RADICAL INTERMEDIATES IN THE ADDITION REACTION OF SECOND ROW RADICALS TO STILBENE AND 2-BUTENE. AN ESR STUDY

Article abstract of DOI:10.1016/S0040-4020(01)91982-9

The adducts of stilbene with triphenylsilyl, triphenylgermyl, diethoxyphosphonyl and phenylthiyl radicals, and of 2-butene with triethylsilyl and ethylthiyl radicals have been generated and their ESR spectra recorded.The resulting radical adducts show the same ESR spectrum starting either from the cis or the trans isomer of the title compounds.The existence of only one isomeric radical is consistent with the lack of stereospecificity in the elimination reaction of phenylthiyl radicals from 2-phenylthiobutyl. The magnitude of the β-proton hyperfine splittings is indicative for a geometry where the entering group eclipses the 2p_z orbital on the radical carbon centre in the adducts with 2-butene.In the adducts with stilbene, on the other hand, the experimental data suggest a certain departure from a perfectly eclipsed conformation.Since the extent of this deviation decreases in the order SiPh3 > GePh3 > P(O)(OEt)2 > SPh, sterical crowding seems to be responsible for this behaviour.