The sign in the energy in the bond critical point

I want to share this bit of  knowledge with you, random internet people. It is related with the use, and abuse, that is given to the concept of “bond path” by some of the proponents of the Quantum Theory of Atoms in Molecules[1] (QTAIM). I found it in a paper by Cremer et al[2] (here they use the term MED, Maximum Electron Density path to refer to the Bond Path of QTAIM):

“…the existence of a MED path is only a necessary condition for covalent bonding,which has to be complemented by the sufficient condition that the energy density at the path-critical point rc,i.e., Hc = H(rc)= Vc + Gc is negative, thus indicating stabilizing attractive interactions between the atoms connected by the MED path. A negative Hc value is caused by a negative (stabilizing) potential energy density outweighing the positive (destabilizing) kinetic energy density[3,4].

I think is important to make this distinction. A bond path, even though it act as a privileged exchange channel[5], should not be the final criteria to determine. not the existence of a bond, nor the nature of the interaction between atoms.

So, that’s it, goodbye, and good luck.

[1] Bader, Richard. Atoms in Molecules: A Quantum Theory. USA: Oxford University Press, 1994. ISBN 978-0-19-855865-1.
[2] Kalescky, R., Kraka, E., & Cremer, D. Description of aromaticity with the help of vibrational spectroscopy: anthracene and phenanthrene. J. Phys. Chem. A 2014, 118(1), 223–37. doi:10.1021/jp4092514
[3] Cremer, D.; E., K. A Description of the Chemical Bond in Terms of Local Properties of Electron Density and Energy, in Conceptual Approaches in Quantum Chemistry − Models and Applications. Croatica Chem. Acta 1984, 57, 1259−1281
[4] Cremer, D.; E., K. Chemical Bonds without Bonding Electron Density – Does the Difference Electron Density Analysis Suffice for a Description of the Chemical Bond? Angew. Chem., Int. Ed. Engl. 1984, 23, 627−628.
[5] Pendás, A. M., Francisco, E., Blanco, M. A., & Gatti, C. Bond paths as privileged exchange channels. Chemistry (Weinheim an Der Bergstrasse, Germany) 2007 13(33), 9362–71. doi:10.1002/chem.200700408


Acerca de José Manuel

I'm from Mexico and currently in a PhD program in the University of Oviedo, in Spain.
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