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Four substituted α,β,β-trifluorostyrenes (TFSs) namely,p-trimethylsilyltrifluoro-styrene (1),p-acetyltrifluorostyrene ethylene ketal (2),p-acetyltrifluorostyrene (3) and p-pnenoxy-trifluorostyrene (4),have been synthesized.The rate constants (k_2) of the thermal cyclodimer-ization of 1 and 3 have been measured in the temperature range 120—160℃.The polar para-meters _σp of the four TFSs calculated from ~(19)F NMR chemical shifts are:for p-trimethylsilyl-1,0.21;1-ethylenedioxy-ethyl-,—0.01;p-acetyl-,0.61 and p-phenoxy-,—0.47.The spin de-localization substituent parameters σ·T of p-trimethylsilyl and p-acetyl groups are 0.29 and 0.52respectively.Thus both the p-trimethylsilyl and the p-acetyl groups act as electron-attractinggroups which can also effectively stabilize a spin.
P-trimethylsilyltrifluoro-styrene (1), p-acetyltrifluorostyrene ethylene ketal (2), p-acetyltrifluorostyrene (3) and p-pnenoxy-trifluorostyrene synthesized. The constants (k_2) of the thermal cyclodimer-ization of 1 and 3 have been measured in the temperature range 120-160 ° C. The polar para-meters _σp of the four TFSs calculated from ~ (19) F NMR chemical shifts are: p-trimethylsilyl-1, 0.21; 1-ethylenedioxy-ethyl-, -0.01; p-acetyl-, 0.61 and p-phenoxy-, and p-acetyl groups are 0.29 and 0.52respectively.Thus both the p-trimethylsilyl and the p-acetyl groups act as electron-attracting groups which can also be effectively stabilized a spin.