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Organic compounds are typically defined as compounds containing carbon and nearly all contain hydrogen as well. Which organic compounds do not contain hydrogen?

suse
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    e. g. $$\ce{ CCl4}$$ – Karsten May 14 '20 at 03:33
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    @Karsten Theis: And $\ce{CBr4}$. How about diamond and graphite? :-) – Mathew Mahindaratne May 14 '20 at 03:45
  • $\ce{ CS2}$, $\ce{ CO2}$, $\ce{ CO3^2-}$, $\ce{(CN)2}$, – imalipusram May 14 '20 at 04:16
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    @KarstenTheis https://chemistry.stackexchange.com/questions/49704/should-carbon-tetrachloride-really-be-considered-an-organic-compound – Nilay Ghosh May 14 '20 at 04:37
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    @imalipusram https://chemistry.stackexchange.com/questions/22195/is-carbon-dioxide-organic-or-inorganic – Nilay Ghosh May 14 '20 at 04:43
  • what about $C_{60}$ and other fullerenes? – porphyrin May 14 '20 at 08:18
  • @porphyrin I guess there is a thin ice here. Are graphite and diamond organic polymers ? Sometimes, distinguishing organic and inorganic substances is very formal. As we say CX4 are organic compounds, we should also say carbon does not form carbon halogenides, which are inorganic compounds. – Poutnik May 14 '20 at 08:32
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    I agree that the distinction organic/inorganic is somewhat arbitrary and is rather pointless anyway. The compartmentalisation of chemistry has had the unfortunate effect of holding the subject back. – porphyrin May 14 '20 at 08:45
  • Does organometallic compounds count? eg. Ni(CO)4? – Nilay Ghosh May 14 '20 at 09:03
  • I’m voting to close this question because it is too broad. – Mathew Mahindaratne May 14 '20 at 10:07
  • Another definition I've seen of organic is that it contains BOTH hydrogen AND carbon. In that case not containing H would render a compound inorganic. But as others point out, the usefulness of such definitions is largely arbitrary and of questionable utility. – Buck Thorn May 16 '20 at 07:46

2 Answers2

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Distinguishing organic and inorganic substances is often very formal. We say CX4 are organic compounds, we should also say carbon does not form carbon halogenides, which are inorganic compounds.

One of more known halogen-hydrogen-free examples is carbon suboxide $\ce{C3O2}$, $\ce{O=C=C=C=O}$, that is somehere on inorganic-organic border, being often considered as the second anhydride of malonic acide $\ce{HOOC-CH2-COOH}$, as it is prepared from it by $\ce{P4O10}$ aggressive dehydratation.

But the true malonic anhydride has 4-atom cycle.

One of less known examples is the anhydride of the mellitic acid, which could be formally considered as a carbon oxide with the summary formula $\ce{C12O9}$

... [mellitic anhydride] is one of the only four [oxides] that are reasonably stable under standard conditions. It is a white sublimable solid, apparently obtained by Justus Liebig and Friedrich Wöhler in 1830 in their study of Mellite

As an interesting side info:

Mellite, also called honeystone, is an unusual mineral being also an organic chemical. Chemically identified as an aluminium salt of mellitic acid; that is, aluminium benzene hexacarboxylate hydrate, with the chemical formula $\ce{Al2C6(COO)6 \cdot 16H2O}$

Poutnik
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  • Mellite possess water of crystallization. So, it can be considered to have hydrogen atoms. Doesn't it disqualify it from the set of "organic compounds not having hydrogen"? – Nilay Ghosh May 14 '20 at 09:00
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    @Nilay Ghosh You have misinterpreted my answer, probably due my wrong answer layout. Mellite mentioning was intended as an interesting side information related to the anhydride, not as an another example. :-) – Poutnik May 14 '20 at 09:06
  • Oh I see, there are also some other minerals(Whewellite, Zhemchuzhnikovite) of organic origin but both of them possess water of crystallization :( – Nilay Ghosh May 14 '20 at 09:10
  • @Nilay Ghosh But the question is, if this hydrogen counts. – Poutnik May 14 '20 at 09:12
  • Yes, OP's question sounds vague to me. Is OP asking for organic compounds not having hydrogen atoms or organic compounds not having hydrogen bond (C-H bond)? If OP is asking for the 1st question, then CX4 (X=halogen) counts and if OP is asking for 2nd question, then oxalic acid and benzenehexol counts. – Nilay Ghosh May 14 '20 at 09:18
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It depends, of course, on what "organic" means. If we define "organic compounds" as "carbon compounds generated by biological processes", then carbon dioxide is an obvious choice. But, of course, most chemists consider that an inorganic compound. A choice more likely to be favored by chemists is carbon disulfide, which Wikipedia reports is produced in trace quantities from marshes.

Oscar Lanzi
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