The Enthalpies of Formation of o-, m-, and p-Benzoquinone:  Gas-Phase Ion Energetics, Combustion Calorimetry, and Quantum Chemical Computations Combined

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 (Delta(hyd)H degrees (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 (Delta(f)H degrees (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 (Delta(f)H degrees (g) = -73.09 +/- 0.87 kcal mol(-)(1)) was transformed to Delta(f)H degrees (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 Delta(f)H degrees (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.

Interplay of Thermochemistry and Structural Chemistry, the Journal (Volume 14, 2003) and the Discipline

“…The cage studied in the current paper is 4-oxa-hexacyclo [5.4.1.0 2,6 .0 3,10 .0 8,22 ] dodecane and extends their earlier studies involving other oxygenated polycyclic cage species. None of these oxygenated cage species' enthalpies of formation are known.…”

“…These quinones may be recognized as o-benzoquinones for which one may ask how much less stable are these than their isomeric p-isomers: after all, numerous p-benzoquinones are readily isolable while few o-benzoquinones so survive. In a recent study, the sole experimental investigation on the thermochemistry of o-benzoquinones shows the parent compound is only some 20 kJ/mol less stable than the well-known and much more kinetically stable p-isomer [22]. This difference is surprisingly small.…”

Paradigms and paradoxes: Energetics of the oxidative cleavage of indigo and of other olefins

“…f We averaged the archival enthalpy of formation of gas-phase glyoxal with the new value for its diphenylated derivative (benzil) from Ref. [26]. g We approximated the enthalpy of sublimation of this species by the archival value (Ref.…”

Benzoylnitrene radical anion: A new reagent for the generation of M-2H anions

“…M-2H ions are also observed in reactions of 1 Ϫ with hydroquinones. Thus, reaction of m-hydroquinone gives the m-quinone radical anion (eq 3) [17]. Although dehydrophenol anions could possibly be formed by deprotonation of ring protons, they can be ruled out by the fact that M-2H anions are not formed in the reaction with phenol.…”