Matrix-isolation FT-IR spectra and molecular orbital calculations on neutral N,N-dimethylglycine

Abstract

The structures and vibrational spectra of the preferred conformers of the neutral form of N,N-dimethylglycine (DMG) were studied by a combined approach, using DFT(B3LYP)/6-311++G** and MP2/6-31++G** calculations and low temperature matrix isolation IR spectroscopy. The conformational ground state was found to be the intramolecularly O–HN hydrogen-bonded GAT form, where the (lone pair)-N–C–C and N–C–CO dihedral angles are 30° (gauche; G) and ca. 180° (anti; A), respectively, and the carboxylic group assumes the trans (T) configuration (OC–O–H dihedral angle equal to 180°). The presence in the matrices of two additional conformers, where the carboxylic moiety assumes the most commonly found cis (C) conformation and the N–C–CO axis adopts the syn arrangement (the two conformers differ only in the positions of the methyl groups), could also be established. Observation of these conformers is in consonance with the theoretical predictions, which indicate that the observed conformers should differ in energy by less than 7 kJ mol−1. Full assignment of the observed infrared spectra of both DMG and its -OD isotopomer in Ar and Xe matrices was carried out on the basis of comparison with the theoretically predicted spectra and temperature variation experiments.