EQUILIBRIUM-CONSTANT AND RATE CONSTANT FOR ALLYL RADICAL RECOMBINATION IN THE GAS-PHASE

The equilibrium and recombination 2 allyl ⇄1, 5-hexadienc at (T) = 950 K and the recombination reactionat T=625 K have been studied in a VLPP (very low-pressure pyrolysis) apparatus. The van't Hoff plot yields In Kr, d/M-1:= (-34.56 + 10.60)/R+(56 100/RT), which gives ΔH°f(allyl) = 39.1 ± 1.5 kcal/mol, a bond dissociation energy BDE(C3H5-H) = 86.3 ± 1.5 kcal/mol, and an allyl resonance energy ARE = 11.7 ± 2.0 kcal/mol. The recombination rate constant Krat 〈T〉 = 900 K is found to be (1.90 ± 0.80) X 109 M-1s-1, and at T = 625 K, kris(6.50± 1.0) X 109M-1s-1. RRKM calculations indicate a degree of fall-off kr/kr∞ = 0.37 at 625 K and 0.045 at 900 K. © 1979, American Chemical Society. All rights reserved.