JEE Advanced High-Yield Revision Notes
Subject: Organic Chemistry | Topic: Nucleophilic Substitution (SN1 vs SN2)
Why is this the hardest & highest-weightage part?
Organic Chemistry (Mechanism portion) confuses 95% of JEE aspirants because questions are
never direct. One wrong step in identifying the nucleophile or solvent changes the entire product,
leading directly to negative marking. Master this table, and you unlock 15-20 marks in JEE
Advanced.
1. Core Comparison: SN1 vs SN2 Mechanisms
Property SN1 Mechanism SN2 Mechanism
Kinetics & Rate First Order: Rate = k[Alkyl Halide] Second Order: Rate = k[Alkyl
Independent of nucleophile Halide][Nucleophile]
strength.
Steps 2-Step Process (via Carbocation 1-Step Concerted Process (via
Intermediate). Transition State).
Substrate 3° > 2° >> 1° (Based on carbocation 1° > 2° >> 3° (Based on minimal
Reactivity stability). steric hindrance).
Stereochemistry Racemization (Both inversion & Walden Inversion (100% backside
retention occur because attack only).
carbocation is planar).
Solvent Polar Protic (e.g., H2O, EtOH, Polar Aprotic (e.g., DMSO, DMF,
Required CH3COOH) to stabilize carbocation. Acetone) to keep nucleophile
naked/reactive.
Rearrangement Possible (Hydride/Methyl shift to Not Possible (No intermediate
form more stable carbocation). formed).
JEE Advanced Ultimate Revision Notes | Organic Chemistry Page 1
Subject: Organic Chemistry | Topic: Nucleophilic Substitution (SN1 vs SN2)
Why is this the hardest & highest-weightage part?
Organic Chemistry (Mechanism portion) confuses 95% of JEE aspirants because questions are
never direct. One wrong step in identifying the nucleophile or solvent changes the entire product,
leading directly to negative marking. Master this table, and you unlock 15-20 marks in JEE
Advanced.
1. Core Comparison: SN1 vs SN2 Mechanisms
Property SN1 Mechanism SN2 Mechanism
Kinetics & Rate First Order: Rate = k[Alkyl Halide] Second Order: Rate = k[Alkyl
Independent of nucleophile Halide][Nucleophile]
strength.
Steps 2-Step Process (via Carbocation 1-Step Concerted Process (via
Intermediate). Transition State).
Substrate 3° > 2° >> 1° (Based on carbocation 1° > 2° >> 3° (Based on minimal
Reactivity stability). steric hindrance).
Stereochemistry Racemization (Both inversion & Walden Inversion (100% backside
retention occur because attack only).
carbocation is planar).
Solvent Polar Protic (e.g., H2O, EtOH, Polar Aprotic (e.g., DMSO, DMF,
Required CH3COOH) to stabilize carbocation. Acetone) to keep nucleophile
naked/reactive.
Rearrangement Possible (Hydride/Methyl shift to Not Possible (No intermediate
form more stable carbocation). formed).
JEE Advanced Ultimate Revision Notes | Organic Chemistry Page 1
