Semester 2 • BP202T
Pharmaceutical Organic Chemistry I (BP202T): Mechanisms & Synthesis
Compiled by Dr. M. S. Venkatesh, Ph.D Organic Synthesis
Chapter 1: Nucleophilic Aliphatic Substitution (\(S_N1\) vs \(S_N2\))
Nucleophilic substitution reactions involve the replacement of a leaving group by an electron-rich nucleophile on a tetrahedral \(sp^3\) carbon center.
Comparison Matrix:
| Parameter | \(S_N1\) Mechanism | \(S_N2\) Mechanism |
|---|---|---|
| Kinetics | First order: Rate = k[R-X] | Second order: Rate = k[R-X][Nu⁻] |
| Steps | Two-step via Carbocation | Single-step concerted transition state |
| Substrate Reactivity | 3° > 2° > 1° > Methyl | Methyl > 1° > 2° > 3° |
| Stereochemistry | Racemization (with slight inversion) | Complete Walden Inversion (100%) |
| Solvent Preference | Polar Protic (\(H_2O\), MeOH, EtOH) | Polar Aprotic (DMSO, DMF, Acetone) |
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