Microwave spectra of isotopic glycolaldehydes, substitution structure, intramolecular hydrogen bond and dipole moment

• Published in: Journal of molecular structure 1973-01, Vol.16 (2), p.259-270
• Main Authors: Marstokk, K.-M., Møllendal, Harald
• Format: Article
• Language: English
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/0022-2860(73)80065-1

The microwave spectra of 13CH 2OH-CHO, CH 2OH- 13CHO, and CH 2OH-CH 18O are reported and have been used in combination with previously published data on other monosubstituted glycolaldehydes to determine the substitution structure of the molecule as r(CO) = 1.209 Å, r(C-O) = 1.437 Å, r(C-C) = 1.499 Å, r(O-H) = 1.051 Å, r(C-H ald) = 1.102 Å, r( C-H alc) = 1.093 Å, r(O β H) = 2.007 Å, r(O β O) = 2.697 Å, ∠(C-CO) = 122°44', ∠(C-C-H ald) = 115°16', ∠(C-C-O) = 111°28', ∠(C-O-H) = 101°34', ∠(C-C-H alc) = 109°13', ∠(H-C-H) = 107°34', ∠(O-H β O) = 120°33', ∠(H β OC) = 83°41', and ∠(O-H, C0) = 24°14'. The intramolecular hydrogen bond and the other structural parameters are discussed and compared to related molecules. The dipole moment is redetermined to be μ a = 0.262 ±0.002 D, μ b = 2.33 ± 0.01 D, and μ tot = 2.34 ± 0.01 D. Relative intensity measurements yielded 195 ± 30 cm −1 for the C-C torsional fundamental and 260±40 cm −1 for the lowest in-plane skeletal bending mode. Computations performed by the CNDO/2 method correctly predict the observed cis hydrogen-bonded conformer to be the energetically favoured one and in addition yield some indication of the existence of at least two other non-hydrogen-bonded forms of higher energy.