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While studying the main groups of p-block, I have seen many compounds being labeled as an analog to some popular organic compound. For example, borazine is termed as 'inorganic benzene', while boron nitride has been called 'inorganic graphite'.

Now, my question is, whether these monikers (if that's what they may be called?) reflect just the structural likeness, the chemical similarities or, perhaps, both?

Moreover, are there some other examples which illustrate this?

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    $\begingroup$ It is because of the structural likeness, but I wouldn't use the analogies. $\endgroup$
    – MaxW
    Jan 15, 2021 at 10:10
  • $\begingroup$ @MaxW won't the structural similarities, in some slight manner, cause similarity in certain chemical characteristics? Say, for example, why couldn't borazine show EAS ? I am not saying that it does, and in general I have no clue about its chemical properties, but can't I imagine the substitution of a proton by an equivalently monovalent ion, say, a halogen? $\endgroup$
    – user95829
    Jan 15, 2021 at 10:23
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    $\begingroup$ I just think making such analogies is ripe for creating misunderstandings. For example in benzene all the hydrogen are equivalent. That obviously isn't true in borazine. $\endgroup$
    – MaxW
    Jan 15, 2021 at 10:31
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    $\begingroup$ Yes, I agree. But, then again, many sources cite them as such, so these analogies are quite the trend, rather than some one-off author trying infuse fun into a fact. $\endgroup$
    – user95829
    Jan 15, 2021 at 10:39

2 Answers 2

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I would not call graphite organic, but there is no clear-cut way of defining organic and inorganic compounds.

To your question, the pairs of compounds are isoelectronic. That means that if we assume that molecular orbitals (MOs) arise from atomic orbitals, the corresponding MOs in the two compounds have the same occupancy. In these cases it arises because the number of electrons in the dimer BN is the same as in the dimer CC. Another example of isoelectronic compounds would be N$_2$ and CO. Being isoelectronic, they do share some properties, e.g. both N$_2$ and CO have a triple bond. If only the valence electrons are identically occupied, we call them isovalent, which would include e.g. H$_2$O and H$_2$S.

The bonding of benzene and borazine differs in that not all sites are equivalent, but the form of the MOs is broadly similar and the same applies to boron nitride. Similarity in MOs is then reflected in similarity in reactivity. (Even though they are not that similar in reactivity.)

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    $\begingroup$ If one takes the 1 graphite plane structure formally as extrapolation of e.g. coronene toward the infinite 2D size...... $\endgroup$
    – Poutnik
    Jan 25, 2021 at 6:20
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My take is that the terms "inorganic benzene" and "inorganic graphite" are meant to relay thoughts of both structural and chemical likeness to organic counterparts; however, graphite is not an organic compound since it is not a compound. It is an allotrope of carbon, just like diamond, buckminsterfullerene and graphene.

The IUPAC standards establish a common language for chemical researchers and hence what is an organic compound and what is an inorganic compound.

Probably the best examples of comparisons of organic and inorganic compounds, their similarities and differences, would be the work to evaluate whether sulfur-, boron-, and silicon-based life is possible. (The most plausible is probably silicon.) See Petkowski et. al. for a recent paper that includes an overview of the basic physico-chemical properties of carbon and silicon, including their respective bond and common functional group reactivity.

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