Low temperature FT-IR and molecular orbital study of N,N-dimethylglycine methyl ester: Proof for different ground conformational states in gas phase and in condensed media

Abstract

N,N-dimethylglycine methyl ester (DMG-Me) was studied by FT-IR spectroscopy under several experimental conditions, including low temperature solid state and isolated in low temperature inert gas matrices, and by molecular orbital calculations. In agreement with the theoretical predictions, the experimental data show that in the gaseous phase the most stable conformer (ASC) has the ester group in cis configuration and the N–C–CO and Lp–N–C–C (Lp = lone electron pair) dihedral angles equal to 0° and 180°, respectively, while the first conformational excited state corresponds to the doubly-degenerated-by-symmetry GSC form, where the Lp–N–C–C axis is gauche-oriented (±46.5°). On the other hand, for the matrix isolated molecule as well as in both the liquid and low temperature solid states the relative stability of the two lowest energy conformers of DMG-Me is reversed, the more polar GSC form becoming the ground conformational state. This molecule is then a remarkable example of a system showing an inversion in the order of its lowest energy conformational states due to a minor perturbation by the media such as that due to the inert gas matrix. Full assignment of the spectra obtained in the different experimental conditions used is also presented.