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Three substituted α,β,β-trifluorostyrenes(TFS’s),i.e.,p-thiomethyltrifluorostyrene(4),p-cyclopropyltrifluorostyrene(5)and p-t-butyltrifluorostyrene(6),have been synthesized.The rateconstants(k_2)of the thermal cyclodimerization of these compounds have been measured in the tem-perature range 120—160℃.The polar parameters σ_(mb) of these TFS’s calculated from ~(19)F NMR chemi-cal shifts are:for p-thiomethyl,-0.18;p-cyclopropyl,-0.31 and p-t-butyl,-0.22.The spin delo-calization substituent parameters σ’_T(140°)of p-thiomethyl,cyclopropyl and t-butyl groups are 0.59,0.27 and 0.30 respectively.Thus all of these groups act as electron-donating groups which can alsoeffectively stabilize a spin.
Three substituted α, β, β-trifluorostyrenes (TFS’s), ie, p-thiomethyltrifluorostyrene (4), p- cyclopropyltrifluorostyrene (5) and pt-butyltrifluorostyrene (6), have been synthesized. Rateconstants (k_2) of the thermal cyclodimerization of these compounds have been measured in the tem-perature range 120-160 ° C. The polar parameters σ_ (mb) of these TFS’s calculated from ~ (19) F NMR chemi- cal shifts are: for p-thiomethyl, -0.18; cyclopropyl, -0.31 and pt-butyl, -0.22. The spin delo-calization substituent parameters σ’_T (140 °) of p-thiomethyl, cyclopropyl and t-butyl groups are 0.59, 0.27 and 0.30 respectively. These all of these groups act as electron-donating groups which can also effectually stabilize a spin.