C-H bond energy of benzene

Journal Article · Wed Mar 08 04:00:00 EST 1995 · Journal of the American Chemical Society; (United States)

DOI:https://doi.org/10.1021/ja00114a023· OSTI ID:6563807

Davico, G E; Bierbaum, V M; DePuy, C H; Ellison, G B ^[1]; Squires, R R ^[2]

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1. Univ. of Colorado, Boulder, CO (United States)
2. Purdue Univ., West Lafayette, IN (United States)

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 for 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.

• DOE Contract Number: FG02-87ER13695
• OSTI ID: 6563807
• Journal Information: Journal of the American Chemical Society; (United States), Journal Name: Journal of the American Chemical Society; (United States) Vol. 117:9; ISSN JACSAT; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400102 -- Chemical & Spectral Procedures
400201* -- Chemical & Physicochemical Properties
99 GENERAL AND MISCELLANEOUS
990200 -- Mathematics & Computers
AFFINITY
AMIDES
AMMONIA
AROMATICS
ARYL RADICALS
BENZENE
CHARGED PARTICLES
CHEMICAL BONDS
CHEMICAL REACTION KINETICS
DATA
DISSOCIATION HEAT
ELECTRON SPECTROSCOPY
ENTHALPY
FORMATION HEAT
HYDRIDES
HYDROCARBONS
HYDROGEN COMPOUNDS
INFORMATION
IONIZATION
IONS
KINETICS
MASS SPECTROSCOPY
MATHEMATICAL MODELS
MOLECULAR MODELS
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHENYL RADICALS
PHOTOELECTRON SPECTROSCOPY
PHOTOIONIZATION
PHYSICAL PROPERTIES
RADICALS
REACTION HEAT
REACTION KINETICS
SPECTROSCOPY
THERMODYNAMIC PROPERTIES