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芳环亲电取代定位效应是以苯为标准(K_(Sub)/K_B)确定的。它只能笼统说明取代苯对于苯的相对活性,而不能具体说明不同位置活性的大小。教学中有必要引入下面一些定量化的概念。一、分速度因数(f)和选择性因数(S_f)。 (1)式中“6”为苯分子里可被取代的氢数;y为取代苯分子里可被取代的氢数(对位为1,邻间位各为2);Z为取代产物的异构体比例。
Aromatic ring electrophilic substitution of the positioning effect is based on the standard benzene (K Sub (/ K_B)). It can only be a general description of the relative benzene benzene for the relative activity, but can not specify the size of the activity at different locations. It is necessary to introduce the following quantitative concepts in teaching. First, the sub-speed factor (f) and selectivity factor (S_f). (1) where “6” is the number of hydrogens that can be substituted in the benzene molecule; y is the number of hydrogens that can be substituted in the substituted benzene molecule (para-position is 1 and each para-position is 2); Z is the Isomer ratio.