看条件,如果是光照,溴原子取代甲基的氢；如果铁催化,溴原子取代苯环的氢
C6H5CH3 + Br2 =光照= C6H5CH2Br + HBr
C6H5CH3 + Br2 =Fe,加热= C6H4BrCH3 + HBr