Free radical halogenation takes place in the presence of light or at high temperature (abov 773K.) Formation of halogen free radical intermediate takes place in first step called chain initiation step. CI_(2)overset(hv)(to)2CI This reaction is mainly given by those compound which have atleast one hydrogen atom present at sp^(3)-hybrid carbon. Reactivity of sp^(3)-hybrid carbon depends on the reactivity of reaction intermediate. The relative rate of formation of alkylradicals by a chlorine radical is : underset((5))("Tertiary") gt underset((3.8))("Secondary") gt underset((1))("Primary") " Percentage yield of the prodcut "=("Relative amount"xx100)/("Sum of relative amounts") Relativeamount = Number of hydrogen atoms on the respective carbon xx relative reactivity. NBS (N-bromo succinimide) is used for bromination at allylic andbenzylic carbon, whereas Br_(2)//hv gives brominationat benzylic allylic and alkyl carbon. Chlorinating agent for free radical chlorination may be taken as :