids, like [[trifluoroacetic acid]] are sometimes classified as inorganic, though more often they're classified as organic.

===[[Urea]]===
Urea lacks any C-H or C-C bonds, however, it does have C-NH<sub>2</sub> bonds, which are omnipresent in many organic compounds.

==References==
<references/>
===Relevant Sciecnemadness threads===

*[http://www.sciencemadness.org/talk/viewthread.php?tid=63022 Is HCN organic or inorganic?]

[[Category:Chemical compounds]]