Archive for October, 2019

Does Kekulene have Kekulé vibrational modes? Yes!

Saturday, October 19th, 2019

Increasingly, individual small molecules are having their structures imaged using STM, including cyclo[18]carbon that I recently discussed. The latest one receiving such treatment is Kekulene.[1]



  1. I. Pozo, Z. Majzik, N. Pavliček, M. Melle-Franco, E. Guitián, D. Peña, L. Gross, and D. Pérez, "Revisiting Kekulene: Synthesis and Single-Molecule Imaging", Journal of the American Chemical Society, vol. 141, pp. 15488-15493, 2019.

Catalytic Mitsunobu reaction.

Wednesday, October 9th, 2019

If, as a synthetic chemist, you want to invert the configuration of an alcohol in which the OH group is at a chiral centre, then the Mitsunobu reaction has been a stalwart for many years. Now a catalytic version has been published, [1] along with a proposed mechanism. Here I apply computation as a reality check to see what the energetics of this mechanism might be.



  1. R.H. Beddoe, K.G. Andrews, V. Magné, J.D. Cuthbertson, J. Saska, A.L. Shannon-Little, S.E. Shanahan, H.F. Sneddon, and R.M. Denton, "Redox-neutral organocatalytic Mitsunobu reactions", Science, vol. 365, pp. 910-914, 2019.

Bond length alternation (BLA) in large conjugated rings: an (anti-aromatic) update.

Thursday, October 3rd, 2019

In the previous post, I looked at a class of molecule known as hexaphyrins, inspecting bond length alternation (BLA) at the so-called meso position, the carbon atom joining two pyrrole rings. A search of the difference in bond lengths at this position had shown two significant clusters of crystal structures.
Molecules in the bottom left of this diagram shows little or no bond length alternation. The right middle shows another cluster with more extreme (and unequal) bond length alternation. I have selected one molecule from this cluster, EGIJEK and it differs from EGIHUY in having four NH units in the ring, whereas the latter has only two.