Direct observation of carbon-carbon bond fragmentation in .alpha.-amino alcohol radical cations
作者:Lucian A. Lucia、Richard D. Burton、Kirk S. Schanze
DOI:10.1021/j100138a002
日期:1993.9
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) x 10(5) s-1, DELTAH(BF)double dagger(e-1.+) = 7.6 (1) kcal, DELTAS(BF)double dagger(e-1.+) = -9 (4) em; k(BF)(t-1.+) = 2.6 (1) x 10(5) s-1, DELTAH(BF)double dagger(t-1.+) = 4.8 (1) kcal, DELTAS(BF)double dagger(t-1.+) = -19 (4) eu. Fragmentation of e-1.+ is catalyzed by a series of substituted pyridines. A linear Bronsted correlation (log k(base) vs pK(a), beta = 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.