Theoretical mechanistic study of the reaction of the methylidyne radical with methylacetylene.

A detailed doublet potential energy surface for the reaction of CH with CH(3)CCH is investigated at the B3LYP/6-311G(d,p) and G3B3 (single-point) levels. Various possible reaction pathways are probed. It is shown that the reaction is initiated by the addition of CH to the terminal C atom of CH(3)CCH, forming CH(3)CCHCH 1 (1a,1b). Starting from 1 (1a,1b), the most feasible pathway is the ring closure of 1a to CH(3)-cCCHCH 2 followed by dissociation to P ( 3 )(CH(3)-cCCCH+H), or a 2,3 H shift in 1a to form CH(3)CHCCH 3 followed by C-H bond cleavage to form P ( 5 )(CH(2)CHCCH+H), or a 1,2 H-shift in 1 (1a, 1b) to form CH(3)CCCH(2) 4 followed by C-H bond fission to form P ( 6 )(CH(2)CCCH(2)+H). Much less competitively, 1 (1a,1b) can undergo 3,4 H shift to form CH(2)CHCHCH 5. Subsequently, 5 can undergo either C-H bond cleavage to form P ( 5 ) (CH(2)CHCCH+H) or C-C bond cleavage to generate P ( 7 ) (C(2)H(2)+C(2)H(3)). Our calculated results may represent the first mechanistic study of the CH + CH(3)CCH reaction, and may thus lead to a deeper understanding of the title reaction.