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

The reactions of azido-cyclization in 3,6-di(azido)-1,2,4,5-tetrazine were studied by B3LYP hybrid density functional method. The geometries of the reactants, transition states and products were optimized, and the conformation of the initial reactant was determined by IR spectra. In addition, the nucleus-independent chemical shift (NICS) indices were used to discuss the aromaticity of the products. Moreover, solvent effects were investigated. Results show that the polar solvent DMSO can hardly influence the activation barriers of all the reaction paths; however, it can stabilize the products. Since the activation barriers of azido-rotation are far less than that of the rate-determining step (the cyclization of second azido), the products are most probably the mixtures of two isomers (DAT2c and DAT2c').