MOLECULAR-STRUCTURE OF TETRAFLUOROHYDROQUINONE AND GEOMETRICAL INDICATION OF INTRAMOLECULAR HYDROGEN-BONDING FROM GAS-PHASE ELECTRON-DIFFRACTION

The molecular structure of tetrafluorohydroquinone has been determined by electron diffraction in the gas phase. The molecular geometry indicates possible formation of a weak intramolecular hydrogen bond between the OH and F substituents in ortho positions. The nearest H...F and O...F interactions, at 2.02 +/- 0.07 and 2.66 +/- 0.05 angstrom are closer than the sums of van der Waals radii, 2.55 and 2.75 angstrom respectively. The C-OH and C-F bonds are somewhat tilted towards each other. The C-O-H angle, 98 +/- 2-degrees, is smaller than in hydroquinone. The C-O bond, (r(g)), 1.353 +/- 0.009 angstrom is shorter than in phenol and in hydroquinone. The ring parameters are r(g)(C-C)mean 1.394 +/- 0.003 angstrom, angle C-C(OH)-C = 117.0 +/- 0.5-degrees, (angle C-C(F)-C)mean. = 121.5 +/- 0.2-degrees. The angular ring deformation corresponds to additivity of the individual substituent effects with no appreciable consequence of substituent interaction within experimental error. The mean C-F bond length (r(g)) is 1.346 +/- 0.005 angstrom. A mixture of two conformers with C-2v and C2h symmetry is likely.