The spin-delocalization substituent parameter σ JJ?. Part 10. The spin-delocalizing abilities of the para-trifluorovinyl and para-acetoxy groups. Synthesis of para-trifluorovinyl-, para-vinyl-and para-acetoxy-α,β,β-trifluorostyrenes

Article abstract of DOI:10.1016/S0022-1139(96)03487-2

para-Trifluorovinyl α,β,β-trifluorostyrene (1-CF=CF₂), p-acetoxy α,β,β-trifluorostyrene (1-AcO) and p-vinyl α,β,β-trifluorostyrene (1-CH=CH₂) have been synthesized. The rate constants (k) for the thermal cyclodimerization of 1-CF=CF₂ and 1-AcO have been measured over the temperature range 90-130 °C for 1-CF=CF₂ and 110-160 °C for 1-AcO. The σ_mb polar substituent constants of the p-CF=CF₂, p-CH=CH₂ and p-AcO groups calculated from the ¹⁹F NMR chemical shifts are: for p-CF=CF₂, 0.40; for p-CH=CH₂, 0.03; and for p-AcO, -0.14, and the σ _JJ^? spin-delocalization substituent constants of the p-CF=CF₂ and p-AcO groups are 0.86 and 0.35, respectively, i.e., the former is a highly effective spin-stabilizer while the latter is moderately effective. Owing to the occurrence of a small amount of side-reaction, the σ _JJ^? value of the p-CH=CH₂ group could not be accurately measured, but it was very roughly estimated to be in the range of 0.50-0.66.