NEET2017ChemistryHaloalkanes and HaloarenesActual
Decreasing order of reactivity in Williamson synthesis of the following : I. Me ₃ CCH ₂ Br II. CH ₃ CH ₂ CH ₂ Br III. CH ₂= CHCH ₂ Cl IV. CH ₃ CH ₂ CH ₂ Cl
Options
- AIII > II > IV > I
- BI > II > IV > III
- CII > III > IV > I
- DI > III > II > IV
Correct answer
C. II > III > IV > I
Step-by-step solution
C - Br bond is weaker than C - Cl bond, therefore, alkyl bromide (II) reacts faster than alkyl chlorides, (III) and (IV). Since CH ₂= CH - is electron withdrawing therefore, CH ₂ has more +ve charge on III than on IV. In other words, nucleophilic attack occurs faster on III than on IV. Further, since Williamson synthesis occurs by S _ N 2 mechanism, therefore, due to steric hindrance alkyl bromide (I) is the least reactive. Thus, the decreasing order of reactivity is II > III > IV > I.