GAS-PHASE ELECTRON-DIFFRACTION STUDY OF THE MOLECULAR-STRUCTURE OF 1,1,2-TRIFLUOROETHANE, ASSISTED BY CALCULATION OF THE VIBRATIONAL AMPLITUDES FOR 1,2-DIFLUOROETHANE FROM SPECTROSCOPIC DATA

被引:26
作者
BEAGLEY, B
BROWN, DE
机构
[1] Department of Chemistry, University of Manchester Institute of Science and Technology, Manchester, M60 1QD, Sackville Street
关键词
D O I
10.1016/0022-2860(79)80065-4
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The gas phase conformational mixture of the rotamers of 1,1,2-trifluoroethane has been subjected to an electron diffraction study at 265 K. The radial distribution curve has a peak at 3.5 Å attributable to an anti F ... F distance, indicating a predominance of the conformer possessing this distance. Effective least-squares refinement of the geometry and the relative proportions of the conformers was achieved with vibrational amplitudes for both conformers fixed at values derived from spectroscopic data for 1,1,2,2-tetra- and 1,2-di-fluoroethane. The amplitudes for the latter molecule were calculated from an optimised force field which reproduced the observed wavenumbers for both of its conformers. For 1,1,2-trifluoroethane at 265 K, the conformer with the F ... F anti distance was found to be present in 92% abundance, which corresponds to an energy difference between conformers of 900 cal mol-1. The geometrical parameters (ra values) and e.s.d. are CC = 1.500 ± 0.005 Å, CH(mean) = 1.088 ± 0.011 Å, CF(CF2H gp) = 1.353 ± 0.004 Å, CF(CH2F gp) = 1.387 ± 0.008 Å, ∠CCF(mean) = 109.0 ± 0.5°, ∠CCH(mean) = 108.9 ± 1.4°, ∠FCF = 106.8 ± 0.7°. As in 1,2-difluoroethane ∠HCH ≈ 120°. The τHCCF torsional angles of the predominant F ... F anti conformer are 38, 47, 56 and 78°, τHCCH = 66° and τFCCF = 75°. © 1979.
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页码:175 / 184
页数:10
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