SN₂ and SN₁ reactions follow:

Question

Question

This question was previously asked in

DSSSB PGT Chemistry (Female) Official Paper (Held On: 06 Jul, 2018 Shift 1)

Answer 1

CONCEPT:

SN2 and SN1 Reaction Mechanisms

SN2 Reaction (Substitution Nucleophilic Bimolecular):
- This reaction is a one-step mechanism where the nucleophile attacks the substrate and the leaving group departs simultaneously.
- The rate of the SN2 reaction depends on the concentration of both the substrate and the nucleophile.
- Thus, the SN2 reaction follows a second-order rate law.
SN1 Reaction (Substitution Nucleophilic Unimolecular):
- This reaction is a two-step mechanism where the leaving group departs first, forming a carbocation intermediate, followed by the attack of the nucleophile.
- The rate of the SN1 reaction depends only on the concentration of the substrate (formation of the carbocation is the rate-determining step).
- Thus, the SN1 reaction follows a first-order rate law.

EXPLANATION:

The given statement asks about the order of SN2 and SN1 reactions.
From the above concept:
- SN2 reactions follow a second-order rate law (depends on substrate and nucleophile).
- SN1 reactions follow a first-order rate law (depends only on the substrate).
Therefore, the correct answer is: Option 1: Second and first order.

Conclusion: SN2 reactions are second-order, and SN1 reactions are first-order.