Spectroscopic detection of an intramolecular hydrogen bond in 2-hydroxybenzophenone derivatives

Abstract

The present paper is devoted to an analysis of the infrared spectra of 2-hydroxybenzophenone derivatives in order to determine the influence of intramolecular interactions on the positions and shapes of the vibrational bands of the various atomic groups in the solid, liquid (solution) and vapor states. There is scattered information in the literature only on the positions of individual absorption bands [2-4]. We have made a systematic investigation of the IR spectra of 11 derivativesof 2-hydroxybenzophenone over a wide spectral range. The possible assignment of the vibrational frequencies has been given. The selection of substances for investigation was governed by the fact that we subsequently used the 2-hydroxybenzophenone derivatives to investigate the nature of the intermolecular interactions in solutions. To prepare solid samples, the substances were molded with KBr in vacuum under a pressure of seven tonnes/cm 2. The IR spectra were recorded on a UR-20 double-beam spectrophotomete r in the range from 3700 to 400 cm -1 (program 4). The spectra of solutions were obtained by means of dismountabte cells with KBr windows. The spectral slit width in the region of absorption of carbonyl groups was ~8 cm -I and in that of hydroxy groups ~4 cm -t. The spectra of the vapors were recorded* on a Perkin--Elmer 325 double-beam speetrophotomete r using heated ceils 7.8 cm long with NaC1 windows. The spectral slit width in the 1600 cm -1 region was 0.5-1 cm -1. The following structural formula and numbering were adopted for benzophenone: