Question

Arrange the compounds A, B, C, and D in the increasing order of their reactivity towards SN$_1$ reaction.
A = C$_6$H$_5$CH$_2$Cl
B = C$_6$H$_5$Cl
C = CH$_2$=CH–Cl
D = CH$_3$–CH$_2$–Cl

• A. D<B<A<C
• B. D<C<B<A
• C. B<D<C<A
• D. C<A<D<B

Hint:

In SN\(_1\) reactions, the reactivity depends on the stability of the carbocation formed. Benzyl and allyl halides are generally more reactive due to their ability to stabilize the carbocation through resonance or conjugation.

Answer 1

The Correct Option is C

For an SN\(_1\) reaction, the reactivity is influenced by the stability of the carbocation formed during the reaction. The order of reactivity follows the trend: allyl>benzyl>primary. 

Let’s analyze the compounds: 

- Compound A, C\(_6\)H\(_5\)CH\(_2\)Cl: The benzyl chloride undergoes SN\(_1\) easily due to the resonance stabilization of the benzyl carbocation. It is highly reactive. 
- Compound B, C\(_6\)H\(_5\)Cl: This is a simple aryl chloride, and the carbocation formed is not stabilized by resonance as in the case of benzyl chloride, so it is less reactive. 
- Compound C, CH\(_2\)=CH–Cl: This is an allyl chloride, which can form a resonance-stabilized carbocation. However, the double bond conjugation decreases its reactivity compared to benzyl chloride. 
- Compound D, CH\(_3\)–CH\(_2\)–Cl: This is a primary alkyl chloride, and it forms a primary carbocation, which is the least stable, hence the least reactive. Thus, the order of reactivity towards SN\(_1\) is: \[ B<D<C<A \]