THE ANOMERIC EFFECT IN TRIFLUOROMETHOXY METHANE, CF3OCH3

The molecular structure of trifluoromethoxy methane was determined by a joint analysis of gas diffraction intensities and rotational constan ts, incorporating a normal coordinate analysis, in order to test the p redictions of the stereoelectronic effects model, the generalized anom eric effect. Due to the internal rotation of the methyl group, some li nes were split and the torsional barrier, V-3(CH3) = 382 (10) cm(-1), could be determined. The rotational constants are: B-0 = 3069.253 (48) and C-0 = 3045.581 (48) MHz. Ab initio calculations at different leve ls of theory helped to interpret the data. The following structural pa rameters were derived (r(a) parameters in Angstrom and bond angles in degrees): O-C-H: 1.426 (9); O-C-F: 1.347 (9); C-F-t: 1.318(7); C-F-g: 1.336 (5); (C-H)(mean): 1.095 (24); COC: 115.5(4); (FCF)(mean): 107.7 (4); (HCH)(mean): 111.1(19); OCFt: 109.0 (8); OCFg: 112.3 (7). The str ucture fully confirms the predictions of the anomeric effect model.