2π + 2π cycloaddition kinetics of some fluoro olefins and fluoro vinyl ethers

The second order 2π + 2π homo- and co-dimerization between various classes of fluorinated olefins has been investigated. The fluorinated olefins examined in this study were: (1) RfOCFCF2 (perfluorinated vinyl ethers); (2) RfCFCF2 (perfluorinated terminal olefins); (3) RCH2CFCF2; (4) PhOCFCF2 (aryl perfluorinated vinyl ethers). imerizations between vinyl ethers have an Ea between 20 and 24 kcal mol−1 while homo-dimerizations between terminal olefins have an average Ea between 35 and 40 kcal mol−1; vinyl groups have a second order cyclodimerization rate constant of formation between 1 × 10−7 and 1 × 10−4 M−1 S−1 while vinyl ethers have a second order cyclodimerization rate constant of formation = 1 × 10−1 M−1 s−1. If there is a CH2 group α to the terminal olefin, the Ea of cyclodimerization is about 7 kcal mol−1) lower with respect to those olefins with a CF2 α to the instauration. At 270 °C co-dimerizations have an average ΔS≠ = −45 cal K−1 mol−1 and a second order rate constant of cyclodimerization ranging between 0.1 × 10−4 M−1 S−1 and 16 × 10−4 M−1 S−1 while homo-dimerizations have an average ΔS≠ = −17 cal K−1 mol−1 and a second order rate constant which can span from 7 × 10−7 M−1 S−1 to as much as 1 × 10−1 M−1 S−1 depending on the electronic nature of the perfluorinated terminal olefin. correlation between the electronegativity χ and the activation energy Ea demonstrates that “polarizing” groups, O, PhO, α to the olefin play an important role in the formation and stabilization of the cyclodimerization biradical intermediate.