Aromaticity of azines through dyotropic double hydrogen transfer reaction.

Density functional theory calculations have been performed at B3LYP/6-31+G (d) level to quantify the aromaticities of mono- to triazines through dyotropic double hydrogen transfer (DDHT) reaction. The reaction was chosen such that the azines are products of double hydrogen dyotropic rearrangement, and activation barriers and energies of the reactions were functions of the aromaticities of azines. Small activation barriers and high energies of reactions were characteristic of the reactions delivering highly aromatic azines. Synchronicity, reaction energies and energies of activation have been analyzed, and the aromaticity values obtained thereof were compared with the aromaticity values from other geometric and magnetic criteria. Energies of activation were found superior to the energies of reaction for the determination of the aromaticities. Aromaticities of most of the azines were comparable to the aromaticity of benzene. Activation barriers and reaction energies for the dyotropic reactions delivering contiguous or polynitrogeneous azines had thermodynamic contributions arising from the contiguous nature of azines, in addition to the aromaticity related thermodynamic contributions. Moreover, the aromaticity values of azines are also affected by the fusion of azine to the reaction center. When corrected for these factors, the aromaticities of azines using energies of activation for DDHT correlated nicely with the aromaticities of azines reported in the literature through NICS(0)πzz and some other energetic methods.