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The rate constants(k_2)of the thermal dimerization of seven substituted trifluorostyrenesin n-hexane solution have been determined in the temperature range 110°—160℃.In general,nogood correlation can be obtained with various Hammett type substituent parameters,e.g.,σ,σ~+,σ~-,σ~0,σ_R,σ_R~+,σ_R~-,and σ_R~0 etc.These results accord with the view that in addition to the polar effects,theabilities of the substituent to delocalize the spin also play important roles in affecting the rates ofdimerizations.Rationalizations for previously reported successful correlations of polar substituentconstants with radical reactions are presented.
The rate constants (k_2) of the thermal dimerization of seven substituted trifluorostyrenesin n-hexane solution have been determined in the temperature range 110 ° -160 ° C. In general, nogood correlation can be obtained with various Hammett type substituent parameters, eg, σ, σ ~ +, σ ~ -, σ ~ 0, σ_R, σ_R ~ +, σ_R ~ -, and σ_R ~ 0 etc. These results accord with the view that in addition to the polar effects, the performance of the substituent to delocalize the spin also play important roles in affecting the rates ofdimerizations.Rationalizations for previously reported successful correlations of polar substituent states with radical reactions are presented.