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 $\mathrm{KOH}$ in ethanol yields a mixture of two alkene products. What are their likely structures?

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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?figure cant copy

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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.

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Problem 4

Addition of $\mathrm{HCl}$ to 1,2-dimethylcyclohexene yields a mixture of two products. Show the stereochemistry of each, and explain why a mixture is formed.

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Problem 5

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

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Problem 6

When an unsymmetrical alkene such as propene is treated with $\mathrm{N}$-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? (Section 7.8) Explain.

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Problem 7

What products would you expect from oxymercuration-demercuration of the following alkenes?
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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 hydroboration–oxidation?
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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?
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Problem 13

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

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Problem 14

Starting with an alkene, how would you prepare each of the following compounds?
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Problem 14

Starting with an alkene, how would you prepare each of the following compounds?

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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 $\mathrm{Zn}, \mathrm{CH}_3 \mathrm{CO}_2 \mathrm{H}$

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Problem 16

Propose structures for alkenes that yield the following products on reaction with ozone followed by treatment with $\mathrm{Zn}$ :
(a) $\left(\mathrm{CH}_3\right)_2 \mathrm{C}=\mathrm{O}+\mathrm{H}_2 \mathrm{C}=\mathrm{O}$
(b) 2 equiv $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}=\mathrm{O}$

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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.
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Problem 20

What products are formed from acid-catalyzed hydration of racemic $( \pm)-4$-methyl-1-hexene? What can you say about the relative amounts of the products? Is the product mixture optically active?

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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, (3) $\mathrm{O}_3$, followed by $\mathrm{Zn}$ in acetic acid:
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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 hydroboration–oxidation or oxymercuration–demercuration.
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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.
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Problem 25

From what alkene was the following 1,2-diol made, and what method was used, epoxide hydrolysis
or OsO4?
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Problem 26

Predict the products for the following reactions, showing the complete mechanism and appropriate
stereochemistry:
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Problem 27

Draw the structures of the organoboranes formed when borane reacts with the following alkenes,
including the regiochemistry and stereochemistry as appropriate. Propose a mechanism for each
reaction.
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Crystal Wang

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Problem 28

meta-Chlorobenzoic acid is not the only peroxyacid capable of epoxide formation. For each reaction
below, predict the products and show the mechanism.
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Problem 29

Give the mechanism and products for the following acid-catalyzed epoxide-opening reactions,
including appropriate stereochemistry.
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Problem 30

Which of the reactions below would result in a product mixture that would rotate plane-polarized
light?
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Problem 31

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.

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Problem 32

Iodine azide, $\mathrm{IN}_3$, 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:

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Problem 33

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

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Problem 34

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

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Problem 35

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?
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Problem 36

Reaction of cyclohexene with mercury(II) acetate in CH3OH rather than H2O, followed by treatment
with NaBH4, yields cyclohexyl methyl ether rather than cyclohexanol. Suggest a mechanism.
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Problem 37

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

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Problem 38

Treatment of 4-penten-1-ol with aqueous Br2 yields a cyclic bromo ether rather than the expected
bromohydrin. Suggest a mechanism, using curved arrows to show electron movement.
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Anupa Sharad Medhekar

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Problem 39

Hydroboration of 2-methyl-2-pentene at 25 °C, followed by oxidation with alkaline H2O2, yields
2-methyl-3-pentanol, but hydroboration at 160 °C followed by oxidation yields
4-methyl-1-pentanol. Suggest a mechanism.
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Problem 40

Predict the products of the following reactions (the aromatic ring is unreactive in all cases). Indicate
regiochemistry when relevant.
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Problem 41

Suggest structures for alkenes that give the following reaction products. There may be more than
one answer for some cases.
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Problem 42

Predict the products of the following reactions, showing both regiochemistry and stereochemistry
where appropriate:
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Problem 43

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

Anupa Sharad Medhekar

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Problem 44

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.

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Problem 45

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.

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Problem 46

Predict the products of the following reactions. Don’t worry about the size of the molecule;
concentrate on the functional groups.
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Problem 47

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

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Problem 48

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

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Problem 49

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 $\mathrm{Zn}$.

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Problem 50

Show the structures of alkenes that give the following products on oxidative cleavage with $\mathrm{KMnO}_4$ in acidic solution:
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Problem 51

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.
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Problem 52

Which of the following alcohols could not be made selectively by hydroboration–oxidation of an
alkene? Explain.
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Problem 53

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

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Problem 54

Poly(vinyl pyrrolidone), prepared from N-vinylpyrrolidone, is used both in cosmetics and as a
component of a synthetic substitute for blood. Draw a representative segment of the polymer.
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Problem 55

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?
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Problem 56

Compound $\mathrm{A}$ 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 $\mathbf{A}$ also undergoes reaction with ozone, followed by zinc treatment, to yield a symmetrical diketone, $\mathbf{B}\left(\mathrm{C}_{10} \mathrm{H}_{16} \mathrm{O}_2\right)$.
(a) How many rings does $\mathbf{A}$ have? (b) What are the structures of $\mathbf{A}$ and $\mathbf{B}$ ?
(c) Write the reactions.

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Problem 57

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 A also reacts with $\mathrm{OsO}_4$ to give diol B. When oxidized with $\mathrm{KMnO}_4$
in acidic solution, $\mathbf{A}$ 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.

Anupa Sharad Medhekar

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Problem 58

Using an oxidative cleavage reaction, explain how you would distinguish between the following two
isomeric dienes:
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Problem 59

Compound A, C10H18O, undergoes reaction with dilute H2SO4 at 50 °C to yield a mixture of two
alkenes, C10H16. The major alkene product, B, gives only cyclopentanone after ozone treatment
followed by reduction with zinc in acetic acid. Identify A and B, and write the reactions.
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Problem 60

Draw the structure of a hydrocarbon that absorbs 2 molar equivalents of H2 on catalytic
hydrogenation and gives only butanedial on ozonolysis.
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Problem 61

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?

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Problem 62

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

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Problem 63

Compound $\mathbf{A}$ 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, $\mathbf{B}\left(\mathrm{C}_7 \mathrm{H}_6 \mathrm{O}_2\right)$, but reacts with only $1 \mathrm{molar}$ 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 $\mathbf{A}, \mathbf{B}$, and $\mathbf{C}$ ? Write the reactions.

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Problem 64

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
$\alpha$-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.
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Niamat Khuda

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Problem 65

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
$\alpha$-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.
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(a) How many degrees of unsaturation does ?-terpinene have?
(b) How many double bonds and how many rings does it have?
(c) Propose a structure for ?-terpinene.

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Problem 66

Evidence that cleavage of 1,2-diols by HIO4 occurs through a five-membered cyclic periodate
intermediate is based on the measurement of reaction rates. When diols A and B were prepared and
the rates of their reaction with HIO4 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 results.
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Zubair Abdulla

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Problem 67

Reaction of HBr with 3-methylcyclohexene yields a mixture of four products: cis- and
trans-1-bromo-3-methylcyclohexane and cis- and trans-1-bromo-2-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 this reaction.
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Anupa Sharad Medhekar

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Problem 68

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?
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Niamat Khuda

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Problem 69

Hydroxylation of cis-2-butene with $\mathrm{OsO}_4$ 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

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Problem 70

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 B, $\mathrm{C}_{11} \mathrm{H}_{14}$, was 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 $\mathbf{A}$ have? Write the reactions, and identify $\mathbf{A}, \mathbf{B}$, and c.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

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