Henry Rzepa's Blog

In the previous post, I explored the so-called “impossible” molecule methanetriol. It is regarded as such because the equilbrium resulting in loss of water is very facile, being exoenergic by ~14 kcal/mol in free energy. Here I explore whether changing the substituent R could result in suppressing the loss of water and stabilising the triol.

I started (as I usually do) with a search for crystal structures, in this case containing the motif shown below (trisubstituted carbon, disubstituted oxygen and  R = H or C and any type of connecting bond), which is the species resulting from loss of R^– to form a trihydroxycarbenium cation.

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What constitutes an “impossible molecule”? Well, here are two, the first being the topic of a recent article[cite]10.1021/jacs.4c02637[/cite]. The second is a favourite of organic chemistry tutors, to see if their students recognise it as an unusual (= impossible) form of a much better known molecule.

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