A KINETIC, PRODUCT AND KINETIC ISOTOPE EFFECT INVESTIGATION OF THE BROMINATION OF 1,1-DIPHENYLETHYLENES AND OF THEIR 2,2-DIDEUTERIO DERIVATIVES

The kinetics of bromination of 1,1-diphenylethylene(1a), 4-trifluorome thyl-1,1-diphenylethylene(1b), and hylphenyl)-1-(4-trifluoromethylphen yl)ethylene(1c) and of their 2,2-dideuterio derivatives have been inve stigated in 1,2-dichlorodthane. The rate law was always second-order i n Br-2 and first-order in olefin, with the following k(3): 1a (L=H), 1 .7(0.1) x 10(7); 1b (L = H), 8.0 (0.1) x 10(4); 1c (L = H), 52 (2) dm( 6) mol(-2) s(-1). Olefin 1a (L = H) gave dibromide 4a and vinyl bromid e 3a in a ratio changing from 99:1 at 10(-2) mol dm(-3) to 5:95 at 10( -4) mol dm(-3) Br-2 and olefin. The k(3) was independent of the reagen t concentrations and of the extent of proton loss from the intermediat e, showing that the last step was not rate limiting and the formation- of the intermediate-was completely rate determining. In the whole inve stigated concentration range, only dibromides 4b and 4c were instead o btained from Ib and Ic,:respectively. A negligible KIE, 0.97 (0.01) wa s found for 1a, whether the dibromide or the vinyl bromide was the mai n product, while significant inverse KIEs were obtained for 1b, 0.75 ( 0.05), for 1c, 0.70 (0.05), on deuteriation of the methylene group, an d for cis-1,2-diphenylethylene,2. The kinetic and product distribution data are discussed in terms of nature of the intermediates,: dependin g on substituent effect and reagent concentration.