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| - Enthalpy of Sublimation in the Study of the Solid State of Organic Compounds. Applicationto Erythritol and Threitol
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| - The enthalpies of sublimation of erythritol and l-threitol have been determined at 298.15 K by calorimetry.The values obtained for the two diastereomers differ from one another by 17 kJ mol-1. An interpretation ofthese results is based on the decomposition of this thermodynamic property in a term coming from theintermolecular interactions of the molecules in the crystal (ΔintH°) and another one related with theconformational change of the molecules on going from the crystal lattice to the most stable forms in the gasphase (ΔconfH°). This last term was calculated from the values of the enthalpy of the molecules in the gasstate and of the enthalpy of the isolated molecules with the crystal conformation. Both quantities were obtainedby density functional theory (DFT) calculations at the B3LYP/6-311G++(d,p) level of theory. The resultsobtained in this study show that the most important contribution to the differences observed in the enthalpyof sublimation are the differences in the enthalpy of conformational change (13 kJ mol-1) rather than differentintermolecular forces exhibited in the solid phase. This is explained by the lower enthalpy of threitol in thegas phase relative to erythritol, which is attributed to the higher strength of the intramolecular hydrogenbonds in the former. The comparison of the calculated infrared spectra obtained for the two compounds inthe gas phase supports this interpretation.
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