The spin-delocalization substituent parameter σjj. Part 10. The spin-delocalizing abilities of the para-trifluorovinyl and para-acetoxy groups. synthesis of para-trifluorovinyl-, para-vinyland para-acetoxy-α,β,β-trifluorostyrenes

Abstract para -Trifluorovinyl α,β,β -trifluorostyrene ( 1-CF=CF 2 ), p -acetoxy α,β,β -trifluorostyrene ( 1-AcO ) and p -vinyl α,β,β -trifluorostyrene ( 1-CH=CH 2 ) have been synthesized. The rate constants ( k ) for the thermal cyclodimerization of 1-CF=CF 2 and 1-AcO have been measured over the temperature range 90–130 °C for 1-CF=CF 2 and 110–160 °C for 1-AcO . The σ mb polar substituent constants of the p -CF=CF 2 , p CH=CH 2 and p -AcO groups calculated from the 19 F NMR chemical shifts are: for p -CF=CF 2 , 0.40; for p -CH=CH 2 , 0.03; and for p -AcO, −0.14, and the σ JJ spin-delocalization substituent constants of the p -CF=CF 2 and b 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=CH 2 group could not be accurately measured, but it was very roughly estimated to be in the range of 0.50–0.66.