Simultaneous α-Hole and Hydrogen Bonding by Sulfur- and Selenium-Containing Heterocycles

when a Group V, VI, or VII atom forms a covalent bond, its bonding orbital has a deficiency of electronic charge in its outer (noninvolved) lobe. This is called a alpha-hole. If the atom is sufficiently polarizable, the (T-hole may have a positive electrostatic potential which can interact with a nucleophilic site in its proximity to form a noncovalent bond. In this article, we show computationally, for a series of sulfur and selenium heterocycles, how the two alpha-holes on each S or Se atom are affected by changes in the molecular framework and substituents. It is possible to selectively design alpha-holes of appropriate strength and orientation for Specific purposes, e.g. drug-receptor interactions or crystal engineering. (C) 2008 Wiley Periodicals, Inc. Int J Quantum Chem 108: 2770-2781, 2008