Quantum Chemistry Study on the Cycloaddition Reaction of Difluorocarbene and Formaldehyde

The mechanism of the cycloaddition reaction of singlet difluorocarbene with formaldehydehas been studied by RHF/6-31G^* gradient method. The electron correlation energies of all the structures are calculated by using second-order Moller-Plesset perturbation theory （MP2）. We have also calculated the changes of thermdynamic functions and the quality of kinetic properties for this reaction at different temperatures by using statistical thermodynamics method and transition-state theory. The results show that this reaction proceeds in two steps: （1） difluorocarbene and formaldehyde form an intermediate complex,which is a kind of exothermal reaction with no barrier; （2） the intermediate complex isomerized to the product, after being corrected by zero-point energies, the barrier is 124.90kJ/mol （MP2/6-31G^*/6-31G^*）. In view of dynamics and thermodynamics,it is between 500～800K that the reaction will have not only the larger spontaneous tendency and equilibrum constant but also quicker reaction rate.