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本文报道全氟异丙基自由基[5(i)]与全氟正丙基自由基[5(n)]的相对形成速度。在50—80℃之间测定了R_FOF(CF_3)[R_F=i-C_3F_7,3(i);R_F=n-C_3F_7,3(n)]自由基β-断裂与攫卤反应的相对比速k_r(i),k_r(n),从而求得了5(i)与5(n)的相对形成速度的比值(k_β(i):k_β(n)]。它们在50℃时为540—680,在80℃时为400—590,此值远远大于碳氢系列自由基的相应比值。最后又计算了3(i)与3(n)的各β-断裂反应活化参数与攫卤反应活化参数差之差,△G~≠(i-n),△H~≠(i-n),△S~≠(i-n)。这些数据表明5(i)形成速度之所以远远大于5(n),熵和焓均起作用,前者可能更为重要。看来,上述熵的差别反映了3(i)的CF_3侧基使分子中若干旋转自由度受到了限制。
This paper reports the relative formation rates of perfluoroisopropyl radical [5 (i)] and perfluoro-n-propyl radical [5 (n)]. The relative speed k_r of the reaction between β-break and snap-off reaction of R_FOF (CF_3) [R_F = i-C_3F_7,3 (i); R_F = n-C_3F_7,3 (n)] was measured at 50-80 ℃. (k_β (i): k_β (n)] of the relative formation velocities of 5 (i) and 5 80 ℃ is 400-590, which is much larger than the corresponding ratio of hydrocarbon radical series.Finally, we calculated the activation parameter of each β-cleavage reaction of 3 (i) and 3 (n) (In), △ S ~ ≠ (in). These data show that the formation rate of 5 (i) is much greater than 5 (n), and the entropy and enthalpy are both It seems that the difference between the above entropies reflects that the side-group CF 3 of 3 (i) limits the number of rotational degrees of freedom in the molecule.