The C-H Bond Energy of Benzene

Studies of the Kinetics and Thermochemistry of the Forward and Reverse Reaction Cl + C6H6 = HCl + C6H5

“…These results check recent revisions to the C 6 H 5 -H bond dissociation enthalpy D 298 , which are based on the ion chemistry of Davico et al 7 and the interpretation of several kinetic experiments by Heckmann et al 8 A negative activation energy E a is found for eq -1. Negative E a values have been observed earlier in the case of alkyl and silyl radical reactions with HBr and HI, [9][10][11][12][13][14] although these experiments have been criticized.…”

“…For comparison, a recent assessment is 474.9 ( 2.5 kJ mol -1 . 7 Therefore, the Shi and Bernhard rate constant appears somewhat too high, and we employed the Sokolov et al value in our recommendation for k 1 above. This k 1 and our k -1 yield ∆ f H 298 (C 6 H 5 ) kJ mol -1 ) 337.0 ( 2.5 kJ mol -1 , a result which is in agreement with the recent determinations of 339.4 ( 2.5 and 338 ( 3 kJ mol -1 .…”

Photodissociation of benzene under collision-free conditions: An ab initio/Rice–Ramsperger–Kassel–Marcus study

“…For the C 6 H 5 ϩH channel, we additionally carried out similar calculations with scaling the CCSD͑T͒/6-311G** energy to the experimental energy of these products with respect to benzene, i.e., the experimental C-H bond energy. As the C-H bond energy obtained at the G2M level, 115.2 kcal/mol, 22,39 deviates by ϳ3 kcal/mol from the experimental value of 112.0Ϯ0.6 kcal/mol, 40 this may affect the C 6 H 6 →C 6 H 5 ϩH variational rate constants, especially, at low excitation energies. Finally, the variational transition states with the minimal values of the number of states were employed to calculate rate constants of the direct dissociation processes using the above RRKM formalism.…”

“…1, the calculated C-H bond energy in C 6 H 6 ͑isomer 1͒ is 115.2 kcal/mol at the G2M level, somewhat higher than the experimental value of 112Ϯ0.6 kcal/mol. 40 The H-elimination occurs without an exit barrier. Additionally, the hydrogen loss can be preceded by migration of a hydrogen atom around the aromatic ring.…”

Determination of Bond Dissociation Enthalpies in Solution by Photoacoustic Calorimetry

“…While the bond strengths in many simple hydrocarbons have been measured using various gas phase techniques 4 to a precision of 1-2 kcal mol -1 , the accepted absolute values have changed significantly over the last 30 years. For instance, the BDE-(C-H) in benzene has risen from 103 5 to 113.5 6 kcal mol -1 and that of the benzylic C-H in toluene from 85 5 to 90 4 kcal mol -1 . Consequently, many BDEs that were derived using these reference values changed as well.…”