Influence of screening of intramolecular easily polarizable hydrogen bonds on their infrared absorbance

Abstract

o-Xylil-diamine perchlorates (compounds 1 and 2) and o-xylil-diamine N-oxide perchlorates (compounds, 3, 4 and 5) are synthesized. It is shown by n.m.r. spectroscopy that intramolecular hydrogen bonds are formed. These bonds are structurally symmetrical and hence easily polarizable. The N⁺H⋯N ⇌ N⋯H⁺N bonds in compounds 1 and 2 are relatively long whereas the O⁺H⋯O ⇌ O⋯H⁺O bonds in compounds 3, 4 and 5 are relatively short. If these hydrogen bonds are not screened against their environment in the first type a band-like structure in the region 2800–1800 cm^–1 and a continuum extending toward smaller wavenumbers is observed, whereas with the second type a continuum is observed in the region 1800–700 cm^–1. If these hydrogen bonds are, however, screened by extended groups so that they can no longer interact strongly with their environment then instead of the continua only bands are observed. This fact confirms that the i.r. continua are caused by the various interaction effects of the easily polarizable hydrogen bonds with their environment.