Henry Rzepa's Blog Chemistry with a twist

April 13, 2018

A record polarity for a neutral compound?

In several posts a year or so ago I considered various suggestions for the most polar neutral molecules, as measured by the dipole moment. A record had been claimed[1] for a synthesized molecule of ~14.1±0.7D. I pushed this to a calculated 21.7D for an admittedly hypothetical and unsynthesized molecule. Here I propose a new family of compounds which have the potential to extend the dipole moment for a formally neutral molecule up still further.



  1. J. Wudarczyk, G. Papamokos, V. Margaritis, D. Schollmeyer, F. Hinkel, M. Baumgarten, G. Floudas, and K. Müllen, "Hexasubstituted Benzenes with Ultrastrong Dipole Moments", Angewandte Chemie International Edition, vol. 55, pp. 3220-3223, 2016. http://dx.doi.org/10.1002/anie.201508249

December 24, 2016

The dipole moments of highly polar molecules: glycine zwitterion.

The previous posts produced discussion about the dipole moments of highly polar molecules. Here to produce some reference points for further discussion I look at the dipole moment of glycine, the classic zwitterion (an internal ion-pair).


February 7, 2016

A molecular balance for dispersion energy?

The geometry of cyclo-octatetraenes differs fundamentally from the lower homologue benzene in exhibiting slow (nuclear) valence bond isomerism rather than rapid (electronic) bond-equalising resonance. In 1992 Anderson and Kirsch[1] exploited this property to describe a simple molecular balance for estimating how two alkyl substituents on the ring might interact via the (currently very topical) mechanism of dispersion (induced-dipole-induced-dipole) attractions. These electron correlation effects are exceptionally difficult to model using formal quantum mechanics and are nowadays normally replaced by more empirical functions such as Grimme's D3BJ correction.[2] Here I explore aspects of how the small molecule below might be used to investigate the accuracy of such estimates of dispersion energies.



  1. J.E. Anderson, and P.A. Kirsch, "Structural equilibria determined by attractive steric interactions. 1,6-Dialkylcyclooctatetraenes and their bond-shift and ring inversion investigated by dynamic NMR spectroscopy and molecular mechanics calculations", Journal of the Chemical Society, Perkin Transactions 2, pp. 1951, 1992. http://dx.doi.org/10.1039/P29920001951
  2. S. Grimme, S. Ehrlich, and L. Goerigk, "Effect of the damping function in dispersion corrected density functional theory", Journal of Computational Chemistry, vol. 32, pp. 1456-1465, 2011. http://dx.doi.org/10.1002/jcc.21759

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