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 been studied in the pas phase at nozzle temperatures of 303 and 338 K respectively. For both molecules the electron diffraction data were consistent 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) (styrene) and 430 cal mol(-1) (bromostyrene) at the planar form, and with the minimum energy forms 27 degrees (styrene) and 39 degrees (bromostyrene) 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)(Ph) = 1.399(2) Angstrom, r(C-C=) = 1.475(23) Angstrom, angle C=C-C = 126.9(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.