TY - JOUR
T1 - The enthalpies of formation of o-, m-, and p-benzoquinone
T2 - Gas-phase ion energetics, combustion calorimetry, and quantum chemical computations combined
AU - Fattahi, Alireza
AU - Kass, Steven R.
AU - Liebman, Joel F.
AU - Matos, M. Agostinha R
AU - Miranda, Margarida S.
AU - Morais, Victor M F
PY - 2005/4/27
Y1 - 2005/4/27
N2 - 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 (ΔhydH°(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 (ΔfH°(1o, 1m, and 1p) = -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 (ΔfH°(g) = -73.09 ± 0.87 kcal mol-1) was transformed to ΔfH°(1o) = -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 ΔfH°(1o) = -21.0 ± 3.1 kcal mol-1. Additivity was found to work well for m-benzoquinone, but BDE1 and BDE2 for 1,2- and 1,4-dihydroxybenzene differed by a remarkably small 14.1 ± 4.2 and 23.5 ± 3.7 kcal mol-1, respectively, indicating that o- and p-benzoquinone should be excellent radical traps.
AB - 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 (ΔhydH°(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 (ΔfH°(1o, 1m, and 1p) = -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 (ΔfH°(g) = -73.09 ± 0.87 kcal mol-1) was transformed to ΔfH°(1o) = -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 ΔfH°(1o) = -21.0 ± 3.1 kcal mol-1. Additivity was found to work well for m-benzoquinone, but BDE1 and BDE2 for 1,2- and 1,4-dihydroxybenzene differed by a remarkably small 14.1 ± 4.2 and 23.5 ± 3.7 kcal mol-1, respectively, indicating that o- and p-benzoquinone should be excellent radical traps.
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U2 - 10.1021/ja042612f
DO - 10.1021/ja042612f
M3 - Article
C2 - 15839713
AN - SCOPUS:17744379599
SN - 0002-7863
VL - 127
SP - 6116
EP - 6122
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 16
ER -