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[1]. 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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References

1. J.H. Marks, X. Bai, A.A. Nikolayev, Q. Gong, C. Zhu, N.F. Kleimeier, A.M. Turner, S.K. Singh, J. Wang, J. Yang, Y. Pan, T. Yang, A.M. Mebel, and R.I. Kaiser, "Methanetriol─Formation of an Impossible Molecule", Journal of the American Chemical Society, vol. 146, pp. 12174-12184, 2024. https://doi.org/10.1021/jacs.4c02637