Organic Chemistry

John McMurry

Chapter 8

Alkenes: Reactions and Synthesis - all with Video Answers

Educators

Chapter Questions

Problem 1

One problem with elimination reactions is that mixtures of products are often formed. For example, treatment of 2-bromo-2-methylbutane with KOH in ethanol yields a mixture of two alkene products. What are their likely structures?

Niamat Khuda

Niamat Khuda

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Problem 2

How many alkene products, including $E, Z$ isomers, might be obtained by dehydration of 3-methyl-3-hexanol with aqueous sulfuric acid?

Emilio Portillo

Emilio Portillo

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Problem 3

What product would you expect to obtain from addition of $\mathrm{Cl}_{2}$ to 1,2 -dimethylcyclohexene? Show the stereochemistry of the product.

Nicole Krahulik

Nicole Krahulik

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Problem 4

Addition of HCI to 1,2 -dimethylcyclohexene yields a mixture of two products. Show the stereochemistry of each, and explain why a mixture is formed.

Emilio Portillo

Emilio Portillo

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Problem 5

What product would you expect from the reaction of cyclopentene with NBS and water? Show the stereochemistry.

Niamat Khuda

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Problem 6

When an unsymmetrical alkene such as propene is treated with $N$ -bromosuccinimide in aqueous dimethyl sulfoxide, the major product has the bromine atom bonded to the less highly substituted carbon atom. Is this Markovnikov or non-Markovnikov orientation? Explain.

Niamat Khuda

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Problem 7

What products would you expect from oxymercuration-demercuration of the following alkenes?
(a) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}=\mathrm{CH}_{2}$
(b) $\mathrm{CH}_{3}$ $\quad \mathrm{CH}_{3} \mathrm{C}=\mathrm{CHCH}_{2} \mathrm{CH}_{3}$

Niamat Khuda

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Problem 8

From what alkenes might the following alcohols have been prepared?

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Problem 9

Show the structures of the products you would obtain by hydroboration-oxidation of the following alkenes:

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Problem 10

What alkenes might be used to prepare the following alcohols by hydroborationoxidation?

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Problem 11

The following cycloalkene gives a mixture of two alcohols on hydroboration followed by oxidation. Draw the structures of both, and explain the result.

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Problem 12

What product would you obtain from catalytic hydrogenation of the following alkenes?

Niamat Khuda

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Problem 13

What product would you expect from reaction of cis-2-butene with meta-chloroperoxybenzoic acid? Show the stereochemistry.

Niamat Khuda

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Problem 14

How would you prepare each of the following compounds starting with an alkene?

Niamat Khuda

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Problem 15

What products would you expect from reaction of 1-methylcyclohexene with the following reagents?
(a) Aqueous acidic $\mathrm{KMnO}_{4}$
(b) $\mathrm{O}_{3},$ followed by $\mathrm{Zn}, \mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}$

Niamat Khuda

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Problem 16

Propose structures for alkenes that yield the following products on reaction with ozone followed by treatment with Zn:
(a) $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}=\mathrm{O}+\mathrm{H}_{2} \mathrm{C}=\mathrm{O}$
(b) 2 equiv $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}=\mathrm{O}$

Niamat Khuda

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Problem 17

What products would you expect from the following reactions?

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Problem 18

Show the monomer units you would use to prepare the following polymers:

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Problem 19

One of the chain-termination steps that sometimes occurs to interrupt polymerization is the following reaction between two radicals. Propose a mechanism for the reaction, using fishhook arrows to indicate electron flow.

Niamat Khuda

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Problem 20

What products are formed from acid-catalyzed hydration of racemic ( $\pm$ )-4-methyl1-hexene? What can you say about the relative amounts of the products? Is the product mixture optically active?

Anupa Sharad Medhekar

Anupa Sharad Medhekar

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Problem 21

What products are formed from hydration of 4 -methylcyclopentene? What can you say about the relative amounts of the products?

Anupa Sharad Medhekar

Anupa Sharad Medhekar

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Problem 22

Name the following alkenes, and predict the products of their reaction with (1) meta-chloroperoxybenzoic acid, (2) $\mathrm{KMnO}_{4}$ in aqueous acid, and (3) $\mathrm{O}_{3}$ followed by Zn in acetic acid:

Anupa Sharad Medhekar

Anupa Sharad Medhekar

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Problem 23

Draw the structures of alkenes that would yield the following alcohols on hydration (red $=$ O). Tell in each case whether you would use hydroborationoxidation or oxymercuration-demercuration.

Zubair Abdulla

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Problem 24

The following alkene undergoes hydroboration-oxidation to yield a single product rather than a mixture. Explain the result, and draw the product showing its stereochemistry.

Zubair Abdulla

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Problem 25

From what alkene was the following 1,2 -diol made, and what method was used, epoxide hydrolysis or $\mathrm{OsO}_{4} ?$

Anupa Sharad Medhekar

Anupa Sharad Medhekar

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Problem 26

Predict the products of the following reactions (the aromatic ring is unreactive in all cases). Indicate regiochemistry when relevant.

Niamat Khuda

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Problem 27

Suggest structures for alkenes that give the following reaction products. There may be more than one answer for some cases.

Zubair Abdulla

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Problem 28

Predict the products of the following reactions, showing both regiochemistry and stereochemistry where appropriate:

Niamat Khuda

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Problem 29

Which reaction would you expect to be faster, addition of HBr to cyclohexene or to 1-methylcyclohexene? Explain.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

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Problem 30

What product will result from hydroboration-oxidation of 1 -methylcyclopentene with deuterated borane, $\mathrm{BD}_{3} ?$ Show both the stereochemistry (spatial arrangement) and the regiochemistry (orientation) of the product.

Zubair Abdulla

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Problem 31

The cis and trans isomers of 2-butene give different cyclopropane products in the Simmons-Smith reaction. Show the structures of both, and explain the difference.

Niamat Khuda

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Problem 32

Predict the products of the following reactions. Don't worry about the size of the molecule; concentrate on the functional groups.

Niamat Khuda

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Problem 33

Reaction of 2 -methylpropene with $\mathrm{CH}_{3} \mathrm{OH}$ in the presence of $\mathrm{H}_{2} \mathrm{SO}_{4}$ catalyst yields methyl tert-butyl ether, $\mathrm{CH}_{3} \mathrm{OC}\left(\mathrm{CH}_{3}\right)_{3},$ by a mechanism analogous to that of acid-catalyzed alkene hydration. Write the mechanism, using curved arrows for each step.

Niamat Khuda

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Problem 34

Addition of HCl to 1 -methoxycyclohexene yields 1 -chloro-1-methoxycyclohexane as the sole product. Use resonance structures of the carbocation intermediate to explain why none of the other regioisomer is formed.

Niamat Khuda

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Problem 35

How would you carry out the following transformations? Tell the reagents you would use in each case.

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Problem 36

Draw the structure of an alkene that yields only acetone, $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}=\mathrm{O},$ on ozonolysis followed by treatment with Zn.

Niamat Khuda

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Problem 37

Show the structures of alkenes that give the following products on oxidative cleavage with $\mathrm{KMnO}_{4}$ in acidic solution:

Niamat Khuda

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Problem 38

In planning the synthesis of one compound from another, it's just as important to know what not to do as to know what to do. The following reactions all have serious drawbacks to them. Explain the potential problems of each.

Zubair Abdulla

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Problem 39

Which of the following alcohols could not be made selectively by hydroborationoxidation of an alkene? Explain.

Zubair Abdulla

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Problem 40

Plexiglas, a clear plastic used to make many molded articles, is made by polymerization of methyl methacrylate. Draw a representative segment of Plexiglas.

Niamat Khuda

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Problem 41

Poly(vinyl pyrrolidone), prepared from $N$ -vinylpyrrolidone, is used both in cosmetics and as a synthetic blood substitute. Draw a representative segment of the polymer.

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Problem 42

When a single alkene monomer, such as ethylene, is polymerized, the product is a homopolymer. If a mixture of two alkene monomers is polymerized, however, a copolymer often results. The following structure represents a segment of a copolymer called Saran. What two monomers were copolymerized to make Saran?

Niamat Khuda

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Problem 43

Compound A has the formula $\mathrm{C}_{10} \mathrm{H}_{16}$. On catalytic hydrogenation over palladium, it reacts with only 1 molar equivalent of $\mathrm{H}_{2}$. Compound A also undergoes reaction with ozone, followed by zinc treatment, to yield a symmetrical diketone, $\mathbf{B}\left(\mathbf{C}_{10} \mathrm{H}_{16} \mathrm{O}_{2}\right)$
(a) How many rings does A have?
(b) What are the structures of A and B?
(c) Write the reactions.

Zubair Abdulla

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Problem 44

An unknown hydrocarbon A with the formula $\mathrm{C}_{6} \mathrm{H}_{12}$ reacts with 1 molar equivalent of $\mathrm{H}_{2}$ over a palladium catalyst. Hydrocarbon $\mathrm{A}$ also reacts with OsO_ to give diol B. When oxidized with KMnO_in acidic solution, A gives two fragments. One fragment is propanoic acid, $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{H},$ and the other fragment is ketone $\mathbf{C .}$ What are the structures of $\mathbf{A}, \mathbf{B},$ and $\mathbf{C} ?$ Write all reactions, and show your reasoning.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 45

Using an oxidative cleavage reaction, explain how you would distinguish between the following two isomeric dienes:

Niamat Khuda

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Problem 46

Compound $A, C_{10} H_{18} O,$ undergoes reaction with dilute $H_{2} S O_{4}$ at $50^{\circ} \mathrm{C}$ to yield a mixture of two alkenes, $\mathrm{C}_{10} \mathrm{H}_{16}$. The major alkene product, $\mathrm{B},$ gives only cyclopentanone after ozone treatment followed by reduction with zinc in acetic acid. Identify A and B, and write the reactions.

Niamat Khuda

Numerade Educator

Problem 47

Iodine azide, IN $_{3}$, adds to alkenes by an electrophilic mechanism similar to that of bromine. If a monosubstituted alkene such as 1 -butene is used, only one product results:
$$\mathrm{CH}_{3} \mathrm{cH}_{2} \mathrm{CH}=\mathrm{CH}_{2}+\mathrm{I}-\mathrm{N}=\mathrm{N}=\mathrm{N} \longrightarrow \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHCH}_{2} \mathrm{I}$$
(a) Add lone-pair electrons to the structure shown for IN $_{3}$, and draw a second resonance form for the molecule.
(b) Calculate formal charges for the atoms in both resonance structures you drew for IN $_{3}$ in part (a).
(c) In light of the result observed when IN $_{3}$ adds to 1 -butene, what is the polarity of the $\mathrm{I}-\mathrm{N}_{3}$ bond? Propose a mechanism for the reaction using curved arrows to show the electron flow in each step.

Zubair Abdulla

Numerade Educator

Problem 48

10-Bromo- $\alpha$ -chamigrene, a compound isolated from marine algae, is thought to be biosynthesized from $\gamma$ -bisabolene by the following route:
Draw the structures of the intermediate bromonium and cyclic carbocation, and propose mechanisms for all three steps.

Zubair Abdulla

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Problem 49

Draw the structure of a hydrocarbon that absorbs 2 molar equivalents of $\mathrm{H}_{2}$ on catalytic hydrogenation and gives only butanedial on ozonolysis.

Niamat Khuda

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Problem 50

Simmons-Smith reaction of cyclohexene with diiodomethane gives a single cyclopropane product, but the analogous reaction of cyclohexene with 1,1-diiodoethane gives (in low yield) a mixture of two isomeric methylcyclopropane products. What are the two products, and how do they differ?

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 51

The sex attractant of the common housefly is a hydrocarbon with the formula $\mathrm{C}_{23} \mathrm{H}_{46} .$ On treatment with aqueous acidic $\mathrm{KMnO}_{4},$ two products are obtained, $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{12} \mathrm{CO}_{2} \mathrm{H}$ and $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{7} \mathrm{CO}_{2} \mathrm{H} .$ Propose a structure.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 52

Compound A has the formula $\mathrm{C}_{8} \mathrm{H}_{8} .$ It reacts rapidly with $\mathrm{KMnO}_{4}$ to give
$\mathrm{CO}_{2}$ and a carboxylic acid, $\mathrm{B}\left(\mathrm{C}_{7} \mathrm{H}_{6} \mathrm{O}_{2}\right),$ but reacts with only 1 molar equivalent of $\mathrm{H}_{2}$ on catalytic hydrogenation over a palladium catalyst. On hydrogenation under conditions that reduce aromatic rings, 4 equivalents of $\mathrm{H}_{2}$ are taken up and hydrocarbon $\mathbf{C}\left(\mathrm{C}_{8} \mathrm{H}_{16}\right)$ is produced. What are the structures of $\mathrm{A}, \mathrm{B},$ and $\mathrm{C} ?$ Write the reactions.

Niamat Khuda

Numerade Educator

Problem 53

Isolated from marine algae, prelaureatin is thought to be biosynthesized from laurediol by the following route. Propose a mechanism.

Zubair Abdulla

Numerade Educator

Problem 54

How would you distinguish between the following pairs of compounds using simple chemical tests? Tell what you would do and what you would see.
(a) Cyclopentene and cyclopentane
(b) 2 -Hexene and benzene

Niamat Khuda

Numerade Educator

Problem 55

Dichlorocarbene can be generated by heating sodium trichloroacetate. Propose a mechanism for the reaction, and use curved arrows to indicate the movement of electrons in each step. What relationship does your mechanism bear to the base-induced elimination of HCl from chloroform?

Zubair Abdulla

Numerade Educator

Problem 56

$\alpha$ -Terpinene, $\mathrm{C}_{10} \mathrm{H}_{16},$ is a pleasant-smelling hydrocarbon that has been isolated from oil of marjoram. On hydrogenation over a palladium catalyst, $\alpha$ -terpinene reacts with 2 molar equivalents of $\mathrm{H}_{2}$ to yield a hydrocarbon, $\mathrm{C}_{10} \mathrm{H}_{20} .$ On ozonolysis, followed by reduction with zinc and acetic acid, $\alpha$ -terpinene yields two products, glyoxal and 6 -methyl- 2,5 -heptanedione.
(a) How many degrees of unsaturation does $\alpha$ -terpinene have?
(b) How many double bonds and how many rings does it have?
(c) Propose a structure for $\alpha$ -terpinene.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 57

Evidence that cleavage of 1,2 -diols by HIO $_{4}$ occurs through a five-membered cyclic periodate intermediate is based on kinetic data-the measurement of reaction rates. When diols A and B were prepared and the rates of their reaction with HIO_ were measured, it was found that diol A cleaved approximately 1 million times faster than diol B. Make molecular models of A and B and of potential cyclic periodate intermediates, and then explain the kinetic results.

Zubair Abdulla

Numerade Educator

Problem 58

Reaction of HBr with 3-methylcyclohexene yields a mixture of four products: cis- and trans-1-bromo-3-methylcyclohexane and cis- and trans-1-bromo2-methylcyclohexane. The analogous reaction of HBr with 3-bromocyclohexene yields trans-1,2-dibromocyclohexane as the sole product. Draw structures of the possible intermediates, and then explain why only a single product is formed in the reaction of HBr with 3-bromocyclohexene.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 59

Reaction of cyclohexene with mercury(II) acetate in $\mathrm{CH}_{3} \mathrm{OH}$ rather than $\mathrm{H}_{2} \mathrm{O}$ followed by treatment with $\mathrm{NaBH}_{4},$ yields cyclohexyl methyl ether rather than cyclohexanol. Suggest a mechanism.

Niamat Khuda

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Problem 60

Use your general knowledge of alkene chemistry to suggest a mechanism for the following reaction.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 61

Treatment of 4 -penten-1-ol with aqueous $\mathrm{Br}_{2}$ yields a cyclic bromo ether rather than the expected bromohydrin, Suggest a mechanism, using curved arrows to show electron movement.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 62

Hydroboration of 2-methyl-2-pentene at $25^{\circ} \mathrm{C}$ followed by oxidation with alkaline $\mathrm{H}_{2} \mathrm{O}_{2}$ yields 2 -methyl-3-pentanol, but hydroboration at $160^{\circ} \mathrm{C}$ followed by oxidation yields 4 -methyl-1-pentanol. Suggest a mechanism.

Zubair Abdulla

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Problem 63

We'll see in the next chapter that alkynes undergo many of the same reactions that alkenes do. What product might you expect from each of the following reactions?

Niamat Khuda

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Problem 64

Hydroxylation of cis-2-butene with OsO_y yields a different product than hydroxylation of trans-2-butene. Draw the structure, show the stereochemistry of each product, and explain the difference between them.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 65

Compound $\mathbf{A}, \mathrm{C}_{11} \mathrm{H}_{16} \mathrm{O},$ was found to be an optically active alcohol. Despite its apparent unsaturation, no hydrogen was absorbed on catalytic reduction over a palladium catalyst. On treatment of A with dilute sulfuric acid, dehydration occurred and an optically inactive alkene $\mathbf{B}, \mathbf{C}_{11} \mathrm{H}_{14},$ was produced as the major product. Alkene $\mathbf{B},$ on ozonolysis, gave two products. One product was identified as propanal, $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CHO} .$ Compound $\mathbf{C},$ the other product, was shown to be a ketone, $\mathrm{C}_{8} \mathrm{H}_{8} \mathrm{O}$. How many degrees of unsaturation does A have? Write the reactions, and identify $\mathbf{A}, \mathbf{B},$ and $\mathbf{C} .$

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator