Additional Problems 9

David Tully

Additional Problems

Problem 9-14

Name the following alkynes, and predict the products of their reaction with (1) H₂ in the presence of a Lindlar catalyst and (2) H₃O⁺ in the presence of HgSO₄:

(a)

(b)

Problem 9-15

From what alkyne might each of the following substances have been made? (Green = Cl.)

(a)

(b)

Problem 9-16

How would you prepare the following substances, starting from any compounds having four carbons or fewer?

(a)

(b)

Problem 9-17

The following cycloalkyne is too unstable to exist. Explain.

Mechanism Problems

Problem 9-18

Assuming that halogens add to alkynes in the same manner as they add to alkenes, propose a mechanism for and predict the product(s) of the reaction of phenylpropyne with Br₂.

Problem 9-19

Assuming that strong acids add to alkynes in the same manner as they add to alkenes, propose a mechanism for each of the following reactions.

(a)

(b)

(c)

Problem 9-20

The mercury-catalyzed hydration of alkynes involves the formation of an organomercury enol intermediate. Draw the electron-pushing mechanism to show how each of the following intermediates is formed.

(a)

(b)

(c)

Problem 9-21

The final step in the hydration of an alkyne under acidic conditions is the tautomerization of an enol intermediate to give the corresponding ketone. The mechanism involves a protonation followed by a deprotonation. Show the mechanism for each of the following tautomerizations.

(a)

(b)

(c)

Problem 9-22

Predict the product(s) and show the complete electron-pushing mechanism for each of the following dissolving metal reductions.

(a)

(b)

(c)

Problem 9-23

Identify the mechanisms for the following reactions as polar, radical, or both.

(a)

(b)

(c)

Problem 9-24

Predict the product and provide the complete electron-pushing mechanism for the following two-step synthetic processes.

(a)

(b)

(c)

Problem 9-25

Reaction of acetone with D₃O⁺ yields hexadeuterioacetone. That is, all the hydrogens in acetone are exchanged for deuterium. Review the mechanism of mercuric-ion-catalyzed alkyne hydration, and then propose a mechanism for this deuterium incorporation.

Naming Alkynes

Problem 9-26

Give IUPAC names for the following compounds:

(a)

(b)

(c)

(d)

(e)

(f)

Problem 9-27

Draw structures corresponding to the following names:

(a) 3,3-Dimethyl-4-octyne

(b) 3-Ethyl-5-methyl-1,6,8-decatriyne

(c) 2,2,5,5-Tetramethyl-3-hexyne

(d) 3,4-Dimethylcyclodecyne

(e) 3,5-Heptadien-1-yne

(f) 3-Chloro-4,4-dimethyl-1-nonen-6-yne

(g) 3-sec–Butyl-1-heptyne

(h) 5-tert-Butyl-2-methyl-3-octyne

Problem 9-28

The following two hydrocarbons have been isolated from various plants in the sunflower family. Name them according to IUPAC rules.

(a) CH₃CH=CHC≡CC≡CCH=CHCH=CHCH=CH₂ (all trans)

(b) CH₃C≡CC≡CC≡CC≡CC≡CCH=CH₂

Reactions of Alkynes

Problem 9-29

Terminal alkynes react with Br₂ and water to yield bromo ketones. For example:

Propose a mechanism for the reaction. To what reaction of alkenes is the process analogous?

Problem 9-30

Predict the products of the following reactions:

Problem 9-31

Predict the products from reaction of 1-hexyne with the following reagents:

(a) 1 equiv HBr

(b) 1 equiv Cl₂

(c) H₂, Lindlar catalyst

(d) NaNH₂ in NH₃, then CH₃Br

(e) H₂O, H₂SO₄, HgSO₄

(f) 2 equiv HCl

Problem 9-32

Predict the products from reaction of 5-decyne with the following reagents:

(a) H₂, Lindlar catalyst

(b) Li in NH₃

(c) 1 equiv Br₂

(d) BH₃ in THF, then H₂O₂, OH⁻

(e) H₂O, H₂SO₄, HgSO₄

(f) Excess H₂, Pd/C catalyst

Problem 9-33

Predict the products from reaction of 2-hexyne with the following reagents:

(a) 2 equiv Br₂

(b) 1 equiv HBr

(c) Excess HBr

(d) Li in NH₃

(e) H₂O, H₂SO₄, HgSO₄

Problem 9-34

Propose structures for hydrocarbons that give the following products on oxidative cleavage by KMnO₄ or O₃:

(a)

(b)

(c)

(d)

(e)

Problem 9-35

Identify the reagents a–c in the following scheme:

Organic Synthesis

Problem 9-36

How would you carry out the following multistep conversions? More than one step may be needed in some instances.

Problem 9-37

How would you carry out the following reactions?

(a)

(b)

(c)

(d)

(e)

(f)

Problem 9-38

Each of the following syntheses requires more than one step. How would you carry them out?

(a)

(b)

Problem 9-39

How would you carry out the following multistep transformation?

Problem 9-40

How would you carry out the following multistep conversions?

Problem 9-41

Synthesize the following compounds using 1-butyne as the only source of carbon, along with any inorganic reagents you need. More than one step may be needed.

(a) 1,1,2,2-Tetrachlorobutane

(b) 1,1-Dichloro-2-ethylcyclopropane

Problem 9-42

How would you synthesize the following compounds from acetylene and any alkyl halides with four or fewer carbons? More than one step may be needed.

(a)

(b)

(c)

(d)

(e)

Problem 9-43

How would you carry out the following reactions to introduce deuterium into organic molecules?

(a)

(b)

(c)

(d)

Problem 9-44

How would you prepare cyclodecyne starting from acetylene and any required alkyl halide?

Problem 9-45

The sex attractant given off by the common housefly is an alkene named muscalure. Propose a synthesis of muscalure starting from acetylene and any alkyl halides needed. What is the IUPAC name for muscalure?

General Problems

Problem 9-46

A hydrocarbon of unknown structure has the formula C₈H₁₀. On catalytic hydrogenation over the Lindlar catalyst, 1 equivalent of H₂ is absorbed. On hydrogenation over a palladium catalyst, 3 equivalents of H₂ are absorbed.

(a) How many degrees of unsaturation are present in the unknown structure?

(b) How many triple bonds are present?

(c) How many double bonds are present?

(d) How many rings are present?

(e) Draw a structure that fits the data.

Problem 9-47

Compound A (C₉H₁₂) absorbed 3 equivalents of H₂ on catalytic reduction over a palladium catalyst to give B (C₉H₁₈). On ozonolysis, compound A gave, among other things, a ketone that was identified as cyclohexanone. On treatment with NaNH₂ in NH₃, followed by addition of iodomethane, compound A gave a new hydrocarbon, C (C₁₀H₁₄). What are the structures of A, B, and C?

Problem 9-48

Hydrocarbon A has the formula C₁₂H₈. It absorbs 8 equivalents of H₂ on catalytic reduction over a palladium catalyst. On ozonolysis, only two products are formed: oxalic acid (HO₂CCO₂H) and succinic acid (HO₂CCH₂CH₂CO₂H). Write the reactions, and propose a structure for A.

Problem 9-49

Occasionally, a chemist might need to invert the stereochemistry of an alkene—that is, to convert a cis alkene to a trans alkene, or vice versa. There is no one-step method for doing an alkene inversion, but the transformation can be carried out by combining several reactions in the proper sequence. How would you carry out the following reactions?

(a)

(b)

Problem 9-50

Organometallic reagents such as sodium acetylide undergo an addition reaction with ketones, giving alcohols:

How might you use this reaction to prepare 2-methyl-1,3-butadiene, the starting material used in the manufacture of synthetic rubber?

Problem 9-51

The oral contraceptive agent Mestranol is synthesized using a carbonyl addition reaction like that shown in Problem 9-50. Draw the structure of the ketone needed.

Problem 9-52

1-Octen-3-ol, a potent mosquito attractant commonly used in mosquito traps, can be prepared in two steps from hexanal, CH₃CH₂CH₂CH₂CH₂CHO. The first step is an acetylide- addition reaction like that described in Problem 9-50. What is the structure of the product from the first step, and how can it be converted into 1-octen-3-ol?

Problem 9-53

Erythrogenic acid, C₁₈H₂₆O₂, is an acetylenic fatty acid that turns a vivid red on exposure to light. On catalytic hydrogenation over a palladium catalyst, 5 equivalents of H₂ are absorbed, and stearic acid, CH₃(CH₂)₁₆CO₂H, is produced. Ozonolysis of erythrogenic acid gives four products: formaldehyde, CH₂O; oxalic acid, HO₂CCO₂H; azelaic acid, HO₂C(CH₂)₇CO₂H; and the aldehyde acid OHC(CH₂)₄CO₂H. Draw two possible structures for erythrogenic acid, and suggest a way to tell them apart by carrying out some simple reactions.

Problem 9-54

Hydrocarbon A has the formula C₉H₁₂ and absorbs 3 equivalents of H₂ to yield B, C₉H1₈, when hydrogenated over a Pd/C catalyst. On treatment of A with aqueous H₂SO₄ in the presence of mercury(II), two isomeric ketones, C and D, are produced. Oxidation of A with KMnO₄ gives a mixture of acetic acid (CH₃CO₂H) and the tricarboxylic acid E. Propose structures for compounds A–D, and write the reactions.

Problem 9-55

A cumulene is a compound with three adjacent double bonds. Draw an orbital picture of a cumulene. What kind of hybridization do the two central carbon atoms have? What is the geometric relationship of the substituents on one end to the substituents on the other end? What kind of isomerism is possible? Make a model to help see the answer.