Methyl Groups as Hydrogen Bond Acceptors via Their sp3 Carbon Atoms

Abstract

We report herein a combined structural and theoretical study of a novel hydrogen bond in which a methyl group, when bound to an electropositive atom E, acts as the acceptor via its carbon atom. A significant number of experimental examples of such interactions have been retrieved from the Cambridge Structural Database, showing a clear trend toward a linear arrangement of the two interacting groups (E–CH3···H–Y) as the interatomic distance shortens. The hydrogen bond has been further investigated by means of different computational techniques in order to assess its strength and nature. We have also unveiled, by means of natural bond orbital analysis, a charge transfer from a σ(E–C) bonding orbital of the methyl group to a σ* antibonding H–Y orbital.