Direct Observation of C-C Bond Fragmentation in α-Amino Alcohol Radical Cations

Article abstract of DOI:10.1021/j100138a002

The kinetics of heterolytic fragmentation of the 1,2 C-C bond in the radical cations of erythro- and threo-2-(N-phenylamino)-1,2-diphenylethanol (e-1 and t-1, respectively) have been directly determined by using laser flash photolysis.The 298 K rates and activation parameters are as follows (CH3CN solution): k_BF(e-1^.+)=4.3(1)x10⁵ s^-1, ΔH(excit.)_BF(e-1^.+)=7.6(1) kcal, ΔS(excit.)_BF(e-1^.+)=-9(4) em; k_BF(t-1^.+)=2.6(1)x10⁵ s^-1, ΔH(excit.)_BF(t-1^.+)=4.8(1) kcal, ΔS(excit.)_BF(t-1^.+)=-19(4) eu.Fragmentation of e-1^.+ is catalyzed by a series of substituted pyridines.A linear Broensted correlation (log k_base vs pK_a, β=0.62) indicates that under base-catalyzed conditions endothermic H⁺ transfer from e-1^.+ to base is the rate-determining step for C-C bond fragmentation.