Free radical halogenation takes place in the presence of light or at high temperature (abov 773K.)
Channel: Doubtnut
Date: 29/03/2020

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 alkyl radicals 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\")` Relative amount = Number of hydrogen atoms on the respective carbon `xx` relative reactivity. NBS (N-bromo succinimide) is used for bromination at allylic and benzylic carbon, whereas `Br_(2)//hv` gives bromination at benzylic allylic and alkyl carbon. Arrange decreasing order of reactivity of given compounds with NBS :(N-bromo succinimide) `I. C_(6)H_(5)-CH_(3)` `II.C_(6)H_(5)-CH_(2)-CH_(2)CH_(3)` `III. C_(6)H_(5)-CH_(2)-CH=CH_(2)` `IV. C_(6)H_(5)-underset(CH_(3))underset(|)(CH)-CH=CH_(2)` Select the correct answer from the codes given below Codes: