Evidence for intramolecular OH...p hydrogen bonding in unsaturated alcohols from UV photoelectron spectroscopy.
In: Journal of Molecular Structure (J.Mol.Struct.), Jg. 567-568 (2001), S. 231-240
Zeitschriftenaufsatz / Fach: Chemie
The gas phase He(I) photoelectron (PE) spectra of several unsatd. alcs. have been measured and analyzed with respect to intramol. OH...p hydrogen bonding. Evidence for such a hydrogen bond has been detected in the spectra of 2-allylphenol (I) and 2-phenylethan-1-ol (II). I exists as a conformational mixt. of a hydrogen bonded form (III) and an open form (IV) in a compn. of roughly 2:1. A strong ionization band (IPv = 10.01 eV; where IPv is the vertical ionization potential) is assigned to the ethylenic C=C double bond in the major conformer III and a weak band (IPv = 9.72 eV) to that of the minor conformer IV. The latter IP coincides with the corresponding ionization of allylbenzene. In the series of w-phenylalkan-1-ols, II exhibits an unusually low np(O) ionization indicating hydrogen bonding between the OH group and the p electron system of the Ph ring. The higher homologs prefer \"open\" conformations without such interaction. The PE spectra of alkenols such as but-3-en-1-ol and pent-4-en-1-ol as well as of alkynols such as but-3-yn-1-ol and pent-4-yn-1-ol are consistent with OH...p hydrogen bonded conformers. The methanol/ethylene heterodimer has a T-shaped structure, as indicated by B3LYP/6-311++G(d) calcns., with a binding energy of 5.65 kJ mol-1.