The ozone–acetylene reaction: concerted or non-concerted reaction mechanism? A quantum chemical investigation

The ozone–acetylene reaction is found to proceed via an intermediate van der Waals complex (rather than a biradical), which is the precursor for a concerted symmetry-allowed [4+2] cycloaddition reaction leading to 1,2,3-trioxolene. CCSD(T)/6-311G+(2d, 2p) and CCSD(T)/CBS (complete basis set) calculations predict the ozone–acetylene van der Waals complex to be stable by 2.2 kcal mol−1, the calculated activation enthalpy for the cycloaddition reaction is 9.6 kcal mol−1 and the reaction enthalpy −55.5 kcal mol−1. Calculated kinetic data for the overall reaction (k=0.8 l mol−1 s−1, A=1.71×106 l mol−1 s−1, Ea=8.6 kcal mol−1) suggest that there is a need for refined kinetic measurements.