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Accurate Prediction of Enthalpies of Formation of Organic Azides by Combining G4 Theory Calculations with an Isodesmic Reaction Scheme
journal contribution
posted on 2013-08-08, 00:00 authored by Olga V. Dorofeeva, Oxana N. Ryzhova, Marina A. SuntsovaAccurate
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.