The chemical equilibrium of mutual interconversions of tert-amylbenzenes was studied in the temperature range 286-423 K using chloroaluminate ionic liquids as a catalyst. Enthalpies of isomerization and transalkylation of tert-amylbenzene were obtained from temperature dependences of the corresponding equilibrium constants in the liquid phase. The molar enthalpy of formation of tert-amylbenzene was measured using combustion calorimetry and was also obtained by the transpiration method. Using these experimental results, high-level ab initio methods (B3LYP and G3MP2) have been successfully tested for the prediction of reaction enthalpies for the four reactions under study. New experimental results have been used to derive a strain of tert-amylbenzene, which is useful in any additive scheme as the non-nearest-neighbor interaction which is specific for the branched alkylbenzenes.
Standard molar enthalpies of formation in the gaseous state of a series of alkyl 3-methylbut-2-enoates have been obtained from combustion calorimetry and results from the temperature dependence of the vapor pressure measured by the transpiration method. To verify the experimental data, we have performed ab initio calculations of all compounds. Enthalpies of formation derived from the G3MP2 method are in excellent agreement with the experimental results. Quantitative analysis of strain effects in alkyl 3-methylbut-2-enoates was discussed in terms of deviations of deltafH degrees m(g) from the group additivity rules. Energetics of the cis-trans isomerization of carboxylic acid derivatives was studied using G3MP2 and DFT methods. Values of strain and cis-trans corrections derived in this work provide further improvement on the group-contribution methodology for prediction of the thermodynamic properties of compounds relevant to biodiesel.
This work has been undertaken to obtain new thermochemical data for ethanediol and propanetriol acetates and to improve the group contribution methodology for the prediction of the thermodynamic properties of compounds relevant to biodiesel. Standard molar enthalpies of formation in the gaseous state of a series of 1,2-ethanediol monoacetate, 1,2-ethanediol diacetate, and 1,2,3-propanetriol triacetate have been obtained from combustion calorimetry and results from the temperature dependence of the vapor pressure measured by the transpiration method. To verify the experimental data, ab initio calculations of all compounds have been performed. Enthalpies of formation derived from the Gaussian 03 second-order Møller−Plesset (G3MP2) method are in good agreement with the experimental results. The strength of the hydrogen bond in 1,2-ethanediol monoacetate and in 1,2-ethanediol have been obtained using ab initio calculations and the group additivity method.
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