Question

Which of the following is least reactive in a nucleophilic substitution reaction?

• A. $(C{H}_3{)}_{3}C-Cl$
• B. $C{H}_2=CHCl$
• C. $C{H}_{3}C{H}_{2}Cl$
• D. $C{H}_2=CHC{H}_{2}Cl$

Answer 1

Answer: (B)

Chlorine of vinyl chloride $(C{H}_2=CHCI)$ is non-reactive (less reactive) towards nucleophile (in nucleophilic substitution reaction) because it shows the following resonating structure due to $+M$ effect of $-Cl$ atom.
In structure II, $Cl$-atom have positive charge and partial double bond character with $C$ of vinyl group,so it is more tightly attracted towards the nucleus and it does not get replaced by nucleophile in $S_N$ reaction.