烷基通常是邻对位定位基。
Alkyl is an usual ortho & para directing group .
一般而言，RI<0、RC>0、R>0时，取代基是典型的使苯环活化的邻对位定位基；
Generally speaking , when R_I < 0 , R_C > 0 , R > 0 , substituent can activate benzene ring and has p_ and o_position orientation effect ;
邻对位定位基