Chapter 5: Dehydrohalogenation (original) (raw)

Dehydrohalogenation of Alkyl Halides

Reaction type: 1,2- or b-Elimination

Summary:

• When heated with strong bases, alkyl halides typically undergo a 1,2-elimination reactions to generate alkenes.
• Typical bases are NaOH or KOH or NaOR or KOR (alkoxide) especially NaOEt or KOtBu in the alcohol as solvent.
• Alkyl halide relative reactivity order : I > Br > Cl > F (nb. elimination of F is rarely used).
• Product distribution:
  • Regioselectivity is usually controlled by the relative stability of the product alkenes (Zaitsev's rule).
  • Stereoselectivity due to the preferred antiperiplanar (180o) arrangment of -H and -X in the transition state.