1

Homework Chapter 18—Ethers and Epoxides; Thiols and Sulfides

Problems with yellow highlight are mandatory homework; the rest are optional but

recommended.

Drawing Instructions: Draw structures corresponding to each of the given names.

1. Draw: tetrahydrofuran

ANS:

2. Draw: 12-crown-4

ANS:

3. Draw: 1-isopropoxycyclopentene

ANS:

4. Draw: allyl benzyl ether

ANS:

5. Draw: diethyl ether

ANS: CH3CH2−O−CH2CH3

Ethers and Epoxides; Thiols and Sulfides

2

6. Draw: 3-methyl-1-butanethiol

ANS:

7. Draw: cyclopropyl ethyl sulfide

ANS:

IUPAC Naming Instructions: Provide proper IUPAC names.

8. Name:

ANS: m-chloroanisole or m-chloromethoxybenzene or (m-chlorophenyl) methyl ether

9. Name:

ANS: 1-ethoxy-2,2-dimethylpropane or ethyl neopentyl ether

10. Name:

ANS: dicyclohexyl sulfide

Chapter 18

3

Ethers and Epoxides; Thiols and Sulfides

4

Exhibit 18-1 Consider the reaction below to answer the following question(s).

11. Refer to Exhibit 18-1. Write the complete stepwise mechanism for the reaction. Show all

intermediate structures and all electron flow with arrows.

ANS:

12. Refer to Exhibit 18-1. Mechanistically, the Williamson ether synthesis outlined above is: a. an E1 process b. an SN1 process c. an E2 process d. an SN2 process

ANS: d

13. Refer to Exhibit 18-1. Alternatively, cyclopentyl methyl ether may be synthesized from

cyclopentene. Outline a synthesis of cyclopentyl methyl ether from cyclopentene.

ANS:

14. Diphenyl ether is inert to cleavage by HI or HBr. Explain.

Chapter 18

5

ANS: Acidic ether cleavages are typical nucleophilic substitution reactions that take place by either an SN1 or SN2 pathway. Diaryl ethers like diphenyl ether are inert under ordinary acidic conditions because the generation of an aryl cation is an SN1 process that is energetically unfavorable, and "back-side" attack at the ring carbon bound to oxygen is sterically unfavorable.

15. Write the complete stepwise mechanism for the reaction below. Show all electron flow with

arrows and draw all intermediate structures.

ANS:

Exhibit 18-2 Consider the data below to answer the following question(s). Acetals are a special class of ethers which have two ether linkages at a single carbon. Tetrahydropyranyl ethers are acetals that are easily cleaved with mild aqueous acids at room temperature to yield alcohols.

Ethers and Epoxides; Thiols and Sulfides

6

16. Refer to Exhibit 18-2. Draw arrows showing the electron flow for this reaction on the structures provided below.

ANS:

17. Refer to Exhibit 18-2. This ether cleavage occurs so easily under such mild conditions

because the carbocation intermediate in step two is very stable. Explain why this carbocation is stabilized.

ANS: The carbocation generated in the first step of the SN1 process is resonance-stabilized by the adjacent oxygen lone pairs.

Chapter 18

7

18. When 1,2-epoxypropane is treated with sodium ethoxide in ethanol 1-ethoxy-2-propanol is the major product while only a trace amount of 2-ethoxy-1-propanol is produced. Explain these results based on the reaction mechanism.

ANS: Basic nucleophiles like ethoxide react with epoxides in a typical SN2-type process, so attack takes place at the less hindered epoxide carbon.

Exhibit 18-3 Consider the data below to answer the following question(s). Epoxides are synthesized industrially in one step by silver oxide air oxidation of ethylene and on a laboratory scale in one step by treating an alkene with m-chloroperoxybenzoic acid. An alternative two step process converts alkenes to halohydrins, which are converted by treatment with base to epoxides.

19. Refer to Exhibit 18-3. Show electron flow with arrows on the structures provided below for

each step in the above transformation.

Ethers and Epoxides; Thiols and Sulfides

8

ANS:

20. Refer to Exhibit 18-3. The synthesis of epoxides by base treatment of halohydrins is an

example of an intramolecular: a. SN1 reaction b. hydrolysis reaction c. dehydration reaction d. Williamson ether synthesis

ANS: d

Exhibit 18-4 Propose structure(s) for the starting material(s), reagent(s), or major organic product(s) of the following reactions or sequences of reactions. Show all relevant stereochemistry.

21.

ANS:

Chapter 18

9

22.

ANS:

23.

ANS:

24.

ANS:

Ethers and Epoxides; Thiols and Sulfides

10

25.

ANS:

26.

ANS:

27.

ANS:

Chapter 18

11

28.

ANS:

29.

ANS:

30.

ANS:

Ethers and Epoxides; Thiols and Sulfides

12

31.

ANS:

32.

ANS:

33.

ANS:

34.

Chapter 18

13

ANS:

35. Propose a synthesis of 1,4-dioxane, starting from 1,2-dibromoethane as the only source of

carbon.

ANS:

36. Choose the best reagent for carrying out the following reactions from the list below. Place

the letter of the reagent(s) in the box over the reaction arrow. Use only one letter per box.

A. NaH, then CH3I B. NaOCH3, CH3OH C. m-ClC6H4CO3H D. CH3MgBr in ether, then H3O+

E. warm H2SO4/H2O F. Hg(O2CCF3)2, CH3OH G. H2/Pd H. PCC, CH2Cl2 I. Cl2, H2O J. LiAlH4 in ether, then H3O+

Ethers and Epoxides; Thiols and Sulfides

14

ANS:

37. Complete the synthetic sequence below by drawing the structures of the reaction in the

boxes provided.

Chapter 18

15

ANS:

38. Show how the ether below could be prepared from toluene and any other necessary reagents.

Show all reagents and all intermediate structures.

ANS:

39. Propose a synthesis for the following compound using benzene or toluene and any other

reagents necessary. Show all major intermediate compounds that would probably be isolated during the course of your synthesis.

Ethers and Epoxides; Thiols and Sulfides

16

ANS:

40. Name the compound shown below. Atoms other than carbon and hydrogen are labeled.

ANS: Ethyl hexyl ether or 1-ethyoxyhexane

41. Name the following compound. Atoms other than carbon and hydrogen are labeled.

ANS: o-mercaptotoluene

Chapter 18

17

42. Predict the product of the following reaction.

ANS:

43. Draw the structure of the ether that could be used to produce the following compound

.

ANS: