Organic Chemistry

262 CHAPTER 6 Reactions of Alkynes • Introduction to Multistep Synthesis

36. Which of the following pairs are keto–enol tautomers?

a. d.

b. e.

c.

37. Using ethyne as the starting material, how can the following compounds be prepared?

a. c. e.

b. d. f.

38. Give the stereoisomers obtained from the reaction of 2-butyne with the following reagents:
    a. 1. catalyst 2.
    b. 1. 2.
    c. 1. 2.


39. Draw the keto tautomer for each of the following:

a. b. c. d.

40. Show how each of the following compounds could be prepared using the given starting material, any necessary inorganic reagents,
    and any necessary organic compound that has no more than four carbon atoms:

a. d.

b. e.

c. f.

41. Dr. Polly Meher was planning to synthesize 3-octyne by adding
    1-bromobutane to the product obtained from the reaction of 1-butyne with sodium amide. Unfortunately, however, she had
    forgotten to order 1-butyne. How else can she prepare 3-octyne?


42. a. Explain why a single pure product is obtained from hydroboration–oxidation of 2-butyne, whereas two products are obtained
    from hydroboration–oxidation of 2-pentyne.
    b. Name two other internal alkynes that will yield only one product on hydroboration–oxidation.


43. Give the configurations of the products obtained from the following reactions:


44. In Section 6.4 it was stated that hyperconjugation is less effective in stabilizing the charge on a vinylic cation than the charge on an
    alkyl cation. Why do you think this is so?

CH 3 CH 2 C CCH 2 CH 3

CH 3 CH 2 C CCH 2 CH 3

1. Na, NH 3 (liq)


2. D 2 , Pd/C


3. H 2 /Lindlar catalyst


4. D 2 , Pd/C

a.

b.

C CCH 3

H H

CH 3

CC

OH

HC CH CH 3 CH 2 CH 2 CHCH 3

O

C CH CCH 3

Br

HC CH CH 3 CH 2 CHCH 3

O

C CH CH 2 CH

O

HC CH CH 3 CH 2 CH 2 CH 2 CCH 3

CH 2 OH CHOH

OH

CCH 3 CH 3 CH 2 CH 2 C

OH

CH 3 CH

Cl 2 >CH 2 Cl 2 Br 2 >CH 2 Cl 2

Na>NH 3 (liq) Br 2 >CH 2 Cl 2

H 2 >Lindlar Br 2 >CH 2 Cl 2

Br

CH 3 CH 2 CHCH 2 Br

O

CH 3 CCH 3

O

CH 3 CH

CH 3 CH 2 CH CHOH and CH 3 CH 2 CH 2 CH

O

CH 2

OH O

CH 3 CH 2 CH 2 CCHand 3 CH 2 CH 2 CCH 3

OH O

CH 3 CHCH 3 and CH 3 CCH 3

CH 3 CH 2 CH 2 CH CHOH and CH 3 CH 2 CH 2 CCH 3

O O

CH 3 CH 2 CH CHCH 2 OH and CH 3 CH 2 CH 2 CH 2 CH

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