Theoretical study on the mechanism of the reaction: HCCCH2 ++C2H2→c-C3H3 ++C2H2

The gas phase ion–molecule reaction of propargylium (HCCCH2 +) with acetylene (C2H2) to produce cyclopropenylium (c-C3H3 +) with C2H2 has been investigated theoretically at the B3LYP/6–31G(d) and single-point QCISD/6–311G(d,p) levels. The detailed mechanism for the observed isotope exchange between HCCCH2 + and C2D2 has also discussed. Three intermediates 1 CH2CCH2CCH+, 2 H2C2·CHCCH2 + and 3 c-C4H3–CH2 + are shown to play important roles in the product formation and isotope exchange processes, rather than the low-lying isomers 4 c-C3H2–CH2 +, 7 c-(CH)5 + and 8 pyramidal C5H5 +. Our calculated results agree well with the available experimental data and may be helpful for understanding the mechanism for combustion processes.