CHEM 210 [CHAPTER 7: ELIMINATION REACTIONS OF ALKYL HALIDES 1 Fall 2013 Elimination Reactions – A Review of Concepts 1. Alkenes 1. For each of the following sets of alkenes rank them in order of increasing stability: a. b. c. 2. E2 2. For each of the following E2 reactions draw the mechanism to afford the illustrated product: 3. Carefully read the following mechanism and draw the alkene produced. Is the mechanism E1 or E2? 4. When (R)3bromo2,3dimethylpentane is treated with sodium hydroxide, four different alkenes are formed. Draw all four products and rank them in order of increasing stability. Circle the major product. 5. When 3bromo2,4dimethylpentane is treated with sodium hydroxide, only one alkene formed. Draw the product and explain.
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CHEM 210 [CHAPTER 7: ELIMINATION REACTIONS OF ALKYL HALIDES
1 Fall 2013
Elimination Reactions – A Review of Concepts
1. Alkenes 1. For each of the following sets of alkenes rank them in order of increasing stability:
a.
b.
c.
2. E2 2. For each of the following E2 reactions draw the mechanism to afford the illustrated product:
3. Carefully read the following mechanism and draw the alkene produced. Is the mechanism E1 or E2?
4. When (R)-‐3-‐bromo-‐2,3-‐dimethylpentane is treated with sodium hydroxide, four different alkenes are formed. Draw all four products and rank them in order of increasing stability. Circle the major product.
5. When 3-‐bromo-‐2,4-‐dimethylpentane is treated with sodium hydroxide, only one alkene formed. Draw the product and explain.
CHEM 210 [CHAPTER 7: ELIMINATION REACTIONS OF ALKYL HALIDES
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6. E2 reactions exhibit second order kinetics. Consider the reaction below and answer the questions:
a. What happens to the rate if the concentration of: b. Chlorocyclopentane is tripled and sodium hydroxide remains the same? c. Chlorocyclopentane remains the same and sodium hydroxide is doubled? d. Chlorocyclopentane is doubled and the concentration of sodium hydroxide tripled?
7. Arrange each set of compounds in order of increasing E2 reactivity:
8. Identify the major and minor products of the following E2 reactions:
9. Identify an alkyl halide that could be used to make the following alkene by E2:
CHEM 210 [CHAPTER 7: ELIMINATION REACTIONS OF ALKYL HALIDES
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10. For the following chiral molecules, draw the products of E2:
11. When menthyl chloride is treated with strong base, only one E2 product is observed. Yet, when neomenthyl
chloride is treated with strong base, two E2 products are observed. Draw the products and explain.
12. Predict which of the following alkyl halides undergo E2 more rapidly. Why?
13. Identify the sole product of the following reaction:
CHEM 210 [CHAPTER 7: ELIMINATION REACTIONS OF ALKYL HALIDES
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14. Indicate the products of the following E2 reactions:
15. In each of the following cases draw the structure of an alkyl halide that will undergo an E2 process to yield ONLY the indicated alkene:
CHEM 210 [CHAPTER 7: ELIMINATION REACTIONS OF ALKYL HALIDES
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3. E1 16. Identify the major and minor products for the following E1 reactions (do not draw SN1 products yet):
17. Draw a mechanism for each of the following E1 reactions:
18. Consider the following reaction:
a. How would the rate be affected if the concentration of tert-‐butyl bromide were doubled? b. How would the rate be affected if the concentration of ethanol were doubled?
19. Draw the carbocation intermediates that would be formed if these alkyl halides were to undergo E1/SN1.
Classify each as 1o, 2o or 3o. One of these won’t undergo E1/SN1, why?
20. Predict which of the following will undergo E1/SN1 more rapidly. Why?
CHEM 210 [CHAPTER 7: ELIMINATION REACTIONS OF ALKYL HALIDES
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KEY 1. For each of the following sets of alkenes rank them in order of increasing stability:
a.
b.
c.
2. For each of the following E2 reactions draw the mechanism to afford the illustrated product:
3. The mechanism is E2.
CHEM 210 [CHAPTER 7: ELIMINATION REACTIONS OF ALKYL HALIDES
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4. When (R)-‐3-‐bromo-‐2,3-‐dimethylpentane is treated with sodium hydroxide, four different alkenes are formed. Draw all four products and rank them in order of increasing stability. Circle the major product.
5. Two identical β -‐hydrogens lead to same product:
6. E2 reactions exhibit second order kinetics.
a. 3x faster b. 2x faster c. 6x faster
7. Arrange each set of compounds in order of increasing E2 reactivity:
CHEM 210 [CHAPTER 7: ELIMINATION REACTIONS OF ALKYL HALIDES
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8. Identify the major and minor products of the following E2 reactions:
CHEM 210 [CHAPTER 7: ELIMINATION REACTIONS OF ALKYL HALIDES
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9. Identify an alkyl halide that could be used to make the following alkene by E2:
10. For the following chiral molecules, draw the products of E2:
11. Check for available anti-‐periplanar protons in each case:
CHEM 210 [CHAPTER 7: ELIMINATION REACTIONS OF ALKYL HALIDES
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12. Because of the bulky tert-‐butyl group, the first compound is essentially locked in a chair conformation in which the chlorine occupies an equatorial position. This conformation cannot undergo an E2 reaction because the leaving group is not antiperiplanar to a proton. However, the second compound is locked in a chair conformation in which the chlorine occupies an axial position. This conformation rapidly undergoes an E2 reaction. Therefore, the second compound is expected to be more reactive towards an E2 process than the first compound.
13. Identify the sole product of the following reaction:
14. Indicate the products of the following E2 reactions:
CHEM 210 [CHAPTER 7: ELIMINATION REACTIONS OF ALKYL HALIDES
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15. In each of the following cases draw the structure of an alkyl halide that will undergo an E2 process to yield ONLY the indicated alkene:
16. Identify the major and minor products for the following E1 reactions (do not draw SN1 products yet):
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17. Draw a mechanism for each of the following E1 reactions:
18. Consider the following reaction:
a. Rate would double b. No change – not in rate equation!
CHEM 210 [CHAPTER 7: ELIMINATION REACTIONS OF ALKYL HALIDES
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19. Primary will not undergo E1.
20. In the second compound the carbocation would be resonance stabilized:
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