Reactions of radicals. XXVI. On the use of activation parameters as a test for concerted decomposition of initiators

Abstract

Abstract In 1958, Bartlett and Hiatt [1] suggested that the number of bonds which are rotationally “frozen” at the transition state for decomposition of peresters can be determined from the magnitude of the values of Δ H ‡ and Δ S ‡ . In recent years, other workers have extended this hypothesis to include the use of the magnitude of Δ H ‡ and Δ S ‡ values to determine the number of bonds which undergo synchronous scission in the decomposition of initiators. This criterion for separating one‐bond from two ‐or three‐bond initiators is discussed in the light of all of the data now reported in the literature. It is probable that the correlation of Δ H ‡ and Δ S ‡ in an isokinetic plot cannot be used to distinguish either the number of bonds which are rotationally frozen at the transition state or the number that are undergoing scission, except in limited and rather imprecise ways. However, the insights and principles of Bartlett and Hiatt still are extremely useful as qualitative tools.