Chapter 9 HOMEWORK SHORT ANSWER. Drawing Instructions: Draw structures corresponding to each of the given names. 1. Draw: ethynylcyclopropane ANS:

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1 Chapter 9 HOMEWORK SHORT ANSWER Drawing Instructions: Draw structures corresponding to each of the given names. 1. Draw: ethynylcyclopropane 2. Draw: 3,10-dimethyl-6-sec-butylcyclodecyne 3. Draw: 4-bromo-3,3-dimethyl-1-hexen-5-yne 4. Draw: acetylene IUPAC Naming Instructions: Provide proper IUPAC names. 5. Name: 4-methyl-2-heptyne 1

2 Alkynes: An Introduction to Organic Synthesis 6. Name: 1-ethynyl-2-methylcyclopentane Exhibit 9-1 The compound below has been isolated from the safflower plant. Consider its structure to answer the following question(s). 7. Refer to Exhibit 9-1. What is the molecular formula for this natural product? C 13 H Refer to Exhibit 9-1. What is the degree of unsaturation for this compound? We can arrive at the degree of unsaturation for a structure in two ways. Since we know that the degree of unsaturation is the number of rings and/or multiple bonds in a compound, we can simply count them. There are three double bonds (3 degrees) and three triple bonds (six degrees), so the degree of unsaturation is 9. We can verify this by using the molecular formula, C 13 H 10, to calculate a degree of unsaturation. The saturated 13-carbon compound should have the base formula C 13 H 28, so (28 10) 2 = 18 2 = 9. 2

3 Chapter 9 9. Refer to Exhibit 9-1. Assign E or Z configuration to each of the double bonds in the compound. 10. Refer to Exhibit 9-1. Provide the name for this unusual natural product. (3E, 11E)-1,3,11-tridecatrien-5,7,9-triyne or (3E,11E)-trideca-1,3,11-trien-5,7,9-triyne Exhibit 9-2 To answer the following question(s), consider the information below: The heat of hydrogenation of 1,4-pentadiene is kj/mol. The heat of hydrogenation of 1- pentyne is approximately kj/mol. 11. Refer to Exhibit 9-2. Which structure is more stable, 1,4-pentadiene or 1-pentyne? Briefly explain your answer. 1,4-pentadiene The heat of hydration is the amount of energy released when hydrogen adds to the multiple carbon-to-carbon bonds in a compound and converts it to the corresponding saturated compound. The larger the value, the more energy that is released during the hydrogenation. Both of these substances, end up as pentane upon complete hydrogenation. That is, they end up at the same final energy level. Less energy is released by 1,4-pentadiene, therefore, this reactant has less energy to start with or is more stable than 1-pentyne. 3

4 Alkynes: An Introduction to Organic Synthesis 12. Refer to Exhibit 9-2. Show the energy differences between the hydrogenation of 1,4- pentadiene and 1-pentyne on a reaction energy diagram. Exhibit 9-3 Consider an unknown with the molecular formula C 4 H Refer to Exhibit 9-3. How many degrees of unsaturation are present? A saturated four carbon compound has the formula C 4 H 10. Therefore this compound has (10 6) 2 = 2 degrees of unsaturation. 14. Refer to Exhibit 9-3. Draw six of the nine possible structures with this formula. 4

5 Chapter 9 Exhibit 9-4 Predict the product of each reaction below. Be sure to indicate stereochemistry when appropriate

6 Alkynes: An Introduction to Organic Synthesis Exhibit 9-5 To answer the following question(s) consider this reaction: 22. Refer to Exhibit 8-5. On the structures provided, draw arrows showing the electron flow for the reaction mechanism for the electrophilic addition of hydrogen bromide to 1-hexyne. 6

7 Chapter Refer to Exhibit 8-5. The key intermediate in the electrophilic addition reaction shown above is called: a. an acetylenic carbocation b. a vinylic bromide c. a secondary carbocation d. a vinylic carbocation d Exhibit 9-6 Select the best reagent or sequence of reagents from the list provided which would best accomplish each transformation below. Place the letter corresponding to the reagent(s) in the blank to the left of each reaction. Each transformation requires only one answer. a. H 2 SO 4, H 2 O, HgSO 4 e. 1. Br 2, CCl 4 b. H 2, Lindlar 2. 2 NaNH 2, NH 3 c. 1. BH 3, THF f. 1. HCl 2. H 2 O 2 2. NaNH 2, NH 3 d. 1. NaNH 2, NH 3 g. Li/NH 3 2. CH 3 CH 2 I h. 1. NaNH 2, NH 3 2. CH 3 CH 2 CH 2 I 24. g 7

8 Alkynes: An Introduction to Organic Synthesis 25. a 26. h 27. e Exhibit 9-7 Show all reagents and intermediates necessary to carry out the following conversions

9 Chapter Exhibit 9-8 Using acetylene and any alkyl halides as starting materials, synthesize the following compounds. More than one step may be required. Show all reagents and all intermediate compounds in your synthetic scheme

10 Alkynes: An Introduction to Organic Synthesis

11 Chapter

CHEM 203 Exam 1. KEY Name Multiple Choice Identify the letter of the choice that best completes the statement or answers the question.

CHEM 203 Exam 1. KEY Name Multiple Choice Identify the letter of the choice that best completes the statement or answers the question. CHEM 203 Exam 1 KEY Name Multiple Choice Identify the letter of the choice that best completes the statement or answers the question. _D C 1. Which of the following elements is a large percentage of both