Thermodynamic and kinetic properties of the cyclohexadienyl radical

The experimental data on cyclohexadienyl (1,3-cyclohexadien-5-yl) radical decomposition have been examined. In combination with an estimated entropy for cyclohexadienyl of 375 +/- 7 J/(Kmol) at 550 K, and the measured rates of hydrogen addition to benzene and the reverse the authors find the heat of formation of cyclohexadienyl to be 209 +/- 5 kJ/mol (300 K). This leads to k(cyclohexadienyl ..-->.. benzene + H) = 10/sup 13.3 +/- 0.6/ exp(-13,100 +/- 700/T)/s in the vicinity of 550 K. The HC-H bond energy in cyclohexadiene is 318 kJ, leading to a resonance energy of 96 kJ. The second-order disappearance rate of cyclohexadienyl radical at 425 K has been found to be 7 x 10/sup -11/ cm/sup 3//(molecule s). This is in excellent agreement with direct measurements at room temperature. 20 references, 1 figure, 3 tables.