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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?

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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 $\ce{Al2C6(COO)6 \cdot 16H2O}$

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  • $\begingroup$ 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"? $\endgroup$ – Nilay Ghosh May 14 '20 at 9:00
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    $\begingroup$ @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. :-) $\endgroup$ – Poutnik May 14 '20 at 9:06
  • $\begingroup$ Oh I see, there are also some other minerals(Whewellite, Zhemchuzhnikovite) of organic origin but both of them possess water of crystallization :( $\endgroup$ – Nilay Ghosh May 14 '20 at 9:10
  • $\begingroup$ @Nilay Ghosh But the question is, if this hydrogen counts. $\endgroup$ – Poutnik May 14 '20 at 9:12
  • $\begingroup$ 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. $\endgroup$ – Nilay Ghosh May 14 '20 at 9:18
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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.

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