A THEORETICAL-STUDY OF THE HCHO- CYCLOADDITION OR YLIDE FORMATION(CCL2 REACTION )

The chemical reaction between HCHO and CCl2 was studied using a high l evel of theory. Geometry optimizations were performed at the complete active space self-consistent field (CASSCF) level with the 6-31G basi s set, and single point calculations were performed using the coupled- cluster with single, double, and perturbative inclusion of triple exci tation [CCSD(T)] method. Additivity approximation of the correlation e nergy was used, so we have obtained an effective CCSD(T)/6-311G(2d1f,2 p) reaction and activation energies. Our results show that the ylide e xist as astable species, having a transient character. Its lifetime in relation to ring closure was estimated to be 1 ms at 298.15 K, and it can react backward forming the HCHO and CCl2, fragments. The cycloadd ition reaction is highly competitive with ylide formation, and that is the dominant process. The reaction rate of cycloaddition is about two and a half times higher than the ylide formation at 298.15 K. (C) 199 7 American Institute of Physics.