1. The Enthalpies of Formation of o-, m-, and p-Benzoquinone: Gas-Phase Ion Energetics, Combustion Calorimetry, and Quantum Chemical Computations Combined.
- Author
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Fattahi, Alireza, Kass, Steven R., Liebman, Joel F., Matos, M. Agostinha R., Miranda, Margarida S., and Morais, Victor M. F.
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ENTHALPY , *ANIONS , *COMBUSTION , *CALORIMETRY , *TEMPERATURE measurements , *CHEMISTRY - Abstract
Radical anions of O-, m-, and p-benzoquinone were produced in a Fourier transform mass spectrometer by low energy electron attachment or collision-induced dissociation and were differentiated. Classical derivatization experiments also were carried out to authenticate the ortho and meta anions. Gas- phase techniques were used to measure the proton affinities of all three radical anions and the electron affinities of o- and m-benzoquinone. By combining these results in thermodynamic cycles, we derived heats of hydrogenation of o-, m-, and p-benzoquinone (AhydHo(1O, 1m, and 1p) = 42.8 ± 4.1, 74.8 ± 4.1, and 38.5 ± 3.0 kcal mol-1, respectively) and their heats of formation (Ad-P(1o, 1 m, and Ip) = -23.1 ± 4.1, 6.8 ± 4.1, and -27.7 ± 3.0 kcal mol-1, respectively). Good accord with the literature value for the para derivative was obtained. Combustion calorimetry and heats of sublimation also were measured for benzil and 3,5- di-tert-butyl-o-benzoquinone. The former heat of formation agreed with previous determinations, while the latter result (AfI-f(g) = -73.09 ± 0.87 kcal mol-1) was transformed to A1H°(lo) = -18.9 ± 2.2 kcal mol-1 by removing the effect of the tert-butyl groups via isodesmic reactions. This led to a final value of AH°(10) = -21.0 ± 3.1 kcal mol-1. Additivity was found to work well for m-benzoquinone, but BDE1 and BDE2 for 1,2- and I ,4-dihydroxybenzene differed by a remarkably small 14.1 ± 4.2 and 23.5 ± 3.7 kcal mol1, respectively, indicating that o- and p-benzoquinone should be excellent radical traps. [ABSTRACT FROM AUTHOR]
- Published
- 2005
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