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.