Vibrational spectra and conformational isomerism of calixarene building blocks: 2-benzylphenol

Abstract

The conformations and vibrational spectra of 2-benzylphenol have been analysed within the framework of scaled quantum mechanics. It is shown that the solid-state conformation of the 2-benzylphenol molecule corresponds to one of four potential energy minima predicted by non-empirical quantum chemical calculations for the isolated molecule. In the molten state and in diluted CCl₄ solutions of the title compound this conformer coexists with another two spectroscopically detected conformations. The presence of several conformers gives rise to the observation of the corresponding number of ν_sCH₂ and ν_asCH₂ bands in the IR spectra, thus providing experimental evidence of the conformational sensitivity of the νCH₂ frequencies. It is shown that νCH₂ wavenumbers of different kinds of molecules, containing diphenylmethane fragments, are determined by the dihedral angles between the planes of the aromatic rings and the plane of the connecting methylene bridges, except for the case of short intramolecular contacts with the participation of the methylene protons.