Absolute Rate Constants for Hydrocarbon Autoxidation. XXI. Activation Energies for Propagation and the Correlation of Propagation Rate Constants with Carbon–Hydrogen Bond Strengths

Abstract

The rate constants, k,, for the abstraction of a hydrogen atom from a wide variety of organic substrates at 30" have been correlated with the strengths of the C-H bond that are broken, D[R-HI (in units of kcal/mol). Two empirical relations have been derived, one for tertiary peroxy radicals,and one for secondary peroxy radicals,These equations hold extremely well for hydrocarbons and reasonably well for substrates containing heteroatoms. The activation energies and pre-exponential factors for the oxidation of some hydrocarbons by I-butylperoxy radicals have been measured and the empirical relation derived. If D[I-ROO-H] is taken as 88 kcal/mol, this yields the Polanyi equation,where AH is the heat of the hydrogen abstraction reaction. These empirical equations permit the calculation of the rate constants for chain propagation in the autoxidation of many organic substrates at 30' and also at other temperatures.

Mammalian sperm metabolism: oxygen and sugar, friend and foe

“…The most striking characteristic of spontaneous lipid peroxidation as observed in these cells is the high activation energy (E A ) of 79 kcal/mol (330 kJ/mol). This value is close to that of 80 kcal/mol determined for the bond energy of the C-H bond of an allylic methylene CH 2 group (Korcek et al, 1972), a group characteristic of the PUFA acyl moieties. The high value of E A confers an advantage in storage stability on sperm in the epididymis of mammals with scrota: the rate of spontaneous lipid peroxidation at a scrotal temperature of 30 o C should be some sixfold lower than the rate at 37 o C.…”

Degradation behavior of polymer blend of isotactic polypropylenes with and without unsaturated chain end group

“…Among these reaction steps, the hydroperoxide decompositions (IV) and/or (V) are the rate-determining steps [4,20,21]. The Es obtained here corresponds to those of the hydroperoxide decomposition [20].…”

A Radical Account of “Oxygenated Fenton Chemistry” 1

“…It is totally unnecessary to invoke catalyst "turnover" to explain these results since they can be simply accounted for on the basis of the relative importance of reaction 5. For cyclohexane, 11 ethylbenzene, 12 and cyclohexene, 12 the values for k5 are 0.048, 1.1, and 6.1 M -1 s -1 , respectively. Thus, reaction 5 is insignificant for cyclohexane, is relevant for ethylbenzene, and becomes important for cyclohexene.…”