Internal hydrogen bond, torsional motion, and molecular properties of 2-methoxyethylamine by microwave spectroscopy: Methyl barrier to internal rotation for 2-methoxyethanol

Abstract

The microwave spectra of four substituted isotopic species of 2-methoxyethylamine (NH 2, NHD, NDH, ND 2) have been assigned. The molecule is found to exist in a gauche form with an intramolecular hydrogen bond of the NH⋯O type. The four possible sets of the amino hydrogen r s corrdinates give different H⋯H distances, probably because the -NH 2 group is involved in large amplitude vibrations and because of changes in the heavy atom positions arising from the deuteration of the hydrogen bond. For the most abundant species many vibrational states have been analyzed and assigned to the two possible CO torsions in the molecule. A value V 3 = 3150 ± 50 cal/mol was found for the methyl torsional barrier and V 1 = 9 ± 3 kcal/mol for the other CO torsional barrier. A third set of observed vibrational satellites is probably assignable to the CC torsion. The determination of the dipole moment and of the quadrupole coupling constants gave values which were not in good agreement with those predicted from nonhydrogen bonded molecules. In addition a value V 3 = 3100 ± 100 cal/mol was calculated for the CH 3 torsional barrier in the related 2-methoxyethanol, using previous experimental data ( Canad. J. Chem. 50, 1149–1156 (1972)).