Accurate prediction of enthalpies of formation of organic azides by combining G4 theory calculations with an isodesmic reaction scheme.

Accurate gas-phase enthalpies of formation (ΔfH298°) of 29 azides are recommended by combining G4 theory calculations with an isodesmic reaction approach. The internal consistency over a set of ΔfH298° values was achieved by sequential adjustment of their values through the isodesmic reactions. The HN₃ was chosen as a key reference compound. Of the experimental data available for 16 compounds, our predictive values agree well with 9 of them, while the deviations from 25 to 55 kJ/mol are observed for 7 compounds; possible systematic errors in the experimental data for phenyl azide, 2-azidoethanol, azidocyclopentane, azidocyclohexane, 3-azido-3-ethylpentane, 2-azido-2-phenylpropane, and 1-azidoadamantane are discussed. The recommended enthalpies of formation of organic azides were used as reference values to estimate the enthalpy of formation of four nitrogen-rich carbon nitrides. The calculations do not support the high value of the solid-state enthalpy of formation of TAAT (4,4',6,6'-tetra(azido)azo-1,3,5-triazine); its value is estimated to be 300-400 kJ/mol lower than that measured experimentally.