Experimental enthalpies of formation and sublimation of urea compounds: An accuracy assessment.

Graphical abstract Highlights • Thermochemical network of isodesmic reactions is applied to urea and its derivatives. • 8 ureas are recommended as reference species. • Experimental enthalpies of formation for 9 ureas require reexamination. Abstract The thermochemical network of 91 isodesmic and other balanced reactions was used to adjust simultaneously the enthalpies of formation of 14 urea compounds. The experimental enthalpies of formation of these compounds were treated as unknowns in the least-squares minimization of deviations between the theoretically predicted enthalpies of reaction and experimental values. A result of a least-squares fit confirms the accuracy of experimental enthalpies of formation of 8 ureas, whereas the experimental measurements for 6 urea compounds require re-examination. The gas-phase standard enthalpies of formation of 8 ureas were used as a consistent basis to obtain values for other 15 ureas through isodesmic reactions. To estimate the enthalpies of formation in crystalline state, the sublimation enthalpies were predicted using the molecular electrostatic potential model. [ABSTRACT FROM AUTHOR]