Very Low Pressure Pyrolysis of Phenylacetic Acid

Recent reviews on the thermochemistry of organic radicals in the gas phase,'*2 have pointed out the necessity of a reassessment of the heat of formation of the hydroxycarbonyl radical and the corresponding bond-dissociation energy Ed in formic acid. Based on a re-evaluation of the early work of Back and S e h ~ n , ~ McMillen and Golden,' have recommended A,H('CO,H) = -209.2 kJ mol-'; however, standard correlations between C--H stretching frequencies and bonddissociation energies indicate a stronger In order to bring some progress to this issue, we decided to reinvestigate the thermolysis of phenylacetic acid at very low pressures, conditions that would effectively isolate the primary step :