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

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Abstract
The minimum energy conformation of 2-methoxyethanol (CH3OCH2CH2OH) 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 μa = 2.03, μb = 1.15, [Formula: see text] and μ = 2.36 ± 0.03 D. For the CH3OCH2CH2OD 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 sp3 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.

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