4848-85-5Relevant academic research and scientific papers
Phenyl Effects in Radical Additions to Alkenes
Giese, Bernd,Kretzschmar, Gerhard
, p. 3267 - 3270 (2007/10/02)
Reactions of cyclohexylmercuric salts 4 with NaBH4 in the presence of alkenes 8 yield products 10.The main step of the reaction sequence, the addition of a cyclohexyl radical (7) to alkene 8, can be measured using a competition technique.The data show that styrene reacts 30 - 40 times faster than expected by the ?p--value.This phenyl effect decreases in going from monosubstituted alkenes 8 to disubstituted alkenes 3, 2 and 1 because the steric hindrance of a coplanar orientation of the ?-system increases in the same order.
Selectivity of prim., sec. and tert. Alkyl Radicals in Addition Reactions
Giese, Bernd,Kretzschmar, Gerhard,Meixner, Juergen
, p. 2787 - 2795 (2007/10/02)
In reductions of alkylmercuric salts 4 and 5 with NaBH4 alkyl radicals 1 are formed as intermediates.The selectivity of prim., sec. and tert. radicals in addition reactions with alkenes 6-12 can be measured by this "mercury-method", because adduct radicals 13-19 form products 20-26 quantitatively.Dimerization, disproportionation, polymerization, trapping of oxygen and β-bond cleavage don't compete with the hydrogen transfer to 13-19.The measurements show, that alkyl radicals 1 are nucleophiles and that their selectivity increases in going from prim. to sec. and tert. radicals (Table 1).As long as steric effects are not important, reactivities and selectivities can be described by frontier molecular orbital theory.As a consequence of this theory selectivity increases with increasing reactivity.
