Additional Problems 9

Visualizing Chemistry

Problem 9.23
Give IUPAC names for the following compounds:

(a)

A ball-and-stick model of six-carbon chain with hydroxyl on C 3 and methyl on C 5 position.

(b)

A ball-and-stick model of cyclohexane with hydroxyl group on C 1 and methyl on C 3 position.

(c)

A ball-and-stick model of cyclopentane linked to a carbon atom that has H, methyl, and O H substituents.

(d)

A ball-and-stick model of a benzene with O H on C 1, a nitro group on C 3 and a methyl group on C 4 position.

Problem 9.24
Draw the structure of the carbonyl compound(s) from which each of the following alcohols might have been prepared, and show the products you would obtain by treatment of each alcohol with (1) Na metal, (2) SOCl2, and (3) Dess–Martin periodinane.

(a)

A ball-and-stick model of a six-carbon chain with hydroxyl on C 2, and methyl group on C 5 position.

(b)

A ball-and-stick model of five carbon chain with hydroxyl on C 1, and methyl group on C 3 position.

Problem 9.25
Predict the product from reaction of the following substance (reddish brown = Br) with:

A ball-and-stick model of benzene with bromine on C 1, C 3 of benzene has the substituent 2-butanol attached by C 3 of 2-butanol.

(a) PBr3

(b) Aqueous H2SO4

(c) SOCl2

(d) Dess–Martin periodinane

Problem 9.26
Predict the product from reaction of the following substance with:

A ball-and-stick model of a five-carbon chain with C O O C H 3 on C 1, and a methyl group on C 4 position.

(a) NaBH4; then H3O+

(b) 2 CH3CH2MgBr; then H3O+

Problem 9.27
Name and assign R or S stereochemistry to the product(s) you would obtain by reaction of the following substance with ethylmagnesium bromide. Is the product chiral? Is it optically active? Explain.

A ball-and-stick model of a five-carbon chain with keto group on C 2, and C 3 has a methyl group.

Problem 9.28
Give IUPAC names for the following compounds (red = O; reddish brown = Br; yellow = S):

(a)

The ball-and-stick model of the compound in which a six-membered ring is bonded with an ethyl group via an ether linkage.

(b)

The ball-and-stick model of the compound in which a five-membered cyclic ring is bonded with an ethyl group to which a thiol group is bonded.

Problem 9.29
Show the product, including stereochemistry, of the following reaction:

The ball-and-stick model of the reactant having a six-membered ring fused with an epoxide ring reacts with methyl magnesium bromide, ether, and hydronium ion. The product is unknown.

Mechanism Problems

Problem 9.30
Evidence for the intermediate carbocations in the acid-catalyzed dehydration of alcohols comes from the observation that rearrangements sometimes occur. Propose a mechanism to account for the formation of 2,3-dimethyl-2-butene from 3,3-dimethyl-2-butanol.

3,3-dimethyl-2-butanol reacts with sulfuric acid to form 2,3-dimethyl-2-butene and water.

Problem 9.31
Epoxides react with Grignard reagents to yield alcohols. Propose a mechanism.

cyclopentane with dashed hydrogen and wedged hydroxyl on C 1 and wedged hydrogen and dashed methyl on C 2.

Problem 9.32
Reduction of 2-butanone with NaBH4 yields 2-butanol. Is the product chiral? Is it optically active? Explain.

 

Problem 9.33
The conversion of 3° alcohols into 3° alkyl halides under acidic conditions involves two cationic intermediates. For each reaction, draw the complete mechanism using curved arrows.

(a)

1-methylcyclohexanol reacts with H Cl to form 1-chloro-1-methylcyclohexane.

(b)

2-methylbutan-2-ol reacts with H Br to form 2-bromo-2-methylbutane.

(c)

Two fused cyclohexane rings with a hydroxyl at a bridgehead carbon reacts with H Cl to substitute chlorine for the hydroxyl group.

Problem 9.34
Identify the type of substitution mechanism (SN1, SN2) involved in the conversion of the following alcohols into the corresponding alkyl halide.

(a)

2-methylbutan-2-ol reacts with H Cl to form 2-chloro-2-methylbutane.

(b)

2-butanol reacts with P Br 3 to form 2-bromobutane.

Problem 9.35
The conversion of 3° alcohols into alkenes under acidic conditions involves two cationic intermediates. For each reaction, draw the complete mechanism using curved arrows.

(a)

Reaction equation showing the acid-catalyzed dehydration of 1-methylcyclopentanol with $H_3O^+$ to form 1-methylcyclopentene.

(b)

2-methylbutan-2-ol reacts with hydronium to form 2-methylbut-2-ene.

(c)

Methanol with two methyl and one phenyl substituents reacts with hydronium to form 1-methyl-1-phenylethene

Problem 9.36
Phenols generally have lower pKa’s than alcohols because of resonance stabilization with the aromatic ring. Draw all of the resonance contributors for the following phenolate ions.

(a)

Chemical structure of 4-methylphenoxide.

(b)

Chemical structure of 4-cyanophenoxide.

(c)

Chemical structure of 3-methoxyphenoxide.

Problem 9.37
Predict the product(s) and provide the mechanism for each of the following reactions.

(a)

Reaction equation showing ethyl isopropyl ether reacting with HI (hydroiodic acid). The product is unknown.

(b)

Reaction equation showing ethoxybenzene (phenetole) reacting with HBr (hydrobromic acid). The product is unknown.

Problem 9.38
Predict the product(s) and provide the mechanism for each of the following reactions.

(a)

Tert-butyl ethyl ether reacts with hydrogen bromide to form an unknown product(s), depicted with a question mark.

(b)

Tert-butoxybenzene reacts with hydrogen bromide to form an unknown product(s), depicted with a question mark.

Problem 9.39
Predict the product(s) and provide the mechanism for the following two-step processes.

1-propanol reacts with sodium hydride, then 1-bromopropane to form an unknown product(s), depicted with a question mark.

Problem 9.40
Predict the product(s) and provide the mechanism for the following reaction:

1,2-Epoxy-2-methylcyclohexane reacts with methylmagnesium bromide, then hydronium ion to form an unknown product(s), depicted with a question mark.

Problem 9.41
Fluoxetine, a heavily prescribed antidepressant marketed under the name Prozac, can be prepared by a route that begins with reaction between a phenol and an alkyl chloride.

4-trifluoromethylphenol reacts with an alkyl chloride with phenyl and amine groups in potassium hydroxide and D M S O to produce fluoxetine through a series of steps.

(a) The rate of the reaction depends on both phenol and alkyl halide. Is this an SN1 or an SN2 reaction? Show the mechanism.

(b) The physiologically active enantiomer of fluoxetine has (S) stereochemistry. Based on your answer in part (a), draw the structure of the alkyl chloride you would need, showing the correct stereochemistry.

Problem 9.42
The herbicide acifluorfen can be prepared by a route that begins with reaction between a phenol and an aryl fluoride. Propose a mechanism.

A substituted phenol and sutstituted aryl fluoride react in potassium hydride and dimethyl sulfoxide to yield acifluorfen through a series of steps.

Problem 9.43
Aldehydes and ketones undergo acid-catalyzed reaction with alcohols to yield hemiacetals, from aldehydes or ketals with ketones compounds that have one alcohol-like oxygen and one ether-like oxygen bonded to the same carbon. Further reaction of a hemiacetal with alcohol then yields an acetal, a compound that has two ether-like oxygens bonded to the same carbon.

A carbonyl and R O H react in acid catalyst to produce a hemiacetal; further reaction produces an acetal and water.

(a) Show the structures of the hemiketal and ketal you would obtain by reaction of cyclohexanone with ethanol.

(b) Propose a mechanism for the conversion of a hemiacetal into a ketal.

Naming Alcohols

Problem 9.44
Give IUPAC names for the following compounds:

(a)

Condensed structural formula of a four carbon chain with (counting from left) hydroxyl groups on first and fourth carbons, methyl on third carbon.

(b)

Condensed structural formula of a five carbon chain with (counting from left) hydroxyl group on second carbon, n-propyl group on third carbon.

(c)

Four-carbon ring with wedged hydroxyl and dashed hydrogen on C 1, and dashed hydrogen and wedged hydroxyl on C 3 position.

(d)

Seven-membered ring with hydroxyl (wedge) and hydrogen (dash) on a carbon, methyl (wedge) and hydrogen (dash) on clockwise adjacent carbon, and double bond starting two carbons further clockwise.

(e)

Five-carbon ring with phenyl (wedge) and hydrogen (dash) on a carbon, and hydroxyl (wedge) and hydrogen (dash) two carbons away, clockwise.

(f)

Benzene with hydroxyl on C 1, bromine group on C 2, and cyano group on C 4 position.

Problem 9.45
Draw and name the eight isomeric alcohols with formula C5H12O.

Problem 9.46
Draw structures corresponding to the following IUPAC names:

(a) Trans-3-Chlorocycloheptanol

(b) Ethyl-2-buten-1-ol

(c) o-(2-Hydroxyethyl)phenol

(d) Methyl-1-phenyl-1-butanol

Problem 9.47
Bombykol, the sex pheromone secreted by the female silkworm moth has the formula C16H28O and the systematic name (10E,12Z)-10,12-hexadecadien-1-ol. Draw bombykol, showing the correct geometry for the two double bonds.

Problem 9.48
Carvacrol is a naturally occurring substance isolated from oregano, thyme, and marjoram. What is its IUPAC name?

The structure of carvacrol. It is a benzene with hydroxyl on C 1, methyl on C 2, and isopropyl on C 5.

Naming Ethers, Thiols and Sulfides

Problem 9.49
Draw structures corresponding to the following IUPAC names:

(a) Ethyl 1-ethylpropyl ether

(b) Di(p-chlorophenyl) ether

(c) 3,4-Dimethoxybenzoic acid

(d) Cyclopentyloxycyclohexane

Problem 9.50
Give IUPAC names for the following structures:

(a)

A sulfur atom connected to a cyclohexane group and an isopropyl group.

(b)

A benzene ring with O C H 3 substituents on two adjacent carbons.

(c)

An oxygen atom connected to an isopropyl group and a cyclopropyl group.

(d)

A benzene ring with an S H substituent and, on an adjacent carbon, a nitro group.

(e)

A sulfur with an isopropyl on the right, and a five-carbon chain on the left with methyl groups on (from left) third, fourth, and fifth carbons.

(f)

A central carbon with two methyl and two methoxy substituents.

(g)

A cyclohexane in which one carbon is substituted with two S C H 3 groups.

Synthesizing Alcohols

Problem 9.51
What Grignard reagent and what carbonyl compound might you start with to prepare the following alcohols:

(a)

A four-carbon chain with hydroxyl on C 2 position.

(b)

A five-carbon chain with hydroxyl on C 3 position.

(c)

Chemical structure of 2-methylprop-2-en-1-ol.

(d)

Chemical structure of triphenylmethanol.

(e)

Methanol with two methyl and one phenyl substituents.

(f)

Cyclohexene with C H 2 O H group on C 1 position.

Problem 9.52
What carbonyl compounds would you reduce to prepare the following alcohols: List all possibilities.

(a)

A six-carbon chain with hydroxyl on C 1, and two methyl on C 2 position.

(b)

A three-carbon chain with hydroxyl on C 2 and two methyl groups on C 3 position.

(c)

Chemical structure of 1-cyclohexylpropan-1-ol.

Problem 9.53
What carbonyl compounds might you start with to prepare the following compounds by Grignard reaction? List all possibilities.

(a) 2-Methyl-2-propanol

(b) 1-Ethylcyclohexanol

(c) 3-Phenyl-3-pentanol

(d) 2-Phenyl-2-pentanol

(e)

Benzene with C H 2 C H 2 O H on C 1 and methyl on C 4 position.

(f)

Chemical structure of 1-cyclopentyl-2-methylpropan-2-ol.

Problem 9.54
How would you synthesize the following alcohols, starting with benzene and other alcohols of six or fewer carbons as your only organic reagents?

(a)

The structure having cyclohexanol with ethyl group on C 1.

(b)

Benzyl alcohol with methyl and n-propyl substituents on benzyl carbon.

(c)

A six-carbon chain with hydroxy on C 3 and methyl on C 5 position.

Reactions of Alcohols

Problem 9.55
What products would you obtain from reaction of 1-pentanol with the following reagents:

(a) PBr3

(b) SOCl2

(c) Dess–Martin periodinane

Problem 9.56
How would you prepare the following compounds from 2-phenylethanol: More than one step may be required.

(a) Phenylacetaldehyde (PhCH2CHO)

(b) Phenylacetic acid (PhCH2CO2H)

(c) Ethylbenzene

(d) Bromo-2-phenylethane

Problem 9.57
How would you prepare the following compound from 1-phenylethanol: More than one step may be required.

Acetophenone (PhCOCH3)

Problem 9.58
How would you prepare the following substances from cyclopentanol: More than one step may be required.

(a) Cyclopentanone

(b) Cyclopentene

Problem 9.59
What products would you expect to obtain from reaction of 1-methylcyclohexanol with the following reagents?

(a) NaH

(b) HBr

(c) H2SO4

Synthesizing Ethers

Problem 9.60
How would you prepare the following ethers?

(a)

A central oxygen connected to a benzene ring and an ethyl group.

(b)

A central oxygen connected to a benzene ring and an isopropyl group.

(c)

An oxirane drawn with oxygen on top, wedge hydrogen and dash methyl on left, and wedge methyl and dash hydrogen on right.

(d)

A central oxygen connected to a cyclopentane ring and a t-butyl group.

(e)

A cyclohexane with a wedge methoxy and dash hydrogen on one carbon, and on the adjacent (clockwise) carbon, a wedge hydrogen and dash methoxy.

Problem 9.61
How would you prepare the following compounds from 1-phenylethanol?

(a) Methyl 1-phenylethyl ether

(b) tert-Butyl 1-phenylethyl ether

Problem 9.62
Treatment of trans-2-chlorocyclohexanol with NaOH yields 1,2-epoxycyclohexane, but reaction of the cis isomer under the same conditions yields cyclohexanone. Propose mechanisms for both reactions, and explain why the different results are obtained.

Reactions alter trans-2-chlorocyclohexanol to 1,2-epoxycyclohexane and cis-2-chlorocyclohexanol isomer to cyclohexanone, each utilizing sodium hydroxide and water.

Reactions of Ethers and Epoxides

Problem 9.63
Predict the products of the following ether cleavage reactions:

(a)

Cyclohexyl ethyl ether reacts with hydroiodic acid and water to produce unknown product(s), depicted by a question mark.

(b)

Ethyl vinyl ether reacts with hydroiodic acid and water to produce unknown product(s), depicted by a question mark.

(c)

Ethyl neopentyl ether reacts with hydroiodic acid and water to produce unknown product(s), depicted by a question mark.

Problem 9.64
How would you carry out the following transformation? More than one step may be required.

Cyclohexene reacts with unknown reagent(s) to produce cyclohexyl ethyl ether.

Problem 9.65
What product would you expect from cleavage of tetrahydrofuran with HI?

Problem 9.66
Write the mechanism of the hydrolysis of cis-5,6-epoxydecane by reaction with aqueous acid. What is the stereochemistry of the product, assuming normal backside SN2 attack?

Problem 9.67
What is the stereochemistry of the product from acid-catalyzed hydrolysis of trans-5,6- epoxydecane? How does the product differ from that formed in Problem 18-47?

Problem 9.68
Epoxides are reduced by treatment with lithium aluminum hydride to yield alcohols. Propose a mechanism for this reaction.

Cyclohexene oxide reacts with lithium aluminum hydride in ether, then hydronium, to form cyclohexanol.

General Problems

Problem 9.69
How would you carry out the following transformations?

(a)

Cinnamic acid ((E)-3-phenyl prop-2-enoic acid) reacts with an unknown reagent represented as question mark to form 3-phenylpropanoic acid.

(b)

Cinnamic acid ((E)-3-phenyl prop-2-enoic acid) reacts with an unknown reagent represented as question mark to form trans-3-phenylprop-2-en-1-ol

Problem 9.70
Rank the following substituted phenols in order of increasing acidity, and explain your answer:

The structure of four compounds named phenol, 4-fluorophenol, 4-methoxyphenol and 4-hydroxybenzonitrile.

Problem 9.71
Reaction of (S)-3-methyl-2-pentanone with methylmagnesium bromide followed by acidification yields 2,3-dimethyl-2-pentanol. What is the stereochemistry of the product? Is the product optically active?

The structure of 3-methyl-2-pentanone. It is a five-carbon chain with keto group on C 2 and methyl group on C 3.

Problem 9.72
As a rule, axial alcohols oxidize somewhat faster than equatorial alcohols. Which would you expect to oxidize faster, cis-4-tert-butylcyclohexanol or trans-4-tert-butylcyclohexanol? Draw the more stable chair conformation of each molecule.

Problem 9.73
A problem often encountered in the oxidation of primary alcohols to carboxylic acids is that esters are sometimes produced as by-products. For example, oxidation of ethanol yields acetic acid and ethyl acetate:

Ethanol reacts with chromium trioxide to form acetic acid and ethylacetate.

Propose a mechanism to account for the formation of ethyl acetate. Take into account the reversible reaction between aldehydes and alcohols:

An aldehyde, R C H O reacts with R dash O H to form carbon linked to H , R, O H and O R dash group.

Problem 9.74
Identify the reagents a–f in the following scheme:

Cyclohexanol reacts with reagent a to form cyclohexanol. b to form cyclohexylbromide. c to form cyclohexylmethanol. d to form cyclohexanecarbaldehyde, e to form 1-cyclohexyl-2-phenylethanol, f to form (E)-(2-cyclohexylvinyl)benzene.

Problem 9.75
Predict the products of the following reactions:

(a)

Isobutyl phenyl ether reacts with hydrogen bromide to form an unknown product(s) depicted by a question mark.

Problem 9.76
Grignard reagents react with oxetane, a four-membered cyclic ether, to yield primary alcohols, but the reaction is much slower than the corresponding reaction with ethylene oxide. Suggest a reason for the difference in reactivity between oxetane and ethylene oxide.

Oxetane (four-membered ring incorporating one oxygen) reacts with R Mg X, then hydronium, to produce R C H 2 C H 2 C H 2 O H.

Problem 9.77
The Zeisel method is an old analytical procedure for determining the number of methoxyl groups in a compound. A weighed amount of the compound is heated with concentrated HI, ether cleavage occurs, and the iodomethane product is distilled off and passed into an alcohol solution of AgNO3, where it reacts to form a precipitate of silver iodide. The AgI is then collected and weighed, and the percentage of methoxyl groups in the sample is thereby determined. For example, 1.06 g of vanillin, the material responsible for the characteristic odor of vanilla, yields 1.60 g of AgI. If vanillin has a molecular weight of 152, how many methoxyl groups does it contain?

Problem 9.78
Identify the reagents a–e in the following scheme:

Cyclohexanone is transformed into 1-methylcyclohexanol by reagent a; b and c convert 1-methylcyclohexanol to 1-methylcyclohexene and 1-methyl-1-methoxycyclohexane respectively. D converts 1-methylcyclohexene into 1,2-epoxy-1-methylcyclohexane, which is converted by e into (1S,2S)-1-methylcyclohexan-1,2-diol.

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