Abstract
An absolute kinetic scale for amidyl radical reactions was established by a combination of direct laser flash photolysis (LFP) and indirect competition kinetic studies. Six amidyl radicals were studied by LFP. Arrhenius parameters were determined for 6-exo cyclizations of the N-butyl-6,6-diphenyl-5-hexenamidyl radical (2) and the N-butyl-6-(trans-2-phenylcyclopropyl)-5-hexenamidyl radical (5) and for 1,5-hydrogen transfer in the N-(6,6-diphenyl-5-hexenyl)acetamidyl radical (3); rate constants for these reactions at 20 °C are 3.0 × 107 s-1 (2), 5.5 × 106 s-1 (3), and 1 × 107 s-1 (5). Kinetic limits were established by LFP for the fast cyclizations of the N-methyl-5,5-diphenyl-4-pentenamidyl radical (1) and the N-methyl-5-(trans-2-phenylcyclopropyl)-4-pentenamidyl radical (4) (k > 2 × 108 s-1 at ambient temperature) and for the slow fragmentation of the N-(2,2-diphenylethyl)acetamidyl radical (6) (k = 2 × 104 s-1 at 48 °C). Rate constants for amidyl radical reactions with Bu3SnH and PhSH were determined by ...
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