Free Radical Halogenation: Chain Mechanism and Selectivity (Br vs Cl)

Learn free radical halogenation with a step-by-step chain mechanism: initiation, propagation, termination. Understand why bromination is more selective than chlorination and predict major products.

• Reagents: Br2 or Cl2, hv (light) or heat
• Core steps: Initiation → Propagation → Termination
• Selectivity: Br is more selective (prefers 3° > 2° > 1°); Cl is less selective
• Key intermediate: Carbon radical (stability matters)
• Stereochemistry: If a stereocenter forms via planar radical, racemization is common
• Exam type: Predict the major product
• Exam type: Rate / selectivity
• Exam type: Failure modes / distractors