Thermochemistry of the benzyl and allyl radicals and ions

We have studied the thermochemistry of the resonantly stabilized radicals, C6H5CH2 and CH2CHCH2 and their corresponding cations and anions. A flowing afterglow/selected ion flow tube instrument has been used to measure the rates of reaction: C6H5CH3 + CH3O- reversible arrow C6H5CH2- + CH3OH C6H5CH3 + CD3O- reversible arrow C6H5CH2- + CD3OH C6D5CD3 + CH3O- reversible arrow C6D5CD2- + CH3OD C6D5CD3 + CD3O- reversible arrow C6D5CD2- + CD3OD CH2CHCH3 + HO- reversible arrow CH2CHCH2- +H2O The ratio of the rate constants gives a free energy change for each reaction and use of the established gas phase acidity of CH3OH or H2O provides values for the acidities. We calculate the entropy changes, Delta(acid)S(300)(C6H5CH3) and Delta(acid)S(300)(CH2CHCH3), to extract values for Delta(acid)H(300)(C6H5CH3) and Delta(acid)H(300)(CH2CHCH3). Earlier photoelectron experiments have provided ionization potentials and electron affinities for the benzyl and allyl radicals. Use of the IPs and EAs, together with the enthalpies of deprotonation, provides values for the C-H bond enthalpies at 300 K and the C-H bond energies at 0 K. These bond energies are used to compute the heats of formation of the radicals and ions as well as the cation hydride affinities, HA (all values in kcal mol(-1)): [GRAPHICS] In addition, we find Delta(acid)G(300)(C6D5CD3) = 377.0 +/- 0.3 kcal mol(-1).