3.间位定位基
当苯环上的取代基为－NO2、－SO3H、－SO2R、－COOH、－COOR、－CHO、－COR、－CN等时，使苯环钝化，但邻位和对位钝化程度较间位大，在取代反应中，新取代基大多进入间位，形成间位异构体。这类取代基称为有钝化作用的间位取代基。
如硝基苯在发烟硝酸、发烟硫酸存在下，长时间加热，可以制得少量的间硝基苯( )，同时比较硝基苯的制法可以看出，硝基的引入使苯的活性降低，反应的条件明显提高。
2.邻对位定位基团--苯的活性减弱
当苯环上连接有卤素原子(－F、－Cl、－Br、－I)－CH2Cl、－CH＝CH－等基团时，苯环的反应活性降低，这类反应比较特殊，往往需要在特殊溶剂、催化剂条件下才可能发生反应。
苯环上有连接有不同的基团或官能团，当进一步引入基团时，其引入的位置与原有官能团(基团)有关，而且不同的基团，还会使苯环的反应活性发生较大的变化。
1.邻对位定位基团，苯环的活性增强
当苯环上连接烃基(甲基、乙基、苯基等)、氨基(－NH2、－NHR、-NR2，R为烷基)、羟基(－OH)、烷氧基(－OCH3、－OC2H5)等基团，使苯的反应活性增强，新引入的基团进入原基团的邻对位位置。
教材上制备硝基苯需要在浓硫酸、浓硝酸混酸与苯在55℃条件下制得，而通常只能得到，很难得到二硝基化合物。
甲苯中新引入的－NO2均处于甲基(－CH3)的邻位或对位。在过量硝酸存在下，很容易得到三硝基化合物(TNT)，这也看出甲基提高了苯环的活性。
30．(四川省成都市新都区2010届高中毕业班诊断性考试)
To my great surprise, yesterday, he asked me a few questions there were no answers.
A．to which B．about which C．in which D．on which
答案 A
29．(山东省临沂市2010届高三上学期期中考试)
The jouney around the world took the old sailor nine months, ________ the sailing time was 226 days.
A. from that B. during that C. of which D. for which
答案 C
28．(江苏省镇江市2010届高三12月调研)
Finally the manager adopted the best proposal ______ had been put forward at the meeting.
A. which B. that C. what D. as
答案 B
27．(湖南省师大附中2010届高三第四次月考)
We have gathered nearly 100,000 quilts, ___ up to half have gone to the flood-hit areas.
A. with which B. in which C. for which D. of which
答案 D
26．(浙江省诸暨中学2010届高三上学期期中考试)
Every time he tries to break a record, he reaches a point ______ he feels he cannot physically do any more.
A. what B. which C. where D. that
25．(浙江省菱湖中学2010届高三上学期期中考试)
The room _____________ door is painted green is our headmaster’s office.
A. whose B. its C. which D. of which
24．(陕西省临渭区2010届高三第一次适应性调研测试)
It was in Shaanxi Normal University I studied I had a seed knowledge of life skills．
A．that：that B．which；where
C．where；which D．where；that