The nucleophilic silyl radical: Dual-Parameter correlation analysis of the relative rates of bromine-atom abstraction reactions as measured by a rigorous methodology

Article abstract of DOI:10.1016/S0040-4020(97)00527-9

The relative rates [k(R)(Y) values] of bromine-atom abstraction reactions of 13 p-Y-substituted benzyl bromides (1Y's : Y = H, Et, tBu, Me₃Si, MeS, Ph, P, Cl, Br, CF₃, CN, CO₂Me,SO₂Me) by tris(trimethylsilyl) silyl radicals [(Me₃Si)₃Si^.] in cyclohexane at 80°C have been measured by a rigorous methodology. Correlation analysis of the kinetic data by the dual-parameter equation (log k(H)/k(H) = ρ(x)σ(x)+ρ^.σ^.) shows that the silyl radical is distinctly nucleophilic and the transition states of the bromine-atom abstraction reactions are affected by both the polar and spindelocalization effects of the Y-substituents. Comparison of the |ρ(p) / ρ(jj)^.| values suggests that the contribution of the spin-delocalization effects in this Br-atom abstraction reaction may be greater than the spin-delocalization effects in some H-atom abstraction reactions.