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 (Δ<sub>f</sub><i>H</i><sub>298</sub><sup>°</sup>) of 29 azides are recommended by combining G4 theory calculations with an isodesmic reaction approach. The internal consistency over a set of Δ<sub>f</sub><i>H</i><sub>298</sub><sup>°</sup> values was achieved by sequential adjustment of their values through the isodesmic reactions. The HN<sub>3</sub> 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.