Far infrared spectra, conformational equilibria, vibrational assignments, ab initio calculations and structural parameters for 2-bromoethanol

The far infrared spectrum from 370 to 50 cm(-1) of gaseous 2-bromoethanol, BrCH2CH2OH, was recorded at a resolution of 0.10 cm(-1). The fundamental O- H torsion of the more stable gauche (Gg') conformer, where the capital G re fers to internal rotation around the C-C bond and the lower case g to the i nternal rotation around the C-O bond, was observed as a series of Q-branch transitions beginning at 340 cm(-1). The corresponding O-H torsional modes were observed for two of the other high energy conformers, Tg (285 cm(-1)) and Tt (234 cm(-1)). The heavy atom asymmetric torsion (rotation around C-C bond) for the Gg' conformer has been observed at 140 cm(-1). Variable temp erature (-63 to - 100 degreesC) studies of the infrared spectra (4000-400 c m(-1)) of the sample dissolved in liquid xenon have been recorded. From the se data the enthalpy differences have been determined to be 411 +/- 40 cm(- 1) (4.92 +/- 0.48 kJ/mol) for the Gg'/Tt and 315 +/- 40 cm(-1) (3.76 +/- 0. 48 kJ/mol) for the Gg'/Tg, with the Gg' conformer the most stable form. Add itionally, the infrared spectrum of the gas, and Raman spectrum of the liqu id phase are reported. The structural parameters, conformational stabilitie s, barriers to internal rotation and fundamental frequencies have been obta ined from ab initio calculations utilizing different basis sets at the rest ricted Hartree-Fock or with full electron correlation by the perturbation m ethod to second order. The theoretical results are compared to the experime ntal results when appropriate. Combining the ab initio calculations with th e microwave rotational constants, ro adjusted parameters have been obtained for the three 2-haloethanols (F, Cl and Br) for the Gg' conformers. (C) 20 01 Elsevier Science B.V. All rights reserved.