On the hydrogen bonding abilities of phenols and anisoles

The difference in the hydrogen bond acceptor strengths of phenol and anisole in their planar and perpendicular conformation has been studied to assess the effect of conjugation with a π system on the acceptor strength of an oxygen atom. Intermolecular perturbation theory calculations were used, together with an analysis of hydrogen bond formation in molecular crystal structures. Anisoles and phenols form hydrogen bonds which are intermediate in strength between those of furan and tetrahydrofuran, and are a few kJ/mol stronger for the perpendicular conformations than the planar conformations. This can be partly attributed to the change in the oxygen charge distribution with conformation.