Comparison of Radical and Nonradical Processes in the Condensed-Phase Radiolysis of n-Hexadecane

Abstract

The effects of state, temperature, and chemically reactive solutes on the radiolysis of n‐hexadecane in condensed phases have been examined. All product yields are reduced by radical scavengers in liquid‐state n‐hexadecane, but only dotriacontane isomers are reduced in the solid. Iodine acts as a chemical scavenger and is more effective than 2‐methylpentene−1. A hot‐hydrogen‐atom mechanism, together with molecular elimination, accounts for the formation of most of the hydrogen in the irradiation of n‐hexadecane. Low‐molecular‐weight products are formed entirely by molecular reactions in the solid‐state radiolysis and, about equally, via molecular and radical processes in the liquid. Intermediate‐molecular‐weight products in the liquid radiolysis are 80% from combinations of radicals from chain scission with various hexadecyl radicals. The remaining 20% in the liquid and the total intermediate yield in the solid are from nonradical processes. The combination of hexadecyl radicals yields at least 40% and 70% of the dotriacontane isomers in the radiolysis of pure n‐hexadecane in the solid and liquid state, respectively. The remaining dimer may also be due to radicals which are formed in pairs, but ion—molecule reactions cannot be excluded. Temperature dependence of all products is small. Cage recombination of scission fragments and crosslinking of proximate radical pairs is enhanced in the solid state as compared with the liquid. Internal ···CH₂–CH₂··· rupture is equally probable at all positions, and seven times as likely as terminal CH₃–CH₂··· scission. Methyl C–H rupture is 40% as probable per bond as methylene C–H rupture.