An ab initio study of potential energy surfaces of CH3COCN dissociation on the low-lying states

The C-CH, and C-CN bond dissociations of CH3COCN on S-1 and T-1 surfaces are studied at the CAS(8,7)/cc-pVDZ level. The results show that the intersystem crossing from S-1 to T-1 is a favorable pathway of S, deactivation. Once on the T-1 surface, the system can dissociate adiabatically to CH3 ((X) over tilde) + OCCN ((X) over tilde) or CN ((X) over tilde) + CH3CO ((X) over tilde), but the former has some preference over the latter. This mechanism is consistent with Cheng's presumption deduced from the experimental facts and theoretical considerations. A comparison with other asymmetrically substituted carbonyl compounds suggests that the selectivity of the alpha-bond cleavage is mainly dependent on the mechanism of dissociation. (C) 2002 Elsevier Science B.V. All rights reserved.