Hydrogen Bonding: A Coulombic σ‑Hole Interaction

Abstract

Molecular electrostatic potentials, in conjunction with polarization,
provide the key to understanding hydrogen bonding. As required
by the Hellmann–Feynman theorem, hydrogen bonding is a Coulombic
interaction between (a) a positive electrostatic potential associated with
a region of lower electronic density on the hydrogen (a σ-hole), and (b)
a negative site on the hydrogen-bond acceptor. The charge distributions
of both the hydrogen-bond donor and the acceptor reflect the polarizing
effects of each other’s electric fields. The greater the polarization, the
stronger the interaction. This interpretation of hydrogen bonding applies
to all of the different categories into which it has been subdivided; they
are fundamentally similar. We show that if polarization is minor and the
hydrogen bonds relatively weak, then their interaction energies correlate
well with the product of the most positive electrostatic potential on the
hydrogen and the most negative one on the negative site. It is argued
that the partial covalent character that is often attributed to hydrogen
bonds simply reflects a greater degree of polarization.