Abstract: Density functional(B3LYP) calculations, using the 6-31G* and LANL2DZdp ECP Polarization basis sets, were employed to study the reaction pathway involving 3-methylthio-4-cyano-pyrazole and iodomethane. According to the structure of pyrazole derivatives, two possible reaction pathways were examined. Pathway Ⅰ proceeded associated with the dehydrogenation of the reactants and the attack of CH₃I on both nitrogen atoms of pyrazole. Pathway Ⅱ was as follows: first, due to the hydrogen transfer of the reactants, two isomers are formed; then CH₃I attacks on nitrogen atom of the isomers to form intermediates; finally the intermediates dehydroiodinate to form two products. The results from the calculation suggest that pathway Ⅱ is the dominant reaction channel.

Key words: Density functional theory, Transition state, Pyrazole derivatives, Reaction pathway