Methyl Groups as Hydrogen Bond Acceptors via Their sp3 Carbon Atoms

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 center dot center dot center dot 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 sigma(E-C) bonding orbital of the methyl group to a sigma* antibonding H-Y orbital.

Automated summary

The study explores a novel hydrogen bond where a methyl group, bound to an electropositive atom, acts as the acceptor through its carbon atom. Experimental examples from the Cambridge Structural Database show a trend towards a linear arrangement of interacting groups as the interatomic distance decreases. Computational techniques were used to investigate the strength and nature of the hydrogen bond, revealing charge transfer from a sigma(E-C) bonding orbital of the methyl group to a sigma* antibonding H-Y orbital.