Microwave Spectrum, Dipole Moment, and Intramolecular Hydrogen Bond of 2-Methoxyethanol

The minimum energy conformation of 2-methoxyethanol (CH 3 OCH 2 CH 2 OH) has been determined from an analysis of its microwave spectrum. The rotational constants of the normal species are: A = 12982.35, B = 2742.48, and C = 2468.10 MHz; the dipole moment components are μ a = 2.03, μ b = 1.15, [Formula: see text] and μ = 2.36 ± 0.03 D. For the CH 3 OCH 2 CH 2 OD species: A = 12385.71, B = 2724.74, and C = 2431.42 MHz. The conformation consistent with this data is gauche about each of the C—C, C—O(H) and C—O(ether) bonds, having dihedral angles of 57 ± 3°, 45 ± 5°, and 8 ± 3°, respectively. This distorted conformation is one in which the hydroxyl hydrogen atom is approximately aligned with the nearest sp 3 lone pair electrons of the ether oxygen atom. Transitions in three excited torsional states have also been observed but no other rotational isomer was detected.