“…We have investigated the formation and cyclization of nitrile imine 3 at the M06/6-311 + G(d,p) level of theory (Figure ). The N 2 -elimination from tetrazoles can be described as concerted, one-step reactions. ,, Valence tautomeric diazo compound 2 is found to be an energy minimum in the decomposition of 2-phenyl-5-styryltetrazole 1 , but the concerted N 2 loss (TS3) has a lower overall activation energy (see Scheme and Figures , , and S1 (Supporting Information)). The free energy of activation of 36.4 kcal/mol is in line with the experimental activation energies for several 2,5-disubstituted tetrazoles (34–43 kcal/mol) .…”