Henry Rzepa's Blog Chemistry with a twist

March 25, 2017

First, hexacoordinate carbon – now pentacoordinate nitrogen?

A few years back I followed a train of thought here which ended with hexacoordinate carbon, then a hypothesis rather than a demonstrated reality. That reality was recently confirmed via a crystal structure, DOI:10.5517/CCDC.CSD.CC1M71QM[1]. Here is a similar proposal for penta-coordinate nitrogen.



  1. M. Malischewski, and K. Seppelt, "Crystal Structure Determination of the Pentagonal-Pyramidal Hexamethylbenzene Dication C6 (CH3 )6 2+", Angewandte Chemie International Edition, vol. 56, pp. 368-370, 2016. http://dx.doi.org/10.1002/anie.201608795

September 21, 2012

The ten-electron homologue of semibullvalene.

Filed under: Interesting chemistry — Tags: , , , — Henry Rzepa @ 10:00 am

Semibullvalene is a molecule which undergoes a facile [3,3] sigmatropic shift. So facile that it appears this equilibrium can be frozen out at the transition state if suitable substituents are used. This is a six-electron process, which leads to one of those homologous questions; what happens with ten electrons?


April 16, 2010

Carbobenzene: benzene with a difference

Filed under: General — Tags: , , , , — Henry Rzepa @ 10:44 am

Some molecules, when you first see them, just intrigue. So it was with carbobenzene, the synthesis of a derivative of which was recently achieved by Remi Chauvin and co-workers (DOI: 10.1002/chem.200601193). Two additional carbon atoms have been inserted into each of the six C-C bonds in benzene.


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