σ‐Hole bonding and hydrogen bonding: Competitive interactions

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Abstract
In certain molecular environments, a covalently‐bonded atom from Groups V–VII may have a region of significantly‐positive electrostatic potential on its outer side, along the extension of a covalent bond. This is due to the electron‐deficient outer lobe of a half‐filled p bonding orbital, which is called a “σ‐hole.” σ‐Hole bonding is the resulting highly directional noncovalent interaction that may occur with a nucleophile, e.g., a lone pair of a Lewis base. In this article, we compare the computed interaction energies and vibrational frequency shifts associated with the formation of a series of σ‐hole‐bonded and hydrogen‐bonded complexes. When the molecular environments of the atoms of Groups V–VII and the hydrogen are similar, then the hydrogen bond is usually the stronger one, although there are exceptions, as in the case of bromine. Overall, however, σ‐hole bonding can certainly be competitive with hydrogen bonding. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007