Thermodynamic properties of 2,7-di-tert-butylfluorene - An experimental and computational study

This work presents a comprehensive experimental and computational study of the thermodynamic properties of 2,7-di-tert-butylfluorene. The standard (p(o) = 0.1 MPa) molar enthalpy of formation in the crystalline phase was derived from the standard molar energy of combustion, measured by static bomb combustion calorimetry. The enthalpies and temperatures of transition between condensed phases were determined from DSC experiments. The vapour pressures of the crystalline and liquid phases were measured between (349.14 and 404.04) K, using two different experimental methods. From these results the standard molar enthalpies, entropies and Gibbs energies of sublimation and of vaporization were derived. The enthalpy of sublimation was also determined using Calvet microcalorimetry. The thermodynamic stability of 2,7-di-tert-butylfluorene in the crystalline and gaseous phases was evaluated by the determination of the standard Gibbs energies of formation, at the temperature 298.15 K, and compared with the ones reported in the literature for fluorene. A computational study at the G3(MP2)//B3LYP and G3 levels has been carried out. A conformational analysis has been performed and the enthalpy of formation of 2,7-di-tert-butylfluorene has been calculated, using atomization and isodesmic reactions. The calculated enthalpies of formation have been compared to the experimental values. (C) 2016 Elsevier Ltd.