ABSTRACT

The synergetic use of bonding evolution theory (BET) and noncovalent interaction (NCI) analysis allows to obtain new insight into the bond breaking/forming processes and electron redistribution along the reaction path to understand the molecular mechanism of a reaction and recognize regions of strong and weak electron pairing. This viewpoint has been considered for cheletropic extrusion of CO from unsaturated cyclic ketones cyclohepta-3,5-dien-1-one CHD, cyclopent−3-en-1-one CPE, and bicyclo[2.2.1]hept-2-en-7-one BCH by using hybrid functional MPWB1K in conjugation with aug-cc-pVTZ basis set. Decarbonylation of CHD, CPE, and BCH are nonpolar cyclo-elimination reactions that are characterized by the sequence of turning points (TPs) as CHD, 1−11-C[CC]C† C† FFFTSC† C† C† −0:HT + CO; CPE, 1−8-CC[C† C† F† ]- [FF][FF]FTS[C† C† ]−0:BD + CO; and BCH, 1−8-CC[C† C† ]F[FF]FTS[C† C† ]− 0:CD + CO. Breaking of C−C bond between the terminal carbon atoms of diene/ triene framework and carbon atom of CO fragment starts at a distance of ca. 1.9− 2.0 Å in the vicinity of the transition structure where the transition states are not reached yet. NCI analysis explains that the noncovalent interactions between two fragments appeared after the breaking of C−C bonds.