Heats of Formation of Some Simple Alkyl Radicals

Article abstract of DOI:10.1021/ja00377a018

Equilibrium constants, K, for the system Me<*> + RI <*> MeI + R<*> were measured in solution by using electron paramagnetic resonance spectroscopy.Given the entropies of the components of the equilibrium and the heats of formation of the iodides, the relative heats of formation of the alkyl radicals were obtained.With δH_f,300(Me<*>) = 34.4 kcal mol^-1 chosen as a standard, the following heats of formation for other alkyl radicals were obtained: Et<*>, 28.0; n-Pr<*>, 22.8; i-Pr<*>, 19.2; s-Bu<*>, 13.9; c-C5H9<*>, 25.1; t-Bu<*>, 9.4 kcal mol^-1.These data lead to the following C-H bond dissotiation energies for simple alkanes: primary C-H, ca. 100; secondary C-H, ca. 96; tertiary C-H, ca. 94 kcal mol^-1.