Which of the following is least reactive in a nucleophilic substitution reaction?
- (CH3)3C-Cl
- CH2=CHCl
- CH3CH2Cl
- CH2=CHCH2Cl
Answer
(2) CH2=CHCl
Solution
As per NCERT, in vinyl chloride CH2=CH-Cl the lone pair of Cl is in resonance with the C=C bond:
CH2=CH- Cl: CH2-CH= Cl
⇒ the C–Cl bond acquires partial double-bond character and the carbon is sp2 (bond shorter and stronger).
∴ It is very difficult to replace Cl by a nucleophile, whereas (CH3)3CCl (SN1), CH3CH2Cl (SN2) and allyl chloride (stable allylic carbocation) react readily.
Answer: (2)