Polarization IR spectra of the hydrogen bond in 2-oxazolidone crystals: isotopic dilution effects in the crystalline spectra

Abstract

This paper has been devoted to investigation of polarized IR spectra for hydrogen bonded 2-oxazolidone crystals. The crystalline spectra were measured in the frequency range of the proton and the deuteron stretching vibrations, ν N–H and ν N–D, at room temperature and at temperature of the liquid nitrogen, for perpendicular orientation of the incident IR beam, with respect to the “ bc” crystal face. Investigation of “ residual” ν N–H bands, measured for partially deuterated crystalline samples of 2-oxazolidone, revealed some substantial changes in shapes and in dichroic properties of these bands, accompanying to the deuterium substitution rate approaching 100%. These effects prove of a random distribution of protons and deuterons in the infinite, open chains of hydrogen bonds, forming the crystal lattice. Such distribution of hydrogen isotope atoms is responsible for annihilation of vibrational Davydow couplings in the crystal hydrogen bond system. This effect remains in a good agreement with prediction derived from a general vibronic model of H/D isotopic “ self-organization” processes in hydrogen bond dimers. A fully random distribution of hydrogen isotope atoms in adjacent hydrogen bonds in the hydrogen bond chains become possible, due to relatively weak coupling of electronic motions in the associated molecules, with the proton stretching vibrations in the hydrogen bonds.