A SIMPLE RELATIONSHIP BETWEEN INFRA-RED STRETCHING FREQUENCIES AND HYDROGEN BOND DISTANCES IN CRYSTALS

A new empirical relationship between the X-H⋯Y distance R and the stretching frequency Δvs of the X-H bond is presented. In the preceding paper it is suggested that repulsive forces in hydrogen bonds are due principally to Van der Waals repulsions between the non bonding orbitala of the X and Y atoms. The present correlation is based on the calculation of these Van der Waals forces by means of a Lennard-Jones (6-12) potential function. The equation is given by {A figure is presented} where the values of d approximate to the sum of the collision radii of the X and Y atoms, and are 3·2, 3·35, 3·4, 3·4, 3·6, 3·85 and 3·9 for the F-H⋯F, O-H⋯O, N-H⋯F, N-H⋯O, N-H⋯N, O-H⋯Cl and N-H⋯Cl hydrogen bonds respectively. © 1969.