Wize University Chemistry Textbook > Organic Chemistry Reactions
Elimination Reactions
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Elimination Reactions
- Like their analogous substitution reaction, E2 and E1 eliminations are named according to their rate determining step, or how many species are present in the transition state
- For E2 eliminations, the transitions state contains both the substrate and the base, so the rate depends on both species
- For E1 eliminations, a carbocation must form first, so the rate depends only on the substrate (and not on the base)
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Factors Which Affect E1/E2 Eliminations
Choice of Base
Strong bases are ideal for E2 reactions.
These are typically alkoxides (NaOEt for example), because they are too reactive for E1 and SN1 reactions.
In addition, since E1 reactions do not depend on the base at all, the presence of a strong base almost always means an E2 will take place.
Bulky, strong bases are ideal for E2 reactions, as they will reduce any substitution side-products.
Substrates for E1
Anytime you are able to stabilize a carbocation, you should be aware that an E1 elimination may occur -But SN1 reactions can also happen!
Predict which elimination mechanism (E1 or E2) is most likely to be operative in the reactions below:
