Raman and IR spectral measurements in the 3500 – 400 cm-1 have been carried out for the solid sample of (R)-(+)-α-Methylvaline. The spectral features indicated that the molecule is a zwitterion, as is true of amino acids, and is involved in H-bonding, namely, intermolecular –N-H···O bonding. To account for these aspects, we have determined a zwitterionic stable monomer structure in water as a solvent at B3LYP/6- 311++G(d,p) level, and from this monomer, a dimer species with –N-H···O bonding is constructed. On the basis of NBO analysis, it has been shown that the delocalization of electron densities between lone pair (LP) of Oxygen with the anti-bonding (σ* ) orbital of N-H moiety is consistent with the geometrical structure of the dimer. Molecular electrostatic potentials have been used to demonstrate intermolecular donor (O) – acceptor (-NH) interaction. Predicted deformation modes for –NH3 + and CO2¯ are in fair agreement with measured frequencies than stretching modes.

Keywords : (R)-(+)-α-Methylvaline; IR; Raman; DFT; NH···O Bonding