Theoretical Study on the Azido-cyclization of 3,6-Di(azido)-1,2,4,5-tetrazine

Theoretical Studies on the Mechanism of the Azido-Tetrazole of Azido-s-triazine

The B3LYP/aug-cc-pvDZ level of theory has been applied to the study of the molecular structures, electronic structures and the azido-tetrazole isomerization of 1-azido-s-triazine, 1,3-diazido-s-triazine and 1,3,5-triazido-s-triazine. NBO analysis was applied to investigate the atomic natural charge and stabilization interaction energies among molecules. The results showed that the reaction initially proceeds through the loss of the linearity of the azido group and the approaching of the terminal nitrogen atom of the azide group to the nitrogen atom of the ring. This is followed by an attack of the lone pairs on N atoms in the ring to the azido group, leading to the formation of the N-N bonds. Many factors, including bending of the bond angle, electrostatic attraction, orbital delocalization and the stabilization interaction give rise to a large free energy barrier for the cyclization process. The results also show that the second and third cyclization is relatively easier than the first one.