The Role of the Lone Pairs in Hydrogen Bonding

Abstract

The paper discusses some aspects of the electron lone-pairs in H-bonded structures: their role in determining the short-range structure and the effect of the environment on the electron density. In the water molecule the entire non-bonded region appears to be equally accessible for hydrogen bonding and the details of the hydrogen-bond arrangement are mainly determined by simple geometrical and topological requirements. Many examples may be taken to illustrate that it is important to take the whole electron and nuclear distribution into account when discussing the relative arrangement of interacting molecules. The resulting structure of one particular compound is determined by the net balance of many intermolecular interactions and not only by the hydrogen bonding, even if the resulting structure is consistent with hydrogen-bond directionality. From structural data it can be concluded that the immediate acceptor of a hydrogen bond is some negative charge accumulation, such as in a lone-pair region, but not specifically any individual lone pairs in the traditional, atomic sense.