Homework Chapter 18 Ethers and Epoxides; Thiols and Sulfides

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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 2. Draw: 12-crown-4 3. Draw: 1-isopropoxycyclopentene 4. Draw: allyl benzyl ether 5. Draw: diethyl ether CH 3 CH 2 O CH 2 CH 3 1

2 Ethers and Epoxides; Thiols and Sulfides 6. Draw: 3-methyl-1-butanethiol 7. Draw: cyclopropyl ethyl sulfide IUPAC Naming Instructions: Provide proper IUPAC names. 8. Name: m-chloroanisole or m-chloromethoxybenzene or (m-chlorophenyl) methyl ether 9. Name: 1-ethoxy-2,2-dimethylpropane or ethyl neopentyl ether 10. Name: dicyclohexyl sulfide 2

3 Chapter 18 3

4 Ethers and Epoxides; Thiols and Sulfides Exhibit 18-1 Consider the reaction below to answer the following question(s). 11. Refer to Exhibit Write the complete stepwise mechanism for the reaction. Show all intermediate structures and all electron flow with arrows. 12. Refer to Exhibit Mechanistically, the Williamson ether synthesis outlined above is: a. an E1 process b. an S N 1 process c. an E2 process d. an S N 2 process d 13. Refer to Exhibit Alternatively, cyclopentyl methyl ether may be synthesized from cyclopentene. Outline a synthesis of cyclopentyl methyl ether from cyclopentene. 14. Diphenyl ether is inert to cleavage by HI or HBr. Explain. 4

5 Chapter 18 Acidic ether cleavages are typical nucleophilic substitution reactions that take place by either an S N 1 or S N 2 pathway. Diaryl ethers like diphenyl ether are inert under ordinary acidic conditions because the generation of an aryl cation is an S N 1 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. 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. 5

6 Ethers and Epoxides; Thiols and Sulfides 16. Refer to Exhibit Draw arrows showing the electron flow for this reaction on the structures provided below. 17. Refer to Exhibit 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. The carbocation generated in the first step of the S N 1 process is resonance-stabilized by the adjacent oxygen lone pairs. 6

7 Chapter 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. Basic nucleophiles like ethoxide react with epoxides in a typical S N 2-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 Show electron flow with arrows on the structures provided below for each step in the above transformation. 7

8 Ethers and Epoxides; Thiols and Sulfides 20. Refer to Exhibit The synthesis of epoxides by base treatment of halohydrins is an example of an intramolecular: a. S N 1 reaction b. hydrolysis reaction c. dehydration reaction d. Williamson ether synthesis 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

9 Chapter

10 Ethers and Epoxides; Thiols and Sulfides

11 Chapter

12 Ethers and Epoxides; Thiols and Sulfides

13 Chapter Propose a synthesis of 1,4-dioxane, starting from 1,2-dibromoethane as the only source of carbon. 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 CH 3 I B. NaOCH 3, CH 3 OH C. m-clc 6 H 4 CO 3 H D. CH 3 MgBr in ether, then H 3 O + E. warm H 2 SO 4 /H 2 O F. Hg(O 2 CCF 3 ) 2, CH 3 OH G. H 2 /Pd H. PCC, CH 2 Cl 2 I. Cl 2, H 2 O J. LiAlH 4 in ether, then H 3 O + 13

14 Ethers and Epoxides; Thiols and Sulfides 37. Complete the synthetic sequence below by drawing the structures of the reaction in the boxes provided. 14

15 Chapter Show how the ether below could be prepared from toluene and any other necessary reagents. Show all reagents and all intermediate structures. 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. 15

16 Ethers and Epoxides; Thiols and Sulfides 40. Name the compound shown below. Atoms other than carbon and hydrogen are labeled. Ethyl hexyl ether or 1-ethyoxyhexane 41. Name the following compound. Atoms other than carbon and hydrogen are labeled. o-mercaptotoluene 16

17 Chapter Predict the product of the following reaction. 43. Draw the structure of the ether that could be used to produce the following compound. 17

Chapter 22 Carbonyl Alpha-Substitution Reactions

John E. McMurry www.cengage.com/chemistry/mcmurry Chapter 22 Carbonyl Alpha-Substitution Reactions The α Position The carbon next to the carbonyl group is designated as being in the α position Electrophilic