The enthalpies of formation of o-, m-, and p-benzoquinone: Gas-phase ion energetics, combustion calorimetry, and quantum chemical computations combined

• Tipo: Artigo em Revista Científica Internacional
• Data: 2005

Autores

Fattahi, A (Autor) Outra; Kass, SR (Autor) Outra; Liebman, JF (Autor) Outra; Matos, MAR (Autor) FCUP; Miranda, MS (Autor) Outra; Morais, VMF (Autor) ICBAS

Revista

Título: Journal of the American Chemical Society

Vol. 127 Nº 41

Páginas: 6116-6122

ISSN: 0002-7863

Editora: American Chemical Society

Indexação

ISI Web of Knowledge - 45 Citações

Scopus - 44 Citações

Classificação Científica

FOS: Ciências exactas e naturais > Química

Outras Informações

ID Authenticus: P-000-3SQ

DOI: 10.1021/ja042612f

Abstract (EN): 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(t)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) = -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.

Idioma: Inglês

Tipo (Avaliação Docente): Científica

Nº de páginas: 7