Calculations on vibrational properties of H-bonded OH groups, as a function of H-bond geometry

Abstract

Ab initio calculations on (H 2O) 2 have been performed on 10 model geometries and 17 geometries which simulate OH⋯O contacts encountered in the crystals of β- d-fructose, β- d-arabinose and turanose. The variations with geometry of the hydrogen-bond energy Δ E, the lengthening of the donor OH distance (Δ r), the frequency shift Δν OH and the IR absorption intensity I are investigated. The relation between Δν OH and Δ r is discussed and it is found that most of the observed Δν OH arises from Δ r. It is shown that there is no one-to-one correspondence between Δν OH, Δ E and I. In particular, Δ E may be large even for cases where Δν OH is small. The results are used to determine which OH⋯O contacts give rise to the narrow OH bands observed in the saccharide crystals.