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

A detailed doublet potential energy surface for the reaction of CH with CH3CCH 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 CH3CCH, forming CH3CCHCH 1 (1a,1b). Starting from 1 (1a,1b), the most feasible pathway is the ring closure of 1a to CH3–cCCHCH 2 followed by dissociation to P3(CH3–cCCCH+H), or a 2,3 H shift in 1a to form CH3CHCCH 3 followed by C–H bond cleavage to form P5(CH2CHCCH+H), or a 1,2 H-shift in 1 (1a, 1b) to form CH3CCCH24 followed by C–H bond fission to form P6(CH2CCCH2+H). Much less competitively, 1 (1a,1b) can undergo 3,4 H shift to form CH2CHCHCH 5. Subsequently, 5 can undergo either C–H bond cleavage to form P5 (CH2CHCCH+H) or C–C bond cleavage to generate P7 (C2H2+C2H3). Our calculated results may represent the first mechanistic study of the CH + CH3CCH reaction, and may thus lead to a deeper understanding of the title reaction.