ON THE PLANARITY OF STYRENE AND ITS DERIVATIVES - THE MOLECULAR-STRUCTURES OF STYRENE AND (Z)-BETA-BROMOSTYRENE AS DETERMINED BY AB-INITIO CALCULATIONS AND GAS-PHASE ELECTRON-DIFFRACTION

The molecular structures of styrene and (Z)-beta-bromostyrene have bee n studied in the pas phase at nozzle temperatures of 303 and 338 K res pectively. For both molecules the electron diffraction data were consi stent with the results from ab initio calculations which described the vinyl torsional motion, near the planar configurations, in terms of a double minimum potential function with barriers of 243 cal mol(-1) (s tyrene) and 430 cal mol(-1) (bromostyrene) at the planar form, and wit h the minimum energy forms 27 degrees (styrene) and 39 degrees (bromos tyrene) away, The perpendicular barriers were calculated to 2.73 kcal mol(-1) (styrene) and 1.10 kcal mol(-1) (bromostyrene). The important distances (r(a)) and angles (angle(alpha)) obtained from least squares refinements of the electron diffraction data are as follows: styrene, r(C-H)(Av) = 1.102(7) Angstrom, r(C=C) = 1.355(16) Angstrom, r(C-C)(P h) = 1.399(2) Angstrom, r(C-C=) = 1.475(23) Angstrom, angle C=C-C = 12 6.9(24)degrees; and bromostyrene, r(C-H)(Av) = 1.082(13) Angstrom, r(C =C) = 1.331(20) Angstrom, r(C-C)(Ph) = 1.400(2) Angstrom, r(C-C=) = 1. 465(20) Angstrom, r(C-Br) = 1.893(8) Angstrom, angle C=C-C = 132.8(23) degrees, angle Br-C=C = 125.7(15)degrees, angle C-2-C-1-C-7 = 123.9(33 ). (C) 1997 Elsevier Science B.V.