Hydrogen bonding and internal rotation barriers of glycine and its zwitterions (hypothetical) in the gas phase

Abstract

The structures of the major glycine conformers, and several transition state structures, were optimized at HF/6-31G* and HF/6-31 + G* levels of theory and the correlation energies were calculated at MP2/6-31G* and MP2/6-31 + G** levels on these geometries, respectively. The heat of formation of gas phase glycine is calculated to be[Formula: see text]. Thermodynamic properties, [Formula: see text] etc. are calculated as functions of temperature using standard statistical thermodynamic methods. MP2/6-31 + G* optimization was carried out on the zwitterion, found by HF/6-31 + G* optimization to be a local minimum. The results suggest that glycine in the zwitterionic form in the gas phase is not a stationary point. Zwitterionic glycine does not exist in the gas phase.