Organic Chemistry

John McMurry

Chapter 7

Alkenes: Structure and Reactivity - 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 $\mathrm{C}_{16} \mathrm{H}_2 \mathrm{ClN}_2 \mathrm{O}$. How many hydrogens does diazepam have? (Calculate the answer; don't count hydrogens in the structure.)
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Lijeesh Krishnan

Lijeesh Krishnan

Numerade Educator

Problem 4

Give IUPAC names for the following compounds:

Ricajoy Montero

Ricajoy Montero

Numerade Educator

Problem 5

Draw structures corresponding to the following IUPAC names:
(a) 2-Methyl-1,5-hexadiene
(b) 3-Ethyl-2,2-dimethyl-3-heptene
(c) 2,3,3-Trimethyl-1,4,6-octatriene
(d) 3,4-Diisopropyl-2,5-dimethyl-3-hexene

Lijeesh Krishnan

Lijeesh Krishnan

Numerade Educator

Problem 6

Name the following cycloalkenes:
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Bobby Barnes

University of North Texas

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) 2,3-Dimethyl-1,3-cyclohexadiene

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 8

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

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 9

Which of the following compounds can exist as pairs of cis-trans isomers? Draw each 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) $\mathrm{BrCH}=\mathrm{CHCl}$

Shalini Tyagi

Numerade Educator

Problem 10

Name the following alkenes, including a cis or trans designation:
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Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 11

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 $-\mathrm{CH}=\mathrm{O}$

Grigoriy Sereda

Grigoriy Sereda

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 following alkenes:
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Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 14

Assign stereochemistry (E or Z) to the double bond in the following compound, and convert the
drawing into a skeletal structure (red = O):
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Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 15

Name the following alkenes, and tell which compound in each pair is more stable:
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Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 16

Predict the products of the following reactions:
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Zubair Abdulla

Numerade Educator

Problem 17

What alkenes would you start with to prepare the following products?
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Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 18

Show the structures of the carbocation intermediates you would expect in the following reactions:
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Anish Wadhwa

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.
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Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 20

What about the second step in the electrophilic addition of HCl to an alkene—the 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.
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Shalini Tyagi

Numerade Educator

Problem 22

Name the following alkenes, and convert each drawing into a skeletal structure:
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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 = O, green = Cl):
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Nicole Smina

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 C?H bonds in the carbocation are aligned for
hyperconjugation with the vacant p orbital on the positively charged carbon.
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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.
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Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 26

Predict the major product and show the complete mechanism for each of the following electrophilic
addition reactions.
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Lainey Roebuck

Numerade Educator

Problem 27

Each of the following electrophilic addition reactions involves a carbocation rearrangement.
Predict the product and draw the complete mechanism of each using curved arrows.
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Nicole Krahulik

Nicole Krahulik

Numerade Educator

Problem 28

When 1,3-butadiene reacts with 1 mol of HBr, two isolable products result. Propose mechanisms
for both.
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Shalini Tyagi

Numerade Educator

Problem 29

When methyl vinyl ether reacts with a strong acid, H+
adds to C2 instead of C1 or the oxygen atom.
Explain.
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Anand Jangid

Numerade Educator

Problem 30

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.
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Ronald Prasad

Numerade Educator

Problem 31

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

Numerade Educator

Problem 32

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 OP2O6
4? is the diphosphate ion, and
“Base” is an unspecified base in the enzyme that catalyzes the reaction.)
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Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 33

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.)
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Dr. Satish Ingale

Dr. Satish Ingale

Numerade Educator

Problem 34

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 35

How many hydrogens does each of the following compounds have?
(a) $\mathrm{C}_8 \mathrm{H}_2 \mathrm{O}_2$, has two rings and one double bond (b) $\mathrm{C}_7 \mathrm{H}_2 \mathrm{~N}$, has two double bonds
(c) $\mathrm{C}_9 \mathrm{H}_2 \mathrm{NO}$, has one ring and three double bonds

Anand Jangid

Numerade Educator

Problem 36

Loratadine, marketed as an antiallergy medication under the brand name Claritin, has four rings, eight double bonds, and the formula $\mathrm{C}_{22} \mathrm{H}_3 \mathrm{ClN}_2 \mathrm{O}_2$. How many hydrogens does loratadine have? (Calculate your answer; don't count hydrogens in the structure.)
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Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 37

Name the following alkenes:
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Lottie Adams

Numerade Educator

Problem 38

Draw structures corresponding to the following systematic names:
(a) (4E)-2,4-Dimethyl-1,4-hexadiene (b) cis-3,3-Dimethyl-4-propyl-1,5-octadiene
(c) 4-Methyl-1,2-pentadiene (d) (3E,5Z)-2,6-Dimethyl-1,3,5,7-octatetraene
(e) 3-Butyl-2-heptene (f) trans-2,2,5,5-Tetramethyl-3-hexene

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 40

Name the following cycloalkenes:
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Bobby Barnes

University of North Texas

Problem 41

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

Grigoriy Sereda

Numerade Educator

Problem 42

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 43

Draw and name the six alkene isomers, $\mathrm{C}_5 \mathrm{H}_{10}$, including $E, Z$ isomers.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 44

Draw and name the 17 alkene isomers, $\mathrm{C}_6 \mathrm{H}_{12}$, including $E, Z$ isomers.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 45

Rank the following sets of substituents according to the Cahn–Ingold–Prelog sequence rules:
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Lainey Roebuck

Numerade Educator

Problem 46

Assign E or Z configuration to each of the following compounds:
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Ronald Prasad

Numerade Educator

Problem 47

Which of the following E,Z designations are correct, and which are incorrect?
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Ashley High

Numerade Educator

Problem 48

Rank the double bonds according to their increasing stability.
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Lainey Roebuck

Numerade Educator

Problem 49

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

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 50

Cyclodecene can exist in both cis and trans forms, but cyclohexene cannot. Explain.

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 51

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

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 52

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 53

Tamoxifen, a drug used in the treatment of breast cancer, and clomiphene, a drug used in 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 54

Rank the following carbocations according to their increasing stability.
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KS

Karli Sipps

Numerade Educator

Problem 55

Use the Hammond Postulate to determine which alkene in each pair would be expected to form a
carbocation faster in an electrophilic addition reaction.
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Lainey Roebuck

Numerade Educator

Problem 56

The following carbocations can be stabilized by resonance. Draw all the resonance forms that would
stabilize each carbocation.
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Anand Jangid

Numerade Educator

Problem 57

Predict the major product in each of the following reactions:
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Check back soon!

Problem 58

Predict the major product from addition of HBr to each of the following alkenes:
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Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 59

Alkenes can be converted into alcohols by acid-catalyzed addition of water. Assuming that Markovnikov's rule is valid, predict the major alcohol product from each of the following alkenes.
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Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 60

Each of the following carbocations can rearrange to a more stable ion. Propose structures for the
likely rearrangement products.
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Nicole Krahulik

Nicole Krahulik

Numerade Educator

Problem 61

Allene (1,2-propadiene), $\mathrm{H}_2 \mathrm{C}=\mathrm{C}=\mathrm{CH}_2$, 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 62

The heat of hydrogenation for allene (Problem 7-61) to yield propane is $-295 \mathrm{~kJ} / \mathrm{mol}$, and the heat of hydrogenation for a typical monosubstituted alkene, such as propene, is $-125 \mathrm{~kJ} / \mathrm{mol}$. Is allene more stable or less stable than you might expect for a diene? Explain.

Lainey Roebuck

Numerade Educator

Problem 63

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

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 64

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

Numerade Educator

Problem 65

tert-Butyl esters [RCO2C(CH3)3] are converted into carboxylic acids (RCO2H) by reaction with
trifluoroacetic acid, a reaction useful in protein synthesis (Section 26.7). 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 in double-bond stereochemistry:
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Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 66

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.
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Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 67

Calculate the degree of unsaturation in each of the following formulas:
(a) Cholesterol, $\mathrm{C}_{27} \mathrm{H}_{46} \mathrm{O}$
(b) 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 68

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.
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Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 69

Draw an energy diagram for the addition of $\mathrm{HBr}$ to 1-pentene. 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 70

Sketch the transition-state structures involved in the reaction of $\mathrm{HBr}$ with 1-pentene (Problem 7-69). Tell whether each structure resembles reactant or product.

Lainey Roebuck

Numerade Educator

Problem 71

Aromatic compounds such as benzene react with alkyl chlorides in the presence of $\mathrm{AlCl}_3$ catalyst to yield alkylbenzenes. This reaction occurs through a carbocation intermediate, formed by reaction of the alkyl chloride with $\mathrm{AlCl}_3\left(\mathrm{R}-\mathrm{Cl}+\mathrm{AlCl}_3 \longrightarrow \mathrm{R}^{+}+\mathrm{AlCl}_4{ }^{-}\right)$. How can you explain the observation that reaction of benzene with 1-chloropropane yields isopropylbenzene as the major product?

Lainey Roebuck

Numerade Educator

Problem 72

Reaction of 2,3-dimethyl-1-butene with HBr leads to an alkyl bromide, C6H13Br. 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