Isomerization reaction and kinetics of dihydro-tetrazine

The mechanism of hydrogen transfer isomerization reactions for dihydro-tetrazine is studied by Gaussian03 program. The optimized structures and the frequencies of all the stationary points are calculated at the B3LYP/6-311 + +G** level. The minimum-energy paths are obtained by using the intrinsic reaction coordinate (IRC) theory. The reaction potential energy curve is obtained by CCSD (T)/6-311 + + G** level. The rate constants are evaluated over a wide temperature region from 200 to 2 500 K using TST, TST/Eckart, CVT, CVT/ SCT, and CVT/ZCT theories. Analysis of the energetic parameters indicates that the reaction is an endothermic and unspontaneous process at the room temperature. The obtained results indicate that the variational effects are small over the whole temperature range, while the tunneling effects are remarkable at low temperature (200K<T <500K).