Portal de Periódicos da CAPES

Experimental and theoretical estimates of the internal rotational barrier of benzyl fluoride in the vapor phase

1990; NRC Research Press; Volume: 68; Issue: 4 Linguagem: Inglês

10.1139/v90-089

1480-3291

Ted Schaefer, Christian Beaulieu, Rudy Sebastian, Glenn H. Penner,

Advanced Physical and Chemical Molecular Interactions

The twofold barrier to rotation about the [Formula: see text] bond in benzyl fluoride is deduced from the long-range 1 H, 1 H; 1 H, 19 F; and 13 C, 19 F nuclear spin–spin coupling constants in solution. The barrier changes from 3.2(2) kJ/mol in the polar solvent, acetonitrile-d 3 , to 0.7(2) kJ/mol in the nonpolar environment provided by cyclohexane-d 12 . In all solutions the conformer of greatest stability has the C—F bond in a plane perpendicular to that of the phenyl group. Extrapolation of the barrier to the vapor phase, using a simple reaction field model, indicates that the most stable conformer for the free (unclustered) molecule is now that with the C—F bond in the phenyl plane and that the barrier to internal rotation is 1.1(7) kJ/mol. Molecular orbital calculations with the basis sets STO-3G, 4-21G, 4-31G, 6-31G, and 6-31G* all predict the latter conformer as that of lowest energy. However, they disagree significantly among themselves as to the height of the internal barrier. The complete geometries are given for both conformers, as computed with the 6-31G basis, and the side-chain geometries are tabulated for the planar and perpendicular conformers, as given by all the bases. Keywords: benzyl fluoride, internal rotational potential; 13 C, 19 F spin–spin coupling constants in benzyl fluoride; benzyl fluoride, molecular orbital computations.