Structure and vibrational spectra of -hydroxy isobutyric acid in the crystalline and glassy phases and isolated in inert gas matrixes

Abstract

Infrared spectra of monomeric -hydroxy isobutyric acid (HIBA) isolated in argon, krypton and xenon matrixes (at 8 K) are reported. It is shown that in all the studied matrixes HIBA exists preferentially as the intramolecularly H-bonded SsC conformer, where the HOCC, OCCO and OCOH dihedrals are 0°. In addition to the SsC form, two higher energy conformers (AaT and GskC) could be observed experimentally for the first time. The spectra of the three observed conformers were assigned on the basis of density functional theory calculations (B3LYP/6-31G*) and their relative energies estimated from relative band intensities. Raman and infrared spectra of both crystalline and low temperature glassy states were also recorded and interpreted. In consonance with previously reported X-ray structural studies (W. P. J. Gaykema, J. A. Kanters and G. Roelofsen, Cryst. Struct. Commun., 1978, 7, 463), the vibrational data now obtained are consistent with the exclusive presence in the crystalline phase of molecules assuming a conformation similar to that of the lowest energy monomer observed in the matrixes (SsC conformer).