Understanding the isomerization kinetics in the gas phase of a triazole-3-thione derivative: A theoretical approach
The isomerization reactions of the 4-amino-5-methyl-2,4-dihydro- -3H-1,2,4-triazole-3-thione were studied using the B3LYP and M06-2x, as well as the CBS-QB3 theoretical methods. The measured energy profiles were complemented with kinetic rate constants using the transition state theory (TST). Based on the isomers geometries optimized using the CBS-QB3 method, a natural bond orbital (NBO) analysis shows that the stabilization energies of non-bonding lone-pair orbitals [LP(e)S7] to the ?*N2?C3 antibonding orbital increase from isomers 1 to 2. Moreover, the LP(e)S7 ? ?*N2?C3 delocalizations could fairly explain the increase in the occupancies of LP(e)S7 orbitals for isomers 1 and 2 (2 > 1). The studied stabilization energy increases the stability of the ground state structure, and could fairly explain the kinetics of the isomerization reactions 1 and 2 (k2 > k1). NBO results also suggest that the kinetics of these processes are controlled by the LP ??* resonance energies.