Accurate Prediction of Enthalpies of Formation of Organic Azides by Combining G4 Theory Calculations with an Isodesmic Reaction Scheme
journal contributionposted on 08.08.2013 by Olga V. Dorofeeva, Oxana N. Ryzhova, Marina A. Suntsova
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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.