Organic chemistry with biological applications

John E. McMurry

Chapter 7

Alkenes and Alkynes - all with Video Answers

Educators

Chapter Questions

Problem 1

Calculate the degree of unsaturation in each of the following formulas, and then draw as many structures as you can for each:
(a) $\mathrm{C}_{4} \mathrm{H}_{8}$
(b) $\mathrm{C}_{4} \mathrm{H}_{6}$
(c) $\mathrm{C}_{3} \mathrm{H}_{4}$

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 2

Calculate the degree of unsaturation in each of the following formulas:
(a) $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{~N}$
(b) $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NO}_{2}$
(c) $\mathrm{C}_{8} \mathrm{H}_{9} \mathrm{Cl}_{3}$
(d) $\mathrm{C}_{9} \mathrm{H}_{16} \mathrm{Br}_{2}$
(e) $\mathrm{C}_{10} \mathrm{H}_{12} \mathrm{~N}_{2} \mathrm{O}_{3}$
(f) $\mathrm{C}_{20} \mathrm{H}_{32} \mathrm{ClN}$

Shalini Tyagi

Numerade Educator

Problem 3

Diazepam, marketed as an antianxiety medication under the name Valium, has three rings, eight double bonds, and the formula $\mathrm{C}_{16} \mathrm{H}_{?} \mathrm{ClN}_{2} \mathrm{O}$. How many hydrogens does diazepam have? (Calculate the answer; don't count hydrogens in the structure.)

Lijeesh Krishnan

Lijeesh Krishnan

Numerade Educator

Problem 4

Give IUPAC names for the following compounds:
a.
b.
c.
d.
e.
f.
g.

Ronald Prasad

Numerade Educator

Problem 5

Draw structures corresponding to the following IUPAC names:
(a) 2-Methylhexa-1,5-diene
(b) 3 -Ethyl-2,2-dimethylhept-3-ene
(c) 2,3,3 -Trimethylocta-1,4,6-triene
(d) 3,4 -Diisopropyl- 2,5 -dimethylhex-3-ene

Lijeesh Krishnan

Lijeesh Krishnan

Numerade Educator

Problem 6

Name the following alkynes:
a.
b.
c.
d.
e.

George Bennett

Numerade Educator

Problem 7

Change the following old names to new, post-1993 names, and draw the structure of each compound:
(a) 2,5,5 -Trimethyl-2-hexene
(b) 2,2 -Dimethyl-3-hexyne

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 8

The sex attractant of the common housefly is an alkene named $c i s$ -tricos-9ene. Draw its structure. (Tricosane is the straight-chain alkane $\mathrm{C}_{23} \mathrm{H}_{48}$.)

Lijeesh Krishnan

Lijeesh Krishnan

Numerade Educator

Problem 9

Which of the following compounds can exist as pairs of cis-trans isomers? Draw each cis-trans pair, and indicate the geometry of each isomer.
(a) $\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}_{2}$
(b) $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}=\mathrm{CHCH}_{3}$
(c) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}=\mathrm{CHCH}_{3}$
(d) $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}=\mathrm{C}\left(\mathrm{CH}_{3}\right) \mathrm{CH}_{2} \mathrm{CH}_{3}$
(e) $\mathrm{ClCH}=\mathrm{CHCl}$
(f) $\operatorname{BrCH}=\mathrm{CHCl}$

Shalini Tyagi

Numerade Educator

Problem 10

Name the following alkenes, including the cis or trans designation:
a.
b.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 11

Name the following alkenes, including the cis or trans designation:
Which member in each of the following sets ranks higher?
(a) $-\mathrm{H}$ or $-\mathrm{CH}_{3}$
(b) $-\mathrm{Cl}$ or $-\mathrm{CH}_{2} \mathrm{Cl}$
(c) $-\mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Br}$ or $-\mathrm{CH}=\mathrm{CH}_{2}$
(d) $-\mathrm{NHCH}_{3}$ or $-\mathrm{OCH}_{3}$
(e) $-\mathrm{CH}_{2} \mathrm{OH}$ or $-\mathrm{CH}=\mathrm{O}$
(f) $-\mathrm{CH}_{2} \mathrm{OCH}_{3}$ or $-\mathrm{CH}=\mathrm{O}$

Vasu Makani

Numerade Educator

Problem 12

Rank the substituents in each of the following sets according to the sequence rules:
(a) $-\mathrm{CH}_{3},-\mathrm{OH},-\mathrm{H},-\mathrm{Cl}$
(b) $-\mathrm{CH}_{3},-\mathrm{CH}_{2} \mathrm{CH}_{3},-\mathrm{CH}=\mathrm{CH}_{2},-\mathrm{CH}_{2} \mathrm{OH}$
(c) $-\mathrm{CO}_{2} \mathrm{H},-\mathrm{CH}_{2} \mathrm{OH},-\mathrm{C} \equiv \mathrm{N},-\mathrm{CH}_{2} \mathrm{NH}_{2}$
(d) $-\mathrm{CH}_{2} \mathrm{CH}_{3},-\mathrm{C} \equiv \mathrm{CH},-\mathrm{C} \equiv \mathrm{N},-\mathrm{CH}_{2} \mathrm{OCH}_{3}$

Shalini Tyagi

Numerade Educator

Problem 13

Assign $E$ or $Z$ configuration to the double bonds in the following compounds:
a.
b.
c.
d.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 14

Assign $E$ or $Z$ configuration to the double bonds in the following compounds:

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 15

Name the following alkenes, and tell which compound in each pair is more stable:
a.
b.
c.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 16

Predict the products of the following reactions:
a.
b.
c.
d.

Anish Wadhwa

Numerade Educator

Problem 17

What alkenes would you start with to prepare the following products?
a.
b.
c.
d.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 18

Show the structures of the carbocation intermediates you would expect in the following reactions:
a.
b.

Ronald Prasad

Numerade Educator

Problem 19

Draw a skeletal structure of the following carbocation. Identify it as primary, secondary, or tertiary, and identify the hydrogen atoms that have the proper orientation for hyperconjugation in the conformation shown.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 20

What about the second step in the electrophilic addition of HCl to an alkenethe reaction of chloride ion with the carbocation intermediate? Is this step exergonic or endergonic? Does the transition state for this second step resemble the reactant (carbocation) or product (alkyl chloride)? Make a rough drawing of what the transition-state structure might look like.

Lainey Roebuck

Numerade Educator

Problem 21

On treatment with HBr, vinylcyclohexane undergoes addition and rearrangement to yield 1-bromo-1-ethylcyclohexane. Using curved arrows, propose a mechanism to account for this result.

Shalini Tyagi

Numerade Educator

Problem 22

Name the following alkenes, and convert each drawing into a skeletal structure:
a.
b.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 23

Assign $E$ or $Z$ stereochemistry to the double bonds in each of the following alkenes, and convert each drawing into a skeletal structure $($ red $=\mathrm{O},$ green $=\mathrm{Cl})$
a.
b.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 24

The following carbocation is an intermediate in the electrophilic addition reaction of HCl with two different alkenes. Identify both, and tell which $\mathrm{C}-\mathrm{H}$ bonds in the carbocation are aligned for hyperconjugation with the vacant $p$ orbital on the positively charged carbon.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 25

The following alkyl bromide can be made by HBr addition to three different alkenes. Show their structures.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 26

Calculate the degree of unsaturation in the following formulas, and draw five possible structures for each:
(a) $\mathrm{C}_{10} \mathrm{H}_{16}$
(b) $\mathrm{C}_{8} \mathrm{H}_{8} \mathrm{O}$
(c) $\mathrm{C}_{7} \mathrm{H}_{10} \mathrm{Cl}_{2}$
(d) $\mathrm{C}_{10} \mathrm{H}_{16} \mathrm{O}_{2}$
(e) $\mathrm{C}_{5} \mathrm{H}_{9} \mathrm{NO}_{2}$
(f) $\mathrm{C}_{8} \mathrm{H}_{10} \mathrm{ClNO}$

Anand Jangid

Numerade Educator

Problem 27

How many hydrogens does each of the following compounds have?
(a) $\mathrm{C}_{8} \mathrm{H}_{?} \mathrm{O}_{2}$, has two rings and one double bond
(b) $\mathrm{C}_{7} \mathrm{H}_{?} \mathrm{~N},$ has two double bonds
(c) $\mathrm{C}_{9} \mathrm{H}_{?} \mathrm{NO}$, has one ring and three double bonds

Anand Jangid

Numerade Educator

Problem 28

Loratadine, marketed as an antiallergy medication under the name Claritin, has four rings, eight double bonds, and the formula $\mathrm{C}_{22} \mathrm{H}_{?} \mathrm{ClN}_{2} \mathrm{O}_{2} .$ How many hydrogens does loratadine have? (Calculate your answer; don't count hydrogens in the structure.)

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 29

Name the following alkenes:
a.
b.
c.
d.
e.
f.

Nicholas Sacco

Numerade Educator

Problem 30

Draw structures corresponding to the following systematic names:
(a) $(4 E)-2,4$ -Dimethylhexa-1,4-diene
(b) cis-3,3-Dimethyl-4-propylocta-1,5-diene
(c) 4 -Methylpenta-1,2-diene
(d) $(3 E, 5 Z)-2,6$ -Dimethylocta- 1,3,5,7 -tetraene
(e) 3-Butylhept-2-ene
(f) trans-2,2,5,5-Tetramethylhex-3-ene

Anand Jangid

Numerade Educator

Problem 31

Name the following cycloalkenes:
a.
b.
c.
d.
e.
f.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 32

Ocimene is a triene found in the essential oils of many plants. What is its IUPAC name, including stereochemistry? Ocimene

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 33

$\alpha$ -Farnesene is a constituent of the natural wax found on apples. What is its IUPAC name, including stereochemistry? $\alpha$ -Farnesene

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 34

Menthene, a hydrocarbon found in mint plants, has the systematic name 1 -isopropyl-4-methylcyclohexene. Draw its structure

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 35

Draw and name the six alkene isomers, $\mathrm{C}_{5} \mathrm{H}_{10}$, including $E, Z$ isomers.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 36

There are seven isomeric alkynes with the formula $\mathrm{C}_{6} \mathrm{H}_{10} .$ Draw and name them.

Brittany Carnathan

Brittany Carnathan

Numerade Educator

Problem 37

Draw and name the 17 alkene isomers, $\mathrm{C}_{6} \mathrm{H}_{12}$, including $E, Z$ isomers.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 38

Tridec-1-ene-3,5,7,9,11-pentayne is a hydrocarbon isolated from sunflowers. Draw its structure. (Tridecane is the straight-chain alkane $\left.\mathrm{C}_{13} \mathrm{H}_{28} .\right)$

Lijeesh Krishnan

Lijeesh Krishnan

Numerade Educator

Problem 39

Rank the substituents in each of the following sets according to the Cahn-Ingold-Prelog sequence rules:
(a) $-\mathrm{CH}_{3},-\mathrm{Br},-\mathrm{H},-\mathrm{I}$
(b) $-\mathrm{OH},-\mathrm{OCH}_{3},-\mathrm{H},-\mathrm{CO}_{2} \mathrm{H}$
(c) $-\mathrm{CO}_{2} \mathrm{H},-\mathrm{CO}_{2} \mathrm{CH}_{3},-\mathrm{CH}_{2} \mathrm{OH},-\mathrm{CH}_{3}$
(d)
(e) $-\mathrm{CH}=\mathrm{CH}_{2},-\mathrm{CN},-\mathrm{CH}_{2} \mathrm{NH}_{2},-\mathrm{CH}_{2} \mathrm{Br}$
(f) $-\mathrm{CH}=\mathrm{CH}_{2},-\mathrm{CH}_{2} \mathrm{CH}_{3},-\mathrm{CH}_{2} \mathrm{OCH}_{3},-\mathrm{CH}_{2} \mathrm{OH}$

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 40

Assign $E$ or $Z$ configuration to the double bonds in each of the following compounds:

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 41

Which of the following $E, Z$ designations are correct, and which are incorrect?
a.
b.
c.
d.
e.
f.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 42

trans-But-2-ene is more stable than cis-but-2-ene by only $4 \mathrm{~kJ} / \mathrm{mol}$, but trans-2,2,5,5-tetramethylhex-3-ene is more stable than its cis isomer by $39 \mathrm{~kJ} / \mathrm{mol}$. Explain.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 43

Cyclodecene can exist in both cis and trans forms, but cyclohexene cannot. Explain. (Making molecular models is helpful.)

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 44

Normally, a trans alkene is more stable than its cis isomer. transCyclooctene, however, is less stable than cis-cyclooctene by $38.5 \mathrm{~kJ} / \mathrm{mol}$. Explain.

Shalini Tyagi

Numerade Educator

Problem 45

trans-Cyclooctene is less stable than cis-cyclooctene by $38.5 \mathrm{~kJ} / \mathrm{mol}$, but trans-cyclononene is less stable than cis-cyclononene by only $12.2 \mathrm{~kJ} / \mathrm{mol}$. Explain.

Shalini Tyagi

Numerade Educator

Problem 46

Tamoxifen, a drug used in the treatment of breast cancer, and clomiphene, a drug used as a fertility treatment, have similar structures but very different effects. Assign $E$ or $Z$ configuration to the double bonds in both compounds.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 47

Predict the major product in each of the following reactions:
a.
b.
c.
d.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 48

Predict the major product from addition of HBr to each of the following alkenes:
a.
b.
c.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 49

Predict the major alcohol product from acid-catalyzed addition of water to each of the following alkenes.
a.
b.
c.

Timothy Gailey

Numerade Educator

Problem 50

Each of the following carbocations can rearrange to a more stable ion. Propose structures for the likely rearrangement products.
(a) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2}^{+}$
(b)
(c)

Ronald Prasad

Numerade Educator

Problem 51

Addition of HCl to 1-isopropylcyclohexene yields a rearranged product. Propose a mechanism, showing the structures of the intermediates and using curved arrows to indicate electron flow in each step.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 52

Allene (propa-1,2-diene), $\mathrm{H}_{2} \mathrm{C}=\mathrm{C}=\mathrm{CH}_{2}$, has two adjacent double bonds. What kind of hybridization must the central carbon have? Sketch the bonding $\pi$ orbitals in allene. What shape do you predict for allene?

Ronald Prasad

Numerade Educator

Problem 53

The heat of hydrogenation for allene (Problem 7.52 ) to yield propane is $-295 \mathrm{~kJ} / \mathrm{mol}$, and the heat of hydrogenation for a typical monosubstituted alkene such as propene is $-126 \mathrm{~kJ} / \mathrm{mol}$. Is allene more stable or less stable than you might expect for a diene? Explain.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 54

Retin A, or retinoic acid, is a medication commonly used to reduce wrinkles and treat severe acne. How many different isomers arising from double-bond isomerizations are possible?

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 55

Fucoserratene and ectocarpene are sex pheromones produced by marine brown algae. What are their systematic names? (Ectocarpene is a bit difficult; make your best guess, and then check your answer in the Study Guide and Solutions Manual.)

Anand Jangid

Numerade Educator

Problem 56

Assign $E$ or $Z$ configuration to the double bond in the following compound. (It's a bit difficult, so check your answer in the Study Guide and Solutions Manual.)

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 57

tert-Butyl esters $\left[\mathrm{RCO}_{2} \mathrm{C}\left(\mathrm{CH}_{3}\right)_{3}\right]$ are converted into carboxylic acids $\left(\mathrm{RCO}_{2} \mathrm{H}\right)$ by reaction with trifluoroacetic acid, a reaction useful in protein synthesis (Section $19-7)$. Assign $E, Z$ designation to the double bonds of both reactant and product in the following scheme, and explain why there is an apparent change of double-bond stereochemistry

Ronald Prasad

Numerade Educator

Problem 58

Addition of HCl to 1 -isopropenyl-1-methylcyclopentane yields 1 -chloro1,2,2 -trimethylcyclohexane. Propose a mechanism, showing the structures of the intermediates and using curved arrows to indicate electron flow in each step.

Shalini Tyagi

Numerade Educator

Problem 59

Vinylcyclopropane reacts with HBr to yield a rearranged alkyl bromide. Follow the flow of electrons as represented by the curved arrows, show the structure of the carbocation intermediate in brackets, and show the structure of the final product.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 60

Calculate the degree of unsaturation in each of the following compounds:
(a) Cholesterol, $\mathrm{C}_{27} \mathrm{H}_{46} \mathrm{O}$
(b) $\mathrm{DDT}, \mathrm{C}_{14} \mathrm{H}_{9} \mathrm{Cl}_{5}$
(c) Prostaglandin $\mathrm{E}_{1}, \mathrm{C}_{20} \mathrm{H}_{34} \mathrm{O}_{5}$
(d) Caffeine, $\mathrm{C}_{8} \mathrm{H}_{10} \mathrm{~N}_{4} \mathrm{O}_{2}$
(e) Cortisone, $\mathrm{C}_{21} \mathrm{H}_{28} \mathrm{O}_{5}$
(f) Atropine, $\mathrm{C}_{17} \mathrm{H}_{23} \mathrm{NO}_{3}$

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 61

The isobutyl cation spontaneously rearranges to the tert-butyl cation by a hydride shift. Is the rearrangement exergonic or endergonic? Draw what you think the transition state for the hydride shift might look like according to the Hammond postulate. Isobutyl cation, tert-Butyl cation

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 62

Draw an energy diagram for the addition of HBr to pent-1-ene. Let one curve on your diagram show the formation of 1 -bromopentane product and another curve on the same diagram show the formation of 2 -bromopentane product. Label the positions for all reactants, intermediates, and products. Which curve has the higher-energy carbocation intermediate? Which curve has the higher-energy first transition state?

Lainey Roebuck

Numerade Educator

Problem 63

Make sketches of the transition-state structures involved in the reaction of HBr with pent-1-ene (Problem 7.62 ). Tell whether each structure resembles reactant or product.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 64

Limonene, a fragrant hydrocarbon found in lemons and oranges, is biosynthesized from geranyl diphosphate by the following pathway. Add curved arrows to show the mechanism of each step. Which step involves an alkene electrophilic addition? (The ion $\mathrm{OP}_{2} \mathrm{O}_{6}{ }^{4-}$ is the diphosphate ion, and "Base" is an unspecified base in the enzyme that catalyzes the reaction.)

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 65

epi-Aristolochene, a hydrocarbon found in both pepper and tobacco, is biosynthesized by the following pathway. Add curved arrows to show the mechanism of each step. Which steps involve alkene electrophilic addition(s), and which involve carbocation rearrangement(s)? (The abbreviation H-A stands for an unspecified acid, and "Base" is an unspecified base in the enzyme.)

Dr. Satish Ingale

Dr. Satish Ingale

Numerade Educator

Problem 66

Aromatic compounds such as benzene react with alkyl chlorides in the presence of $\mathrm{AlCl}_{3}$ catalyst to yield alkylbenzenes. The reaction occurs through a carbocation intermediate, formed by reaction of the alkyl chloride with $\mathrm{AlCl}_{3}\left(\mathrm{R}-\mathrm{Cl}+\mathrm{AlCl}_{3} \rightarrow \mathrm{R}^{+}+\mathrm{AlCl}_{4}-\right.$ ). How can you explain
the observation that reaction of benzene with 1 -chloropropane yields isopropylbenzene as the major product?

Lainey Roebuck

Numerade Educator

Problem 67

Reaction of 2,3 -dimethylbut-1-ene with HBr leads to an alkyl bromide, $\mathrm{C}_{6} \mathrm{H}_{13} \mathrm{Br}$. On treatment of this alkyl bromide with KOH in methanol, elimination of HBr occurs and a hydrocarbon that is isomeric with the starting alkene is formed. What is the structure of this hydrocarbon, and how do you think it is formed from the alkyl bromide?

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator