Molecular structure and vibrational spectra of methyl glycolate and methyl α-hydroxy isobutyrate

Abstract

Conformational isomerism in isolated and liquid methyl glycolate and methyl α-hydroxy isobutyrate was investigated by a concerted molecular orbital and vibrational spectroscopic approach (infrared and Raman). The molecular structures, relative energies, dipole moments and vibrational spectra of the various possible conformers of the studied compound were calculated, using the extended 6-31G* basis set at the HF-SCF ab initio level of theory. The theoretical results were then used to interpret infrared and Raman data obtained under different experimental conditions. It was found that both in the liquid and gaseous phase the studied molecules exist in two experimentally observed conformational states, the Cs point group Syn–syn conformer (Ss), which exhibits an intramolecular OH⋯O hydrogen bond, being the most stable form. As expected, the relative populations of the second more stable conformers increase in the liquid phase, since intermolecular interactions tend to reduce the importance of the intramolecular H-bonding that is the main stabilizing factor of the Ss forms.