自旋离域参数σ_T之研究 3.四种取代α,β,β-三氟苯乙烯的合成和环化二聚反应动力学参数的测定

The Spin Delocalization Substituent Parameters σ_T 3. The Spin-Delocalizing Abilities of the Acetyl and Trimethylsilyl Groups. Synthesis of Fonr Substituted Trifluorostyrenes.

本文报道了四种不同取代的三氟苯乙烯(TFS)的合成和在120-160℃范围内测定了p-Me_3Si和p-CH_3C(O)取代的TFS热环化二聚反应速率常数k_2并计算出相应的Arrhenius参数和活化参数.从^(19)FNMR的化学位移计算出四种取代TFS的极性参数σ~p.并求出其中1和3的取代基自旋离域参数σ_T,说明1和3都是拉电子取代基,它们的σ_p分别为0.14和0.56, 但又是有相当自族离域能力的取代基,在140℃时其σ_T分别为0.29和0.50。

Four substituted α, β, β-trifluorostyrenes(TFS) (1--4) have been synthesized. The rate constants (k_2) of the thermal cyclodimerization of 1 and 3 have been measured in the temperature range 120--160℃. The polar parameters σ~p of the four TFSs calculated from ^(19)F NMR chemical shifts are: for 1, 0.14; 2, -0.01; 3, 0.56 and 4, -0.46. The spin delocalization substituent parameters σ_T of p-trimethyl-silyl and p-acetyl groups are 0.29 and 0.50 respectively. Thus the p-trimethyl-silyl group is an electron attracting group which also can effectively stabilize a spin.