Hydrogen-bond directionality at the donor H atom—analysis of interaction energies and database statistics

Abstract

A thorough analysis has been performed on the effects of varying the angle at the donor hydrogen in hydrogen bonds using database studies and ab initio intermolecular interaction energy calculations. Non-activated C–Hacceptor interactions are seen to have a weak energy dependence on the D–HA angle, but for all of the conventional hydrogen-bonds studied the D–HA angle has a range of 40–65° within an energy penalty of RT (2.5 kJ mol⁻¹). Interactions with D–HA angle in the range 120–140° are seen to have substantially reduced stabilisation energies and angles below 120° are generally unlikely to correspond to significant interactions.