Predict the order of reactivity of the following four isomers towards SN2 reaction. (I) CH3CH2CH2CH2Cl (II) CH3CH2CH(Cl)CH3 (III) (CH3)2CHCH2Cl (IV) (CH3)3CCl
- (IV) > (II) > (III) > (I)
- (IV) > (III) > (II) > (I)
- (I) > (II) > (III) > (IV)
- (I) > (III) > (II) > (IV)
Answer
(4) (I) > (III) > (II) > (IV)
Solution
In SN2 reaction the nucleophile attacks from the back side, so the reactivity decreases with increasing steric hindrance: 1 > 2 > 3 .
(I) CH3CH2CH2CH2Cl — 1 , unbranched
(III) (CH3)2CHCH2Cl — 1 , but branched at the β-carbon ⇒ more hindered than (I)
(II) CH3CH2CH(Cl)CH3 — 2
(IV) (CH3)3CCl — 3 , most hindered
∴ Order of reactivity: (I) > (III) > (II) > (IV)
Answer: (4)