76356-94-0Relevant academic research and scientific papers
Is benzene oxide homoaromatic? A microcalorimetric study
Jia,Brandt,Thibblin
, p. 10147 - 10152 (2001)
Rate constants and heats of reaction for the aromatization of benzene oxide (1) and the acid-catalyzed aromatization of benzene hydrate (2) in highly aqueous solution giving phenol and benzene, respectively, have been measured by heat-flow microcalorimetry. The measured heat of reaction of benzene oxide, ΔH = -57.0 kcal mol-1, is much larger than that of benzene hydrate, ΔH = -38.7 kcal mol-1, despite an unusually low reactivity of benzene oxide, rate ratio 0.08. The measured enthalpies agree with those calculated using the B3LYP hybrid functional corrected with solvation energies derived from semiempirical AM1/SM2 calculations. Comparison with the measured enthalpies of the corresponding reactions of the structurally related 1,3-cyclohexadiene oxide (3) and 2-cyclohexenol (4) of ΔH = -24.9 kcal mol-1 (includes a small calculated correction of - 1.2 kcal mol-1) and ΔH ～ 0 kcal mol-1, respectively, gives a smaller aromatization energy for the benzene oxide than for the benzene hydrate reaction (ΔΔΔH = 6.6 kcal mol-l). This suggests that benzene oxide is unusually stabilized by a significant amount of homoaromatization as has been proposed previously (J. Am. Chem. Soc. 1993, 115, 5458). This unusual stability accounts for more than half of the ～107 times lower than expected reactivity of benzene oxide toward acid-catalyzed isomerization. The rest is suggested to originate from an unusually high energy of the carbocation-forming transition state.
Kinetic and thermodynamic stability of naphthalene oxide and related compounds. A comparative microcalorimetric and computational (DFT) study
Brandt, Peter,Jia, Zhi Sheng,Thibblin, Alf
, p. 7676 - 7682 (2007/10/03)
The kinetics of the acid-catalyzed ring opening of naphthalene 1,2-oxide (5) in highly aqueous media to give naphthols has been measured by heat-flow microcalorimetry. The reaction enthalpy of this aromatization reaction was measured as ΔH = -51.3 ± 1.7 kcal mol-1. The unexpectedly low reactivity of naphthalene oxide is suggested to be due to an unusually large thermodynamic stability. A crude estimate of the stabilization effect, ～1 kcal mol-1(not a significant stabilization), is obtained by using the measured reaction enthalpies of structurally related substrates as references. A larger value (2.7 kcal mol-1) was obtained by calculation using the B3LYP hybrid functional corrected with solvation energies derived from semiempirical AM1/SM2 calculations. The origin of this effect is discussed in terms of homoconjugative stabilization and homoaromaticity. There is a good linear correlation (with slope = 0.63) between the experimentally measured free energy of activation and the calculated enthalpy of carbocation formation in water.
