Enthalpy of formation of guanidine and its amino and nitro derivatives.

The gas-phase enthalpies of formation ( $${\Delta_{\text{f}}}H_{ 2 9 8}^\circ$$ ) of guanidine and its 10 amino and nitro derivatives were calculated using the isodesmic reaction method at the Gaussian-4 level of theory. The enthalpies of sublimation ( $${\Delta_{\text{sub}}}H_{ 2 9 8}^\circ$$ ) were estimated in the framework of the Politzer approach that combines the empirical equation for enthalpy of sublimation with the B3LYP/cc-pVTZ calculations of the electronic properties of the molecular surfaces. The enthalpies of sublimation of mono-, di-, and triaminoguanidine were also estimated using experimental data for their salts. On the basis of the calculated $${\Delta_{\text{f}}}H_{ 2 9 8}^\circ$$ (g) and $${\Delta_{\text{sub}}}H_{ 2 9 8}^\circ$$ values, the solid-phase enthalpies of formation were estimated for all guanidine derivatives. A predictive model confirms the available experimental data for guanidine, nitroguanidine, and some of their derivatives. The calculated value of solid-phase enthalpy of formation of high-nitrogen energetic compound 3,6-bis(2-nitroguanidino)-1,2,4,5-tetrazine is also in reasonable agreement with the reported experimental values. [ABSTRACT FROM AUTHOR]