Organic chemistry with biological applications

John E. McMurry

Chapter 8

Reactions of Alkenes and Alkynes - 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

Numerade Educator

Problem 2

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

Emilio Portillo

Emilio Portillo

Numerade Educator

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.

Niamat Khuda

Numerade Educator

Problem 4

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

Crystal Wang

Numerade Educator

Problem 5

What product would you expect from the reaction of cyclopentene with $\mathrm{Br}_{2}$ and water? Show the stereochemistry.

Rashmi Sinha

Numerade Educator

Problem 6

When an unsymmetrically substituted alkene such as propene is treated with $\mathrm{Br}_{2}$ and water, 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

Numerade Educator

Problem 7

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

Crystal Wang

Numerade Educator

Problem 8

What alkenes might the following alcohols have been prepared from?

Niamat Khuda

Numerade Educator

Problem 9

The following cycloalkene gives a mixture of two alcohols on hydroborationoxidation. Draw the structures of both, and explain the result.

Niamat Khuda

Numerade Educator

Problem 10

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

Niamat Khuda

Numerade Educator

Problem 11

What product would you expect from reaction of cis-but-2-ene with metachloroperoxybenzoic acid? Show the stereochemistry.

Niamat Khuda

Numerade Educator

Problem 12

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

Niamat Khuda

Numerade Educator

Problem 13

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

Numerade Educator

Problem 14

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

Numerade Educator

Problem 15

What product would you expect from the following reaction?

AD

Attila Dos Santos

Numerade Educator

Problem 16

What monomer units would you use to prepare the following polymers?

Lottie Adams

Numerade Educator

Problem 17

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

Numerade Educator

Problem 18

Give the structures of both 1,2 - and 1,4 -adducts resulting from reaction of 1 equivalent of $\mathrm{HCl}$ with penta-1,3-diene.

Henry R

Numerade Educator

Problem 19

Look at the possible carbocation intermediates produced during addition of HCl to penta-1,3-diene (Problem 8.18), and predict which 1,2 adduct predominates. Which 1,4 adduct predominates?

Lottie Adams

Numerade Educator

Problem 20

Give the structures of both 1,2 - and 1,4 -adducts resulting from reaction of 1 equivalent of $\mathrm{HBr}$ with the following compound:

Lottie Adams

Numerade Educator

Problem 21

Predict the product of the following Diels-Alder reaction:

Lottie Adams

Numerade Educator

Problem 22

Which of the following alkenes would you expect to be good Diels-Alder dienophiles?

Lottie Adams

Numerade Educator

Problem 23

Which of the following dienes have an $s$ -cis conformation, and which have an $s$ -trans conformation? Of the $s$ -trans dienes, which can readily rotate to $s$ -cis?

Lottie Adams

Numerade Educator

Problem 24

Predict the product of the following Diels-Alder reaction:

Lottie Adams

Numerade Educator

Problem 25

What products would you expect from the following reactions?
(a) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{C} \equiv \mathrm{CH}+2 \mathrm{Cl}_{2} \longrightarrow$ ?
(b)
(c) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{C} \equiv \mathrm{CCH}_{3}+1 \mathrm{HBr} \longrightarrow ?$

Dr. Satish Ingale

Dr. Satish Ingale

Numerade Educator

Problem 26

What product would you obtain by hydration of the following alkynes?
(a) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{C} \equiv \mathrm{CCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}$
(b)

Ian Kaigh

Numerade Educator

Problem 27

What alkynes would you start with to prepare the following ketones?

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 28

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

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 29

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.

Crystal Wang

Numerade Educator

Problem 30

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

Numerade Educator

Problem 31

Name the following alkynes, and predict the product of their reactions with (i) 1 molar equivalent of $\mathrm{H}_{2}$ in the presence of Lindlar catalyst,
(ii) 1 molar equivalent of $\mathrm{Br}_{2}$, and (iii) aqueous acid and $\mathrm{HgSO}_{4}$ catalyst:

Brittany Carnathan

Brittany Carnathan

Numerade Educator

Problem 32

Write the structures of the possible products from reaction of the following diene with 1 molar equivalent of HCl:

Ronald Prasad

Numerade Educator

Problem 33

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

Numerade Educator

Problem 34

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

Niamat Khuda

Numerade Educator

Problem 35

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

Zubair Abdulla

Numerade Educator

Problem 36

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

Niamat Khuda

Numerade Educator

Problem 37

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

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 38

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

Zubair Abdulla

Numerade Educator

Problem 39

The cis and trans isomers of but-2-ene give different dichlorocyclopropane products when treated with $\mathrm{CHCl}_{3}$ and KOH. Show the structure of each, and explain the difference.

Niamat Khuda

Numerade Educator

Problem 40

Predict the products of the following reactions, and indicate regiochemistry if relevant:

Niamat Khuda

Numerade Educator

Problem 41

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

Numerade Educator

Problem 42

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

Prashant Bana

Numerade Educator

Problem 43

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 $\mathrm{Zn}$.

Niamat Khuda

Numerade Educator

Problem 44

Show the structures of alkenes that give the following products on oxidative cleavage with $\mathrm{KMnO}_{4}$ in acidic solution:
(a) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{H}+\mathrm{CO}_{2}$
(b) $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}=\mathrm{O}+\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{H}$
(c)
(d)

Niamat Khuda

Numerade Educator

Problem 45

As we've seen, alkynes undergo many of the same addition reactions that alkenes do. What product might you expect from each of the following reactions?

Niamat Khuda

Numerade Educator

Problem 46

Predict the products of the following reactions on dec-5-yne:

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 47

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

Niamat Khuda

Numerade Educator

Problem 48

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

Numerade Educator

Problem 49

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

Crystal Wang

Numerade Educator

Problem 50

Using but-1-yne as the only organic starting material, along with any inorganic reagents needed, how would you synthesize the following compounds? More than one step may be needed.
(a) Butane
(b) 1,1,2,2 -Tetrachlorobutane
(c) 2-Bromobutane
(d) Butan-2-one $\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COCH}_{3}\right)$

Brittany Carnathan

Brittany Carnathan

Numerade Educator

Problem 51

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

Numerade Educator

Problem 52

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.

Niamat Khuda

Numerade Educator

Problem 53

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

Numerade Educator

Problem 54

Draw and name the six diene isomers of formula $\mathrm{C}_{5} \mathrm{H}_{8} .$ Which of the six are conjugated dienes?

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 55

Propose a structure for a conjugated diene that gives the same product from both 1,2 - and 1,4 -addition of $\mathrm{HCl}$.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 56

Predict the products of the following Diels-Alder reactions:

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 57

How can you account for the fact that cis-penta-1,3-diene is much less reactive than trans-penta-1,3-diene in the Diels-Alder reaction?

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 58

Would you expect a conjugated diyne such as buta-1,3-diyne to undergo Diels-Alder reaction with a dienophile? Explain.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 59

Reaction of isoprene (2-methylbuta-1,3-diene) with ethyl propenoate gives a mixture of two Diels-Alder adducts. Show the structure of each, and explain why a mixture is formed.

Dr. Satish Ingale

Dr. Satish Ingale

Numerade Educator

Problem 60

How could you use Diels-Alder reactions to prepare the following products? Show the starting diene and dienophile in each case.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 61

Acetylide anions react with aldehydes and ketones to give alcohol addition products. How might you use this reaction as part of a scheme to prepare 2 -methylbuta-1,3-diene, the starting material used in the manufacture of synthetic rubber?

Sydney Atkins

Numerade Educator

Problem 62

The oral contraceptive agent Mestranol is synthesized using a carbonyl addition reaction like that shown in Problem 8.61. Draw the structure of the ketone needed.

Tom Rutherford

Numerade Educator

Problem 63

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 64

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 65

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, $\mathbf{B}\left(\mathrm{C}_{10} \mathrm{H}_{16} \mathrm{O}_{2}\right)$.
(a) How many rings does A have?
(b) What are the structures of $\mathbf{A}$ and $\mathbf{B}$ ?
(c) Write the reactions.

Zubair Abdulla

Numerade Educator

Problem 66

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 $\mathbf{A}$ also reacts with $\mathrm{OsO}_{4}$ to give diol $\mathbf{B}$. When oxidized with $\mathrm{KMnO}_{4}$ 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.

Crystal Wang

Numerade Educator

Problem 67

When pent-4-en-1-ol is treated with aqueous $\mathrm{Br}_{2}$, a cyclic bromo ether is formed, rather than the expected bromohydrin. Propose a mechanism, using curved arrows to show electron movement.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 68

Iodine azide, IN $_{3}$, adds to alkenes by an electrophilic mechanism similar to that of bromine. If a monosubstituted alkene such as but-1-ene is used, only one product results:

Zubair Abdulla

Numerade Educator

Problem 69

The Diels-Alder reaction is reversible and can go either forward, from diene plus dienophile to a cyclohexene, or backward, from a cyclohexene to diene plus dienophile. In light of that information, propose a mechanism for the following reaction:

Ian Kaigh

Numerade Educator

Problem 70

The Diels-Alder reaction is reversible and can go either forward, from diene plus dienophile to a cyclohexene, or backward, from a cyclohexene to diene plus dienophile. In light of that information, propose a mechanism for the following reaction:

Ian Kaigh

Numerade Educator

Problem 71

Prelaureatin, a compound isolated from marine algae, is thought to be biosynthesized from laurediol by the following route. Propose a mechanism. (See Problem $8.70 .)$

Zubair Abdulla

Numerade Educator

Problem 72

As we saw in Section $8-8,1,2$ -diols undergo a cleavage reaction to give carbonyl-containing products on treatment with periodic acid, $\mathrm{HIO}_{4}$. The reaction occurs through a five-membered cyclic periodate intermediate:
When diols A and B were prepared and the rates of their reaction with $\mathrm{HIO}_{4}$ were measured, it was found that diol A cleaved approximately 1 million times faster than diol B. Make molecular models of $\mathbf{A}$ and $\mathbf{B}$ and of the potential periodate intermediates, and explain the results.

Zubair Abdulla

Numerade Educator

Problem 73

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 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 74

The following reaction takes place in high yield. Use your general knowledge of alkene electrophilic additions to propose a mechanism even though you've never seen the exact reaction before.

Anupa Sharad Medhekar

Anupa Sharad Medhekar

Numerade Educator

Problem 75

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

Numerade Educator

Problem 76

Addition of $\mathrm{BH}_{3}$ to a double bond is reversible under some conditions. Explain why hydroboration of 2 -methylpent- 2 -ene at $25^{\circ} \mathrm{C}$ followed by oxidation with alkaline $\mathrm{H}_{2} \mathrm{O}_{2}$ yields 2 -methylpentan-3-ol, but hydroboration at $160^{\circ} \mathrm{C}$ followed by oxidation yields 4 -methylpentan-1-ol.

Madeline Currie

Madeline Currie

Numerade Educator

Problem 77

Compound 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 $\mathbf{A}$ with dilute sulfuric acid, dehydration occurred and an optically inactive alkene $\mathbf{B}, \mathrm{C}_{11} \mathrm{H}_{14},$ 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

Problem 78

$\alpha$ -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 -methylheptane- 2,5 -dione.
(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