Chapter 5:
Structure and Preparation of Alkenes.
Elimination Reactions
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 (180
o
) arrangment of -H and -X in the transition state.
