Organic Chemistry

T.W. Graham Solomons, Craig B. Fryhle, Scott A. Snyder

Chapter 8

Alkenes and Alkynes II - all with Video Answers

Educators

Chapter Questions

Problem 1

Give the structure and name of the product that would be obtained from the ionic addition of IBr to propene.

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Kaitlynn Wade

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Problem 2

Write mechanisms for the following addition reactions:
(EQUATION CAN'T COPY)

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Problem 3

Provide mechanistic explanations for the following observations:
(EQUATION CAN'T COPY)

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Problem 4

(a) Write a mechanism for the following reaction.
(EQUATION CAN'T COPY)
(b) What general conditions would you use to ensure a good yield of the product?
(c) What general conditions would you use to carry out the reverse reaction, i.e., the dehydration of cyclohexanol to produce cyclohexene?
(d) What product would you expect to obtain from the acid-catalyzed hydration of 1-methylcyclohexene? Explain your answer.

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Problem 5

In one industrial synthesis of ethanol, ethene first undergoes an addition reaction with sulfuric acid, and this product undergoes hydrolysis to ethanol. Write a mechanism for the addition of sulfuric acid to ethene.

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Problem 6

Write a mechanism that shows how 2,3 -dimethyl-2-butanol is formed in the acidcatalyzed hydration of 3,3 -dimethyl-1-butene.

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Problem 7

The following order of reactivity is observed when the following alkenes are subjected to acid-catalyzed hydration:
$$
\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}=\mathrm{CH}_{2}>\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}_{2}>\mathrm{CH}_{2}=\mathrm{CH}_{2}
$$
Explain this order of reactivity.

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Problem 8

Write a mechanism for the following reaction.
(EQUATION CAN'T COPY)

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Problem 9

Write the structure of the appropriate alkene and specify the reagents needed to synthesize each of the following alcohols by oxymercuration-demercuration:
(EQUATION CAN'T COPY)

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Problem 10

(a) Write a mechanism for the solvomercuration step of the ether synthesis just shown.
(b) Show how you would use solvomercuration-demercuration to prepare tert-buryl methyl ether. (c) Propose a reason why $\mathrm{Hg}\left(\mathrm{O}_{2} \mathrm{CCF}_{3}\right)_{2}$ is more reactive than $\mathrm{Hg}(\mathrm{OAc})_{2}$

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Problem 11

Specify the alkene needed for synthesis of each of the following alkylboranes by hydroboration:
(EQUATION CAN'T COPY)

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Problem 12

Treating a hindered alkene such as 2 -methyl-2-butene with BH $_{3}:$ THF leads to the formation of a dialkylborane instead of a trialkylborane. When 2 mol of 2 -methyl-2-butene is added to 1 mol of $\mathrm{BH}_{3}$, the product formed is bis( 3 -methyl-2-butyl) borane, nicknamed "disiamylborane." Write its structure. Bis( 3 -methyl-2-butyl) borane is a useful reagent in certain syntheses that require a sterically hindered borane. (The name "disiamyl" comes from "disecondary-iso-amyl," a completely unsystematic and unacceptable name. The name "amyl" is an old common name for a five-carbon alkyl group.)

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Problem 13

Specify the appropriate alkene and reagents for synthesis of each of the following alcohols by hydroboration-oxidation.
(EQUATION CAN'T COPY)

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Problem 14

Starting with any needed alkene (or cycloalkene) and assuming you have deuterioacetic acid $\left(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{D}\right)$ available, outline syntheses of the following deuterium-labeled compounds.
a. (EQUATION CAN'T COPY) b. (EQUATION CAN'T COPY) c. (EQUATION CAN'T COPY) (d) Assuming you also have available $\mathrm{BD}_{3}:$ THF and $\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{T}$, can you suggest a synthesis of the following?(EQUATION CAN'T COPY)

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Problem 15

Write a mechanism to explain the following reaction.
(EQUATION CAN'T COPY)

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Problem 16

When ethene gas is passed into an aqueous solution containing bromine and sodium chloride, the products of the reaction are the following:
(EQUATION CAN'T COPY)

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Problem 17

What products would you expect from each of the following reactions?
(EQUATION CAN'T COPY)

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Problem 18

Starting with cyclohexene and using any other needed reagents, outline a synthesis of
7,7 -dibromobicyclo[4.1.0]heptane.

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Problem 19

Treating cyclohexene with 1,1 -diodoethane and a zinc-copper couple leads to two isomeric products. What are their structures?

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Problem 20

Specify the alkene and reagents needed to synthesize each of the following diols.
(EQUATION CAN'T COPY)

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Problem 21

Predict the products of the following ozonolysis reactions.
(EQUATION CAN'T COPY)

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Problem 22

Write the structures of the alkenes that would yield the following carbonyl compounds when treated with ozone and then with dimethyl sulfide.
(EQUATION CAN'T COPY)

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Problem 23

Alkenes are more reactive than alkynes toward addition of electrophilic reagents (i.e., $\mathrm{Br}_{2}, \mathrm{Cl}_{2},$ or $\mathrm{HCl}$ ). Yet when alkynes are treated with one molar equivalent of these same electrophilic reagents, it is easy to stop the addition at the "alkene stage." This appears to be a paradox and yet it is not. Explain.

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Problem 24

A, $\mathbf{B},$ and $\mathbf{C}$ are alkynes. Elucidate their structures and that of $\mathbf{D}$ using the following reaction roadmap.
(EQUATION CAN'T COPY)

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Problem 25

How would you modify the procedure given in Solved Problem 8.8 so as to synthesize a racemic form of $(3 R, 4 R)$ - and $(3 S, 4 S)-3,4$ -dibromohexane?

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Problem 26

Write structural formulas for the products that form when 1 -butene reacts with each of the following reagents:
(a) HI
(h) HCl
(b) $\mathrm{H}_{2}, \mathrm{Pt}$
(i) $\mathrm{O}_{3},$ then $\mathrm{Me}_{2} \mathrm{S}$
(c) Dilute H $_{2}$ SO $_{4}$ warm
(i) $\mathrm{OsO}_{4},$ then $\mathrm{NaHSO}_{3} / \mathrm{H}_{2} \mathrm{O}$
(d) HzO, cat. H, SO,
(k) $\mathrm{KMnO}_{4}, \mathrm{HO}^{-},$ heat, then $\mathrm{H}_{3} \mathrm{O}^{+}$
(c) HBr
(i) Hg(OAc)_ in THF and $\mathrm{H}_{2} \mathrm{O},$ then $\mathrm{NaBH}_{4}, \mathrm{HO}^{-}$
(f) Br $_{2}$ (m) BHs:THF, then $\mathrm{H}_{2} \mathrm{O}_{2}, \mathrm{HO}^{-}$
(g) $\mathrm{Br}_{2}$ in $\mathrm{H}_{2} \mathrm{O}$

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Problem 27

Repeat Exercise 8.26 using 1 -methylcyclopentene instead of 1 -butene.

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Problem 28

Write structures for the major organic products from the following reactions. Show stereoisomers where applicable.
(EQUATION CAN'T COPY)

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Problem 29

Give the structure of the products that you would expect from the reaction of 1 -butyne with:
(a) One molar equivalent of $B r_{2}$
(c) $\mathrm{H}_{2}, \mathrm{N}_{2} \mathrm{B}(\mathrm{P}-2)$
(b) One molar equivalent of HBr
( $\mathfrak{f}$ NaNH $_{2}$ in liquid $\mathrm{NH}_{3}$, then $\mathrm{CH}_{3}$.
(c) Two molar equivalents of HBr
(g) $\mathrm{NaNH}_{2}$ in liquid $\mathrm{NH}_{3},$ then $\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CBr}$
(d) $\mathrm{H}_{2}$ (in excess)/Pt

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Problem 30

Give the structure of the products you would expect from the reaction (if any) of 2 -butyne with:
(a) One molar equivalent of HBr
(b) Two molar equivalents of HBr
(c) One molar equivalent of Br $_{2}$
(d) Two molar equivalents of $\mathrm{Br}_{2}$
(e) $\mathrm{H}_{2}, \mathrm{Ni}_{2} \mathrm{B}(\mathrm{P}-2)$
(f) One molar equivalent of HCl
(g) Li/liquid $\mathrm{NH}_{3}$
(h) $\mathrm{H}_{2}$ (in excess), $\mathrm{Pt}$
(i) Two molar equivalents of $\mathrm{H}_{2}, \mathrm{Pt}$
(j) Hor $\mathrm{KMnO}_{4}, \mathrm{HO}^{-},$ then $\mathrm{H}_{3} \mathrm{O}^{+}$
(k) $\mathrm{O}_{3},$ then HOAC
(1) $\mathrm{NaNH}_{2}$, liquid $\mathrm{NH}_{3}$

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Problem 31

Write structures for the major organic products from the following reactions. Show stercoisomers where applicable.
(EQUATION CAN'T COPY)

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Problem 32

Show how 1 -butyne could be synthesized from each of the following:
$\begin{array}{llll}\text { (a) } \text { 1-Butene } & \text { (b) 1-Chlorobutanc } & \text { (c) 1-Chloro-1-butene } & \text { (d) 1,1-Dichlorobutane } & \text { (e) Ethyne and ethyl bromide }\end{array}$

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Problem 33

Starting with 2 -methylpropene (isobutylene) and using any other needed reagents, show how each of the following could be synthesized.
(EQUATION CAN'T COPY)

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Problem 34

Write a three-dimensional formula for the product formed when 1-methylaydohexene is treated with each of the following reagents. In each case, designate the location of deuterium or tritium atoms.
(a) $(1) \mathrm{BH}_{3}: \mathrm{THF},(2) \mathrm{CH}_{3} \mathrm{CO}_{2} \top$
(c) (1) BD $_{3}:$ THF, (2) NaOH, $\mathrm{H}_{2} \mathrm{O}_{2}, \mathrm{H}_{2} \mathrm{O}$
(b) $(1) \mathrm{BD}_{3}: \mathrm{THF},(2) \mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{D}$

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Problem 35

Write a mechanism that accounts for the formation of ethyl isopropyl tether as one of the products in the following reaction.
(EQUATION CAN'T COPY)

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Problem 36

When, in separate reactions, 2 -methylpropene, propene, and ethene are allowed to react with HI under the same conditions (i.e... identical concentration and temperature), 2 -methypropene is found to react fastest and ethene slowest. Provide an explanation for these relative rates.

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Problem 37

Propose a mechanism that accounts for the following reaction.
(EQUATION CAN'T COPY)

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Problem 38

When 3,3 -dimethyl-2-butanol is treated with concentrated Hl, a rearrangement takes place. Which alky liodide would you expect from the reaction? (Show the mechanism by which it is formed.)

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Problem 39

Write stereochemical formulas for all of the products that you would expect from each of the following reactions. (You may find models helpful.)
(EQUATION CAN'T COPY)

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Problem 40

Give ( $R, S$ ) designations for each different compound given as an answer to Problem $8.39 .$

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Problem 41

The double bond of tetrachlorocthene is underectable in the bromine test for unsaturation. Give a plausible explanation for this behavior

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Problem 42

Propose a mechanism that explains formation of the products from the following reaction, including the distribution of the products as major and minor.
(EQUATION CAN'T COPY)

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Problem 43

Write a mechanism that explains the following reaction.
(EQUATION CAN'T COPY)

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Problem 44

Write a mechanism for the following reaction.
(EQUATION CAN'T COPY)

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Problem 45

Write a mechanism that explains formation of the products shown in the following reaction.
(EQUATION CAN'T COPY)

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Problem 46

Myrcene, a fragrant compound found in bayberry wax, has the formula $C_{10} H_{16}$ and is known contain any triple bonds.
(a) What is the index of hydrogen deficiency of myrcene? When treated with excess hydrogen and a platinum caralyst, myrcene is converted to a compound ( $\mathbf{A}$ ) with the formula $\mathrm{C}_{10} \mathrm{H}_{22}$
(b) How many rings does myrcene contain?
(c) How many double bonds? Compound A can be identified as 2,6 -dimethyloctane. Ozonolysis of myrcene followed by treatment with dimechyl sulfide yields 2 mol of formaldehyde (HCHO), 1 mol of acetone $\left(\mathrm{CH}_{3} \mathrm{COCH}_{3}\right),$ and a third compound (B) with the formula $\mathrm{c}_{3} \mathrm{H}_{3} \mathrm{O}_{3}$
(d) What is the structure of compound B?
(e) What is the structure of myrcene?

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Problem 47

Farnesene (below) is a compound found in the waxy coating of apples, while geranial is a molecule with a similar structure that is a component of lemongrass oil. (a) Give the structure and IUPAC name of the product formed when farnesene is allowed to react with excess hydrogen in the presence of a platinum catalyst. (b) How many stercoisomers of the product from part a are possible? (c) Write structural formulas for the products that would be formed when geranial is treated with ozone and then with dimethyl sulfide (Me,S).
(EQUATION CAN'T COPY)

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Problem 48

limonene is a compound found in orange oil and lemon oil. When limonene is treated with excess hydrogen and a platinum catalyst, the product of the reaction is 1-isopropyl-4-methylcyclohexane. When limonene is treated with ozone and then with dimethyl sulfide (Me,S), the products of the reaction are formaldehyde (HCHO) and the following compound. Write a structural formula for limonene.
(EQUATION CAN'T COPY)

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Problem 49

Pheromones (Section 4.7) are substances secreted by animals that produce a specific behavioral response in other members of the same species. Pheromones are effective at very low concentrations and include sex attractants, warning substances, and "aggregation" compounds. The sex attractant pheromone of the codling moth has the molecular formula $\mathrm{C}_{13} \mathrm{H}_{24} \mathrm{O}$. Using information you can glean from the following reaction diagram, deduce the structure of the codling moth sex pheromone. The double bonds are known (on the basis of other evidence) to be $(27,6 E)$
(EQUATION CAN'T COPY)

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Problem 50

Synthesize the following compound starting with ethyne and 1-bromopentane as your only organic reagents (except for solvents) and using any needed inorganic compounds.
(EQUATION CAN'T COPY)

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Problem 51

Predict features of their IR spectra that you could use to distinguish between the members of the following pairs of compounds. You may find the IR chart in the end-papers of the book and Table 2.1 useful.
(a) Pentane and 1 -pentyne
(b) Pentane and 1 -pentene
(c) 1 -Pentene and 1 -pentyne
(d) Pentane and 1 -bromopentane
(e) 2 -Pentyne and 1 -pentyne
(f) 1 -Pentenc and 1 -pentanol
(g) Pentane and 1 -pentanol
(h) 1 -Bromo- 2 -pentene and 1 -bromopentane
(i) 1 -Pentanol and 2 -penten- 1 -ol

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Problem 52

8.52 Deduce the structures of compounds $\mathbf{A}, \mathbf{B},$ and $\mathbf{C},$ which all have the formula $\mathrm{C}_{6} \mathrm{H}_{10} .$ As you read the information that follows, draw reaction flowcharts (roadmaps) like those in Problems 8.24 and $8.49 .$ This approach will help you solve the problem. All three compounds rapidly decolorize bromine; all three are soluble in cold concentrated sulfuric acid. Compound A has an absorption in its IR spectrum at about $3300 \mathrm{cm}^{-1}$, but compounds $\mathrm{B}$ and $\mathrm{C}$ do not. Compounds $\mathrm{A}$ and $\mathrm{B}$ both yield hexane when they are treated with excess hydrogen in the presence of a platinum catalyst. Under these conditions Cabsorbs only one molar equivalent of hydrogen and gives a product with the formula $\mathrm{C}_{6} \mathrm{H}_{12} .$ When $\mathrm{A}$ is oxidized with hot basic $\mathrm{KMnO}_{4}$ and the resulting solution acidified,the only organic product that can be isolated is(FIGURE CAN'T COPY) Similar oxidation of B gives only (FIGURE CAN'T COPY) and similar treatment of $\mathbf{C}$ gives only $\mathrm{HO}$ (FIGURE CAN'T COPY)

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Problem 53

Ricinoleic acid, a compound that can be isolated from castor oil, has the structure $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{5} \mathrm{CHOHCH}_{2} \mathrm{CH}=\mathrm{CH}\left(\mathrm{CH}_{2}\right)_{7} \mathrm{CO}_{2} \mathrm{H}$
(a) How many stereoisomers of this structure are possible? $\quad$ (b) Write these structures.

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Problem 54

There are two dicarboxylic acids with the general formula $\mathrm{HO}_{2} \mathrm{CCH}=\mathrm{CHCO}_{2} \mathrm{H}$ One dicarboxylic acid is called maleic acid; the other is called fumaric acid. When treated with $\mathrm{OsO}_{4}$ followed by $\mathrm{NaHSO}_{3} / \mathrm{H}_{2} \mathrm{O},$ malcic acid yields meso-tartaric acid and fumaric acid yiclds $(\pm)$ -tartaric acid. Show how this information allows one to write stereochemical formulas for malcic acid and fumaric acid.

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Problem 55

Use your answers to the preceding problem to predict the stereochemical outcome of the addition of bromine to maleic acid and to fumaric acid. (a) Which dicarboxylic acid would add bromine to yield a meso compound? (b) Which would yield a racemic form?

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Problem 56

Alkyl halides add to alkenes in the presence of AICla; yiclds are the highest when tertiary halides are used. Predict the outcome of the reaction of tert-pentyl chloride ( 1 -chloro-2, , - dimethylpropane) with propene and specify the mechanistic steps.

Lottie Adams

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Problem 57

Make a reaction flowchart (roadmap diagram), as in previous problems, to organize the information provided to solve this problem. An optically active compound $\mathbf{A}$ (assume that it is dextrorotatory) has the molecular formula $\mathrm{C}_{7} \mathrm{H}_{11} \mathrm{Br}$. A reacts with hydrogen bromide, in the absence of peroxides, to yield isomeric products, B and C, with the molecular formula $\mathrm{C}_{7} \mathrm{H}_{12} \mathrm{Br}_{2} .$ Compound $\mathrm{B}$ is optically active; $\mathrm{C}$ is not. Treating B with 1 mol of potassium tert-butoxide yields ( $+$ )-A. Treating $\mathbf{C}$ with 1 mol of potassium tert-butoxide yields $(\pm)$ -A. Treating A with potassium tert-butoxide yields $\mathbf{D}\left(\mathrm{C}_{7} \mathrm{H}_{10}\right)$ Subjecting 1 mol of $\mathbf{D}$ to ozonolysis followed by treatment with dimethyl sulfide $$\left(\mathrm{Me}_{2} \mathrm{S}\right)$$ yields 2 mol of formaldehyde and 1 mol of 1,3 -cyclopentanedione. Propose stereochemical formulas for $\mathbf{A}, \mathbf{B}, \mathbf{C}$ and $\mathbf{D}$ and outline the reactions involved in these transformations.

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Problem 58

An optically active compound D has the molecular formula $\mathrm{C}_{6} \mathrm{H}_{10}$ and shows a peak at about $3300 \mathrm{cm}^{-1}$ in its IR spectrum. On catalytic hydrogenation D yields $\mathbf{E}\left(\mathrm{C}_{6} \mathrm{H}_{14}\right)$ Compound $\mathbf{E}$ is optically inactive and cannot be resolved. Propose structures for $\mathbf{D}$ and $\mathbf{E}$.

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Problem 59

For each of the following questions, please provide a route that could reasonably be expected to convert the starting material into the final product. In each case, more than one reaction is required, and reactions you have learned in previous chapters may be needed to solve the problem.
(FIGURE CAN'T COPY)

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Problem 60

For each of the following, identify the product (represented by $\mathbf{A}, \mathbf{B},$ and $\mathbf{C}$ ) that would be formed through the indicated sequence of steps from the given starting material.
(EQUATION CAN'T COPY)(FIGURE CAN'T COPY)

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Problem 61

Working backwards, deduce the starting material that led to the indicated product through the defined reactions.
(FIGURE CAN'T COPY)(EQUATION CAN'T COPY)

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Problem 62

Propose a mechanism that explains the following transformation. (Note its similarity to the cyclization of squalene oxide to lanosterol, as shown in "The Chemistry of.... Cholesterol Biosynthesis." in WileyPLUS.)
(FIGURE CAN'T COPY)

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Problem 63

$$\text { Triethylamine, }\left(\mathrm{C}_{2} \mathrm{H}_{5}\right)_{3} \mathrm{N}$$ like all amines, has a nitrogen atom with an unshared pair of electrons. Dichlorocarbene also has an unshared pair of electrons. Both can be represented as shown below. Draw the structures of compounds $\mathbf{D}, \mathbf{E},$ and $\mathbf{F}$ $$\begin{aligned}
&\left(\mathrm{C}_{2} \mathrm{H}_{5}\right)_{3} \mathrm{N}:+: \mathrm{CCl}_{2} \longrightarrow \mathrm{D}\\
&\mathbf{D} \longrightarrow \mathbf{E}+\mathrm{C}_{2} \mathrm{H}_{4}\\
&\mathbf{E} \stackrel{\mathrm{H}_{2} \mathrm{O}}{\longrightarrow} \mathbf{F}
\end{aligned}$$ (an unstable adduct)
(by an intramolecular E2 reaction)
(Water effects a replacement that is the reverse of that used to make gem-dichlorides.)

Narayan Hari

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