SIGNIFICANCE OF INFRA-RED FREQUENCY SHIFTS IN RELATION TO HYDROGEN BOND STRENGTHS

The origin of the various lines relating Δv (XH) with X....Y distances in hydrogen bonds is discussed. The plots are consistent with the hypothesis that the terminal atoms approach to a distance comparable with their Van der Waals' radii and that any further contraction is only possible if hydrogen bonds are formed. This implies that in bonding situations the effective radius of the hydrogen atom itself is small and can be ignored. This hypothesis has a number of experimental implications. Significant deviations from plots of the Bellamy/Hallam/Williams type are to be expected in certain circumstances. These have been sought for and found. Anomalies are also to be expected in the results of basic strength measurements using Δv values. These also have been observed. The special cases of {A figure is presented} dimers and of intramolecular hydrogen bonds are discussed and it is shown that some order can be introduced on the basis of this hypothesis. © 1969.