A flowing afterglow/selected ion flow tube instrument has been used to measure the rates of reaction of amide ion with benzene and phenide ion with ammonia C[sub 6]H[sub 6] + NH[sub 2][sup +] = C[sub 6]H[sub 5] + NH[sub 3]. The ratio of these rate constants gives a free energy change. [Delta][sub reaction]G[sub 300] = 3.58 [+-] 0.06 kcal mol[sup [minus]1]. Use of the established gas-phase acidity of ammonia gives a value for [Delta][sub acid]G[sub 300](C[sub 6]H[sub 6]) of 392.9 [+-] 0.4 kcal mol[sup [minus]1]. From the computed value for [Delta][sub acid]S[sub 300](C[sub 6]H[sub 6]) of 29.6 [+-] 1.0 cal mol[sup [minus]1] K[sup [minus]1], the enthalpy change, [Delta][sub acid]H[sub 300](C[sub 6]H[sub 6]) = 401.7 [+-] 0.5 kcal mol[sup [minus]1], is derived. The enthalpy of deprotonation of benzene, the C-H bond dissociation energy, and the electron affinity of the phenyl radical are simply related to each other. [Delta][sub acid]H[sub 300](C[sub 6]H[sub 6]) = DH[sub 300](C[sub 6]H[sub 5]-H) + IP(H) [minus] EA(C[sub 6]H[sub 5]). Since earlier photoelectron experiments have provided a value for the electron affinity for the phenyl radical, EA-(C[sub 6]H[sub 5]) = 25.3 [+-] 0.1 kcal mol[sup [minus]1] the enthalpy of deprotonation can be used to extract a value formore » the C-H bond enthalpy of benzene at 300 K and the C-H bond energy at 0 K, D[sub 0]. These bond energies are used to compute the heats of formation of the phenyl radical at 0 and 300 K. 65 refs., 3 tabs.« less