Chapter 10-Elimination Reactions of Alkyl Halides Flashcards
E2 reaction definition
Concerted, one-step reaction in which the proton and halide ion are removed in the same step.
Product of an elimination reaction
Alkene
E1 reaction definition
Two-step reaction in which the alkyl halide dissociates, forming a carbocation intermediate. Then, a base removes a proton from a carbon adjacent to the positively charged carbon.
Primary and secondary alkyl halides undergo ONLY
E2 reactions.
What undergoes both E2 AND E1 reactions?
Tertiary alkyl halides, allylic halides, and benzylic halides.
E2 reaction favored:
HIGH concentration of a STRONG base
E1 reaction favored
Weak base.
Reaction regioselective, major product is more stable Alkene, unless reactants are sterically hindered or the leaving group is poor.
E2
More stable Alkene is (more/less) substituted?
MORE
Zaitsev’s rule
The Alkene formed when a hydrogen is removed from the β-carbon bonded to the fewest hydrogens.
Alkyl substitution (increases/decreases) the stability of a carbocation and (increases/decreases) the stability of a carbanion.
- Increases
2. Decreases
E2 reaction is also stereoselective. Which is favored?
Anti elimination
β-carbon has two hydrogens, then which products will be formed?
Greater yield?
BOTH E and Z products
Greater yield: one with LARGEST groups on opposite sides of the double bond will be formed in greater yield because it’s more stable.
If the β-carbon is bonded only to one hydrogen, then what is formed?
What does its structure depend on?
- Only one Alkene
2. Depends on the structure of alkyl halide
E1 reaction is (blank); the major product is the (blank).
- Regioselective
2. More stable Alkene
