alkenes organic chemistry, Exercises for Chemistry
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alkenes organic chemistry, Exercises for Chemistry

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Chapter 1 – Structure and Bonding

Chapter 7 – Alkenes: Reactions and Synthesis

To answer the questions below consider the following reaction:

When cyclohexene reacts with chlorine in carbon tetrachloride the trans-dihalide is formed.

CCl4

Cl2 Cl

Cl

1. Write the complete stepwise mechanism for this reaction. Be sure to show all intermediate structures and all electron flow using arrows.

Answer:

ClCl

H

H

Cl Cl

Cl

Cl

2. Since the two chlorine atoms add to opposite faces of the cyclohexene double bond, we say that the reaction occurs with:

a. syn stereochemistry b. cis stereochemistry c. anti stereochemistry d. retention of stereochemistry

Answer: c

3. The observed stereochemistry of addition of chlorine to cyclohexene is explained by the intermediacy of a:

a. cyclonium ion b. carbocation c. carbene d. chloronium ion

Answer: d

4. Provide the IUPAC name for the product of the reaction of cyclohexene with bromine.

Answer: trans-1,2-dichlorocyclohexane

5. Draw both chair conformations of trans-1,2-dichlorocyclohexane on the templates provided below. Circle the least stable conformation.

50 Chapter 7: Alkenes: Reactions and Synthesis

1

1

2 2

Answer:

Cl

Cl

Cl Cl

1

1

2 2

Consider the reaction sequence below to answer the following questions:

HgOAc

OH

+ HOAc

Hg(OAc)2, H2O/THF NaBH4

OH

Hg+

6. Write the complete reaction mechanism for the first step of this reaction sequence. Show all electron flow with arrows and show all intermediate structures.

Answer:

HgOAc

OH

+ HOAc

Hg

H H

H OAc

+

O H H

HgOAc

+

Hg OAc

OAc

OAc

H2O

OAc

7. The intermediate in the first step of this reaction sequence is called a:

a. carbocation b. cyclonium ion c. mercurinium ion d. mercapto species.

Answer: c

8. In the second step of this reaction sequence, the organomercury compound is treated with sodium borohydride, NaBH4, to yield the alcohol product. This replacement of a carbon-mercury bond with a carbon-hydrogen bond is termed:

a. an oxidation b. a reduction c. a hydroxylation d. a cycloaddition

Answer: b. 51 Chapter 7: Alkenes: Reactions and Synthesis

Consider the reaction below to answer the following questions.

Alkenes may be hydrated by the hydroboration/oxidation procedure shown.

9. The intermediate formed in the first step of this reaction is:

Answer: b

10. Hydroboration of alkenes is an example of:

a. a rearrangement reaction. b. a substitution reaction. c. an elimination reaction. d. an addition reaction.

Answer: d

11. Hydroboration/oxidation of alkenes occurs with:

a. anti stereochemistry. b. trans stereochemistry. c. syn stereochemistry. d. unpredictable stereochemistry.

Answer: c

12. The regiochemistry of hydroboration/oxidation of alkenes is:

a. Markovnikov. b. non-Markovnikov c. subject to solvent effects. d. unrelated to alkene structure.

Answer: b

Test Items for McMurry’s Organic Chemistry, Sixth Edition 52

CH3 1. BH3, THF 2. H2O2, NaOH, H2O

H OH CH3

H

B

CH3

H H

H

_

a. b.

c. d.

BH2H

H

CH3

OHH

BH2

CH3

OHH2B

H

CH3

Consider the reaction below to answer the following questions.

When dichlorocarbene is generated in the presence of an alkene, a dichlorocyclopropane is formed.

13. Write the complete stepwise mechanism for the formation of dichlorocarbene, :CCl2. Show all intermediate structures and show all electron flow with arrows.

Answer:

14. Draw the complete Lewis electron dot structure for dichlorocarbene, :CCl2.

Answer:

15. In the reaction of an alkene with dichlorocarbene, the dichlorocarbene is the:

a. electrophile. b. Lewis base. c. nucleophile. d. both b and c.

Answer: a

16. The reaction of an alkene with dichlorocarbene is:

a. regiospecific. b. Markovnikov. c. stereospecific. d. non-Markovnikov.

Answer: c

The sequence of (1) alkene hydroxylation followed by (2) diol cleavage is often an excellent alternative to direct alkene cleavage with ozone. For this sequence below, answer the following questions.

17. Draw the structure of A.

Answer:

18. Give the formula for reagent B.

Answer: HIO4 53 Chapter 7: Alkenes: Reactions and Synthesis

H3C

C C

CH3

HH

CHCl3 KOH H3C

H H CH3

ClCl

+

Cl C Cl

CH3 1. OsO4, pyridine

2. NaHSO3, H2O A

B

CH3

O

H

O

OH

CH3 OH

H

++ + KClC

Cl

Cl

K+K+ H2O _

Cl C

Cl

Cl

_ OHC

Cl

Cl

Cl

H

Predict the products of each reaction below. Indicate regiochemistry and stereochemistry when relevant.

19.

Answer:

20.

Answer:

21.

Answer:

22.

Test Items for McMurry’s Organic Chemistry, Sixth Edition 54

CH3

CH3

H2

Pd

CH3

CH3

H2

Pd

CH3

H

CH3 H

H3C

C C

H

CH3H

CHCl3 KOH

H3C

C C

H

CH3H

CHCl3 KOH

ClCl

H H3C

CH3 H

CH3

H H3O

+

THF, heat

CH3

H H3O

+

THF, heat

CH3

CH CH2 Cl2 H2O

Answer:

23.

Answer:

24.

Answer:

25.

Answer:

55 Chapter 7: Alkenes: Reactions and Synthesis

OH

OH

HIO4 H2O

OH

OH

HIO4 H2O

H H

O O

CH CH2 Cl2 H2O

CH

OH

CH2Cl

C C

H H 1. OsO4, pyridine 2. NaHSO3, H2O

C C

H H 1. OsO4, pyridine 2. NaHSO3, H2O

C CH H

OHHO

CH3 Cl2

CCl4

CH3 Cl2

CCl4

CH3 Cl

H

Cl

26.

Answer:

27.

Answer:

28.

Answer:

29.

Answer:

Test Items for McMurry’s Organic Chemistry, Sixth Edition 56

H

C C

H

CH3H3C

CH2I2 Zn(Cu), ether

H

C C

H

CH3H3C

CH2I2 Zn(Cu), ether

H3C CH3 H H

1. O3, CH2Cl2 2. Zn, HOAc

1. O3, CH2Cl2 2. Zn, HOAc

O

H

O

+

Br KOH

ethanol

Br KOH

ethanol

1. Hg(OAC)2, H2O 2. NaBH4

1. Hg(OAC)2, H2O 2. NaBH4

OH

30.

Answer:

31.

Answer:

Choose the best reagent from the list below for carrying out each transformation. Place the letter of the reagent in the blank to the left of the reaction.

a. 1. O3 e. 1. OsO4 2. Zn, H3O+ 2. NaHSO3, H2O

b. 1. BH3, THF f. KMnO4, acid 2. H2O2, NaOH, H2O

c. CHCl3, KOH g. CH2I2, Zn(Cu)

d. H2O, H2SO4, heat h. 1. Hg(OAc)2, H2O 2. NaBH4

32.

Answer: b

33.

57 Chapter 7: Alkenes: Reactions and Synthesis

CH3 KMnO4 H3O

+

CH3 KMnO4 H3O

+ HO

O

O

H2C CHCl ROOR heat

CH2 CH

Cl

CH2 CH

Cl

CH2 CH

Cl

( )

CH3 CH3

OH

CH3 H

O

O

CH3

(polymer segment) heat

ROORH2C CHCl

Answer: a

34.

Answer: g

35.

Answer: h

For each reaction below suggest structures for alkenes that give the indicated reaction products. There may be more than one answer in some cases.

36.

Answer:

37.

Answer:

Test Items for McMurry’s Organic Chemistry, Sixth Edition 58

CH3 CH3

H

CH3 CH3

OH

H2 Pd

or or

1. BH3, THF 2. H2O2, NaOH, H2O

OH

38.

Answer:

39.

Answer:

To answer the questions below consider the following information:

In an abandoned laboratory has been found a flammable liquid, A, in a bottle bearing only the label “Compound A: C H7 12 .” Government agents have offered you a considerable sum to determine the structure of this compound. After verifying the molecular formula by elemental analysis, you find that Compound A reacts with 1 mol equiv of hydrogen and, after treatment with acidic KMnO4 , gives the dicarboxylic acid C (see below). Another bottle from the same laboratory is labeled “Compound B (isomer of A).” Compound B also reacts with 1 mol equiv of hydrogen, but yields cyclohexanone after treatment with acidic KMnO4 .

40. How many degrees of unsaturation does Compound A possess?

Answer: A saturated seven carbon compound should have the formula C7H16 so compound A has 16 12 2 2−( ) ÷ = degrees of unsaturation.

59 Chapter 7: Alkenes: Reactions and Synthesis

HBr ether

Br

or

HO C

O

CHCH2CH2CH2

CH3

C

O

OH

Compound C

O

cyclohexanone

ROOR heat

CH2CHCH2CHCH2CH

C6H5 C6H5 C6H5

( )n

CH2 CHC6H5

41. Suggest structures for A and B.

Answer:

42. What was the other product formed in the KMnO4 oxidation of B?

Answer: CO2

43. Lyapolate Sodium, whose structure is shown below, is used as an anticoagulant. Identify the monomer unit(s) in lyapolate sodium.

Answer:

44. Povidone is produced commercially as a series of products having mean molecular weights ranging from about 10,000 to 700,000. Complexed with iodine, povidone yields an iodophor, marketed under the tradename Betadine, which is used as a topical anti-infective.

Identify the monomer unit(s) in povidone.

Answer:

Test Items for McMurry’s Organic Chemistry, Sixth Edition 60

CH3 CH2

Compound A Compound B

CH2 CH CH2 CH

SO3NaSO3Na

( ) n

H2C CH SO3Na

CH CH2 CH CH2

N NO O

( )n

N O

CH CH2

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