HYDROGEN BONDING IN 2-METHYL- AND 2-DIMETHYLAMINOETHANOL BY MICROWAVE SPECTROSCOPY

Abstract

From their microwave spectra, $2-methylaminoethanol^{1}$ and 2-dimethylaminoethanol have been found to have gauche OCCN configurations and $O-H\cdots N$ type intramolecular hydrogen bonds. The conformational equilibrium between two rotamers of the former, one with a trans CCMC configuration (``GT”) and one with a gauche CCNC configuration (“GG”) favors the “GT” form, due to a ground state $\Delta$E of 0.46 kcal/mole. The configurations about the central C-N bonds. compared to that of $2-aminoethanol,^{2}$ reflect the combined influence of the hydrogen bond, the $C-N$ internal rotation barrier and a 1,4 nonbonded hydrogen repulsion. The differences between the observed and predicted dipole components suggest a 0.5 D polarization of the nitrogen nonbonding electrons by the hydroxy proton. The hydroxy $d_{1}$ spectrum of 2-dimethylaminoethanol is consistent with either an extraordinarily Long O-H bond (1.235\AA) or an approximate 0.01\AA shrinkage in the $O\cdots N$ distance accompanying deuteration.