The rate constants (k) of the homo-cycloaddition reactions of five substituted α, β, β-tri- fluorostyrenes (TFS’s), i.e. p-nitrotrifluorostyrene (4), p-cyanotrifluorostyrene (5), p-carbomethoxytri- fluorostyrene (...The rate constants (k) of the homo-cycloaddition reactions of five substituted α, β, β-tri- fluorostyrenes (TFS’s), i.e. p-nitrotrifluorostyrene (4), p-cyanotrifluorostyrene (5), p-carbomethoxytri- fluorostyrene (6), p-carboxytrifluorostyrene (7) and p-carbamyltrifluorostyrene (8), have been measured in the temperature range of 110-160℃. The ~σmb polar substituent parameters of these TFS's cal- culated from ^(19) F NMR chemical shifts are: NO_2, 0.86; CN, 0.86; CO_2CH_2, 0.40; CO_2H, 0.31; CONH_2, 0.10. The spin delocalization substituent parameters ~σT of NO_2, CN, CO_2 CH_2, CO_2H and CONH_2 are 0.32, 0.38, 0.31, 0.37 and 0.37 respectively. Thus all these electron-pair attracting groups are also very effective spin-stabilizers.展开更多
基金Project supposed by the National Natural Science Foundation of China
文摘The rate constants (k) of the homo-cycloaddition reactions of five substituted α, β, β-tri- fluorostyrenes (TFS’s), i.e. p-nitrotrifluorostyrene (4), p-cyanotrifluorostyrene (5), p-carbomethoxytri- fluorostyrene (6), p-carboxytrifluorostyrene (7) and p-carbamyltrifluorostyrene (8), have been measured in the temperature range of 110-160℃. The ~σmb polar substituent parameters of these TFS's cal- culated from ^(19) F NMR chemical shifts are: NO_2, 0.86; CN, 0.86; CO_2CH_2, 0.40; CO_2H, 0.31; CONH_2, 0.10. The spin delocalization substituent parameters ~σT of NO_2, CN, CO_2 CH_2, CO_2H and CONH_2 are 0.32, 0.38, 0.31, 0.37 and 0.37 respectively. Thus all these electron-pair attracting groups are also very effective spin-stabilizers.
