Understanding chemical reactions and their mechanisms is central to designing and optimizing drug candidates. This section explores how medicinal chemists use mechanistic insight to build molecules with precision, efficiency, and purpose.

1. Reaction Types in Medicinal Chemistry

• Substitution reactions (e.g., SN1, SN2) for modifying functional
  groups
• Elimination and addition reactions to build or remove unsaturation.
• Oxidation/reduction reactions for tuning polarity and metabolic stability
• Cycloadditions and pericyclic reactions for constructing
  complex ring systems
• Cross-coupling reactions (e.g., Suzuki, Buchwald–Hartwig) for C–C and C–N bond formation — essential in modern drug synthesis

2. Mechanistic Thinking

• How understanding electron flow, intermediates, and transition
  states helps predict reactivity and selectivity
• Using curved-arrow notation to rationalize transformations and troubleshoot failed reactions

3. Reaction Optimization

• Tuning reagents, catalysts, solvents, and temperature to improve yield, selectivity, and scalability.
• Applying kinetic vs thermodynamic control to steer product
  outcomes

4. Mechanism-Guided Design

• Designing molecules that exploit enzyme mechanisms (e.g., covalent inhibitors, transition-state analogs).
• Using bioisosteres and prodrugs to modulate reactivity and
  improve pharmacokinetics