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1. Prepared by Bill Weigel and Dr. Laurie Starkey
[Version 3.2]
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2. A fully interactive version of this presentation with
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3. These exercises are part of research project being conducted at
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4. D)
For each transformation shown, propose an acceptable reaction mechanism. Be sure to use
proper arrow pushing, and include all lone pairs and formal charges. When more than one
product is possible specify the major product.
A)
B)
C)
BA C D
Check Your Answers
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5. Propose an acceptable reaction mechanism for each of the elimination products in the following
reaction. Be sure to use proper arrow pushing, and include all lone pairs and formal charges.
Which do you expect to be the major product(s)?
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6. Predict the major elimination product(s) in each of the following
reactions.
A)
B)
C)
D)
BA C D
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7. End of Exercises
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8. The next slides contain only the answers. There
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9. Alkene Preparation via Elimination
(Exercise A)
Eliminations can occur via two different mechanisms (E1 vs E2) based on various conditions.
*E2 mechanisms involve three separate arrows occurring in a single step (anti- elimination).
*E1 mechanisms involve first losing a LG to form a carbocation intermediate followed by the
deprotonation of the β-hydrogen.
Return to
Question
The tert-Butoxide anion is a strong base which means that this reaction will occur via the E2
mechanism. The conversion of reactant to product is concerted (single-step) mechanism. In this
reaction, there is only a single β-hydrogen which is abstracted by the base to yield only one possible
elimination product.

10. *The major/minor products are determined by Zaitsev’s Rule.
Major (trisubstituted)
Minor (disubstituted)
Alkene Preparation via Elimination
(Exercise B)
Eliminations can occur via two different mechanisms (E1 vs E2) based on various conditions.
*E2 mechanisms involve three separate arrows occurring in a single step (anti- elimination).
*E1 mechanisms involve first losing a LG to form a carbocation intermediate followed by the
deprotonation of the β-hydrogen.
Return to
Question
Methanol is weakly basic (like water) so this reaction will proceed via the E1 mechanism. The first step
involving the Br LG proceeds very slowly since it leaves behind an unstable primary carbocation.
Rearrangement through hydride shift then occurs extremely quickly to shift the carbocation to a much
more stable tertiary position. Finally, two distinct types of β-hydrogen are deprotonated by the
methanol to generate two products of which the more substituted one is more stable.

11. Minor (monosubstituted)
Major (trisubstituted)
Return to
Question
Hydroxide is a strong base so this reaction will proceed via E2. There are 2 β-hydrogens that each yield
two products of which the more substituted one is more stable.
Alkene Preparation via Elimination
(Exercise C)

12. Minor
(disubstituted)
Major
(tetrasub.)
Return to
Question
Hydroxide is a strong base so this reaction will proceed via E2. There are 2 β-hydrogens that each yield
two products of which the more substituted one is more stable.
Alkene Preparation via Elimination
(Exercise D)

13. Eliminations Involving Alkyl Halides
This problem is based on the wide range of carbocation rearrangements that E1 (and Sn1)
undergo.
*Consider the stability of the carbocation and any hydride/alkyl shifts that may occur.
*Identify and consider elimination of each β-H in any intermediates.
[Very Minor] Unstable carbocation
undergoes fast rearrangement
before elimination can occur
[Minor] Zaitsev’s Rule,
[Minor] Zaitsev’s Rule
[Major] Zaitsev’s Rule,
conjugated with existing
pi-bond
[Major] Zaitsev’s Rule,
conjugated with existing
pi-bond
Vs.
Vs.
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Question

14. Eliminations Involving Alkyl Halides
(Exercise A)
Consider the chemical mechanism (even though only the major product is asked for).
Drawing the whole mechanism out may assist you.
A) NaOH is a strong base (E2) thus rearrangement is not
possible. The most substituted trans product is major.
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Question

15. Eliminations Involving Alkyl Halides
(Exercise B)
Consider the chemical mechanism (even though only the major product is asked for).
Drawing the whole mechanism out may assist you.
B)
Ethanol is a weak base (E1). No favorable
carbocation rearrangement is possible. The most
substituted trans product is major.
Return to
Question

16. Eliminations Involving Alkyl Halides
(Exercise C)
Consider the chemical mechanism (even though only the major product is asked for).
Drawing the whole mechanism out may assist you.
C)
Ethanol is a weak base (E1). Carbocation
rearrangement from 2° to 3° occurs. The most
substituted product of the rearranged
carbocation is major.
Return to
Question

17. Eliminations Involving Alkyl Halides
(Exercise D)
Consider the chemical mechanism (even though only the major product is asked for).
Drawing the whole mechanism out may assist you.
D)
EtO- is a strong base (E2) thus rearrangement is
not possible. The most substituted product is
major.
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Question

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Please click the link below to take a quick 3 minute survey:
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