Bifurcated Hydrogen Bonding in 2-Trifluoromethylphenol Confirmed by Gas Electron Diffraction

Abstract

The molecular structure of 2-trifluoromethylphenol has been determined by gas-phase electron diffraction. The analysis, aided by constraints from ab initio molecular orbital calculations, yielded the following bond lengths ( r g ) and bond angles: (C−C) Ar,mean, 1.395 ± 0.004 Å; C−C(F 3 ), 1.510 ± 0.005 Å; C−O, 1.362 ± 0.011 Å; (C−F) mean, 1.358 ± 0.006 Å; ∠O−C 1 −C 2, 121.0 ± 1.2°; ∠C−O−H, 105 ± 6°; ∠C(F 3 )−C 2 −C 1, 120.7 ± 0.8°; (C−C−F) mean, 113.2 ± 0.3°; CF 3 torsion, 10.1 ± 0.8°. Weak intramolecular bifurcated hydrogen bonding between the hydroxy hydrogen and two of the CF 3 fluorines is indicated by the H···F nonbonded distances 2.05 ± 0.06 and 2.42 ± 0.06 Å. Compared with the freely rotating CF 3 group in trifluoromethylbenzene, the well-defined conformer of 2-trifluoromethylphenol indicates the constraining effect of hydrogen bonding.