Enthalpies of formation of diamantanes in the gas and crystalline phase: comparison of theory and experiment

Abstract

Gas-phase enthalpies of formation of diamantane and some of its derivatives were calculated from isodesmic reactions using adamantane as reference species. The G4 theory was applied to calculate the energies of all molecules involved in the isodesmic reactions. The sublimation enthalpies were predicted by the molecular electrostatic potential (MEP) model. Their values were computed from an equation that describes the relationship between the sublimation enthalpy and computed crystal density, and molecular surface area plus four quantities obtained from the surface electrostatic potential. The coefficients in this equation were determined earlier from least squares fitting to reliable values of sublimation enthalpy of 23 adamantanes. The enthalpy formation of diamantanes in the crystalline phase was estimated on the basis of calculated gas-phase enthalpies of formation and sublimation enthalpies. The difference between experimental and theoretical data and inconsistencies in available experimental data are discussed.