Thermochemistry of alkyl free radicals

The group additivity difference method is used to estimate the thermochemical properties (Cp0(T), 298 < T/K <1000, S0298, ΔfH0298) of alkyl free radicals from ethyl through the C6 radicals. Revised values are calculated for the alkyl radical groups. Recent experimental and theoretical work on hindered rotor barrier heights necessitating these revised calculations is discussed. All Cp's are also expressed in polynomial form, Cp0(T) = a1 + a2T + a3T2 + a4T3. Polynomial coefficients are given for the calculation of the equilibrium constants for formation of the radicals from the elements: nC + 1/2(2n + 1)H2 ↔ CnH2n+1. 35 refs., 12 tabs