Question

Give two differences between N1 and N2 reactions.

Hint:

To remember which is which: has 1 reactant in the rate-determining step but 2 steps. N2 has 2 reactants in the rate-determining step but only 1 step!

Answer 1

Concept:
Nucleophilic substitution reactions (SN1 and SN2) are classified based on their kinetics and mechanism.

SN1 (Substitution Nucleophilic Unimolecular): The rate depends only on the concentration of the substrate.
SN2 (Substitution Nucleophilic Bimolecular): The rate depends on the concentration of both the substrate and the nucleophile.

Step 1: Differences between SN1 and SN2 reactions.

SN1 Reaction:
Number of steps: Two-step process.
Intermediate: Carbocation intermediate is formed.
Kinetics: First order, Rate = k[RX].
Stereochemistry: Racemization occurs.

SN2 Reaction:
Number of steps: Single-step (concerted) process.
Intermediate: No intermediate; only a transition state is formed.
Kinetics: Second order, Rate = k[RX][Nu⁻].
Stereochemistry: Walden inversion occurs.

Step 2: Reactivity order.
SN1 preference: Tertiary (3°) > Secondary (2°) > Primary (1°).
SN2 preference: Primary (1°) > Secondary (2°) > Tertiary (3°).