Radical equilibrium studies; the thermodynamic parameters of n-propyl

A novel method for the investigation of the thermodynamic properties of free radicals is described. It involves the establishment of an equilibrium of the form where R₁ and R₂ are free radicals, and the measurement of the recombination products of R₁ and R₂. The method is applied to the case where R₁ is n-propyl, R₂ is methyl, and the olefin is ethene, using the thermal decomposition of azomethane (a source of methyl) in the presence of ethene in the temperature range of 581–649°K. Using the best available thermodynamic parameters for methyl, it is concluded that those for n-propyl are in need of adjustment. We recommend the values ΔH_f°(300°K) = 22.6 ± 1 kcal/mol and S₃₀₀° = 67.4 ± 3 cal/mol · K together with either the heat capacity data of O'Neal and Benson or the essentially identical data derivable from the results of Purnell and Quinn.