12.B: Additional Problems

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Sol Parajon Puenzo
Cañada College

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Visualizing Chemistry

PROBLEM 12-20 Give IUPAC names for the following compounds:

(a) (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 12-21 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) (b) A ball-and-stick model of five carbon chain with hydroxyl on C 1, and methyl group on C 3 position.

PROBLEM 12-22 Predict the product from the 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 (e) Br₂, FeBr₃

PROBLEM 12-25 Predict the product from reaction of the following substance with:

(a) NaBH₄; then H₃O⁺ (b) LiAlH₄; then H₃O⁺ (c) 2 CH₃CH₂MgBr; then H₃O⁺

PROBLEM 12-24 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.

Mechanism Problems

PROBLEM 12-25 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=

PROBLEM 12-26 Acid-catalyzed dehydration of 2,2-dimethylcyclohexanol yields a mixture of 1,2-dimethylcyclohexene and isopropylidenecyclopentane. Propose a mechanism to account for the formation of both products.

the=

PROBLEM 12-27 Epoxides react with Grignard reagents to yield alcohols. Propose a mechanism.

cyclopentane=

PROBLEM 12-28 Treatment of the following epoxide with aqueous acid produces a carbocation intermediate that reacts with water to give a diol product. Show the structure of the carbocation, and propose a mechanism for the second step.

an=

PROBLEM 12-29 Reduction of 2-butanone with NaBH₄ yields 2-butanol. Is the product chiral? Is it optically active? Explain.

PROBLEM 12-30 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= (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 12-31 Identify the type of substitution mechanism (S_N1, S_N2) involved in the conversion of the following alcohols into the corresponding alkyl halide.

(a) 2-methylbutan-2-ol= (b) 2-butanol reacts with P Br 3 to form 2-bromobutane.

PROBLEM 12-32 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) 1-methylcyclohexanol reacts with hydronium to form 1-methylcyclohexene.

(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 12-33 For each reaction, draw the complete mechanism using curved arrows. For each reaction, write the mechanism using curved arrows for the conversion of the alcohol into the corresponding alkene with POCl₃. In each case, explain the regiochemistry of the elimination.

(a) Cyclohexane with dashed bond to isopropyl, wedged bond to hydroxyl on adjacent (clockwise) carbon reacts with phosphoryl chloride to form R-3-isopropylcyclohexene.

(b) 3-methyl-2-pentanol reacts with P O Cl 3 in pyridine to produce E-3-methyl-2-pentene.

PROBLEM 12-34 The trimethylsilyl (TMS) protecting group is one of several silicon-protecting groups for alcohols. For each reaction, draw the mechanism for the protection of (R)-3-bromo-1-butanol with the following silyl chlorides, using triethylamine as the base:

(a) tert-butyldimethylsilyl chloride (TBS-Cl)

(b) triisopropylsilyl chloride (TIPS-Cl)

PROBLEM 12-35 When the following alcohol is treated with POCl₃ and pyridine, the expected elimination product is formed. However, when the same alcohol is treated with H₂SO₄, the elimination product is 1,2-dimethylcyclopentene. Propose a mechanism for each pathway to account for these differences.

propan-2-ylidenecyclobutane=

PROBLEM 12-36 Phenols generally have lower pK_a’s than alcohols because of resonance stabilization with the aromatic ring. Draw all of the resonance contributors for the following phenolate ions.

(a) chemical= (b) Chemical structure of 4-cyanophenoxide. (c) Chemical structure of 3-methoxyphenoxide.

Naming Alcohols

PROBLEM 12-37 Give IUPAC names for the following compounds:

(a) condensed= (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 12-38 Draw and name the eight isomeric alcohols with formula C₅H₁₂O.

PROBLEM 12-39 Draw structures corresponding to the following IUPAC names:

(a) Trans-3-Chlorocycloheptanol

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

(d) 3-Methyl-1-phenyl-1-butanol

PROBLEM 12-40 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 12-41 Carvacrol is a naturally occurring substance isolated from oregano, thyme, and marjoram. What is its IUPAC name?

the=

Synthesizing Alcohols

PROBLEM 12-42 What Grignard reagent and what carbonyl compound might you start with to prepare the following alcohols:

(a) (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 12-43 What carbonyl compounds would you reduce to prepare the following alcohols: List all possibilities.

(a) (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 12-44 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

(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 12-45 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= (b) A six-carbon chain with hydroxy on C 1 and methyl group on C 3 position. (c) Benzyl alcohol with methyl and n-propyl substituents on benzyl carbon. (d)

Reactions of Alcohols

PROBLEM 12-46 What products would you obtain from reaction of 1-pentanol with the following reagents:

(a) PBr₃ (b) SOCl₂ (c) Dess–Martin periodinane

PROBLEM 12-47 How would you prepare the following compounds from 2-phenylethanol: More than one step may be required.

(a) Styrene (PhCH $\text{=$ CH₂) (b) Phenylacetaldehyde (PhCH₂CHO) (c) Phenylacetic acid (PhCH₂CO₂H) (d) Benzoic acid

(e) Ethylbenzene (f) Benzaldehyde (g) 1-Phenylethanol (h) 1-Bromo-2-phenylethane

PROBLEM 12-48 How would you prepare the following compounds from 1-phenylethanol: More than one step may be required.

(a) Acetophenone (PhCOCH₃) (b) Benzyl alcohol (c) m-Bromobenzoic acid (d) 2-Phenyl-2-propanol

PROBLEM 12-49 How would you prepare the following substances from cyclopentanol: More than one step may be required.

(a) Cyclopentanone (b) Cyclopentene (c) 1-Methylcyclopentanol (d) trans-2-Methylcyclopentanol

PROBLEM 12-50 What products would you expect to obtain from the reaction of 1-methylcyclohexanol with the following reagents?

(a) HBr (b) NaH (c) H₂SO₄

General Problems

PROBLEM 12-51 How would you carry out the following transformations?

(a) cinnamic=

(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

(c) 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-thiol

PROBLEM 12-52 Removed

PROBLEM 12-53 Rank the following substituted phenols in order of increasing acidity, and explain your answer:

the=

PROBLEM 12-54 Benzyl chloride can be converted into benzaldehyde by treatment with nitromethane and base. The reaction involves initial conversion of nitromethane into its anion, followed by S_N2 reaction of the anion with benzyl chloride and subsequent E2 reaction. Write the mechanism in detail, using curved arrows to indicate the electron flow in each step.

benzyl=

PROBLEM 12-55 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=

PROBLEM 12-56 Testosterone is one of the most important male steroid hormones. When testosterone is dehydrated by treatment with acid, rearrangement occurs to yield the product shown. Propose a mechanism to account for this reaction.

testosterone=

PROBLEM 12-57 Starting from testosterone (Exercise $\PageIndex{56}$), how would you prepare the following substances?

(a) cyclopentanone= (b) Cyclopentane with wedged hydroxyl, dashed hydrogen fused to cyclohexane with wedged methyl, dashed hydrogen. This is connected to cyclohexane with wedged hydrogen and methyl, dashed hydrogen, bonded to cyclohexene.

(c) Cyclopentanone fused to cyclohexane with wedged methyl, dashed hydrogen. This is connected to cyclohexane with wedged hydrogen and methyl, dashed hydrogen. This is bonded to cyclohexanone. (d) Cyclopentane with wedged hydroxyl, dashed hydrogen fused to cyclohexane with wedged methyl, dashed hydrogen. This is connected to cyclohexane with wedged hydrogen and methyl, dashed hydrogen, bonded to cyclohexane.

PROBLEM 12-58 p-Nitrophenol and 2,6-dimethyl-4-nitrophenol both have pK_a = 7.15, but 3,5-dimethyl-4-nitrophenol has pK_a = 8.25. Why is 3,5-dimethyl-4-nitrophenol so much less acidic?

The structure of 4-nitrophenol, 2,6-dimethyl-4-nitrophenol, and 3,5-dimethyl-4-nitrophenol with p K a values 7.15, 7.15, and 8.25, respectively.

PROBLEM 12-59 Compound A, C₁₀H₁₈O, undergoes reaction with dilute H₂SO₄ at 25 °C to yield a mixture of two alkenes, C₁₀H₁₆. The major alkene product, B, gives only cyclopentanone after ozone treatment followed by reduction with zinc in acetic acid. Write the reactions involved, and identify A and B.

PROBLEM 12-60 Dehydration of trans-2-methylcyclopentanol with POCl₃ in pyridine yields predominantly 3-methylcyclopentene. Is the stereochemistry of this dehydration syn or anti?

PROBLEM 12-61 2,3-Dimethyl-2,3-butanediol has the common name pinacol. On heating with aqueous acid, pinacol rearranges to pinacolone, 3,3-dimethyl-2-butanone. Suggest a mechanism for this reaction.

pinacol=

PROBLEM 12-62 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 12-63 Removed

PROBLEM 12-64 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=

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 12-65 Identify the reagents a–f in the following scheme:

cyclohexanol=

PROBLEM 12-66 Galactose, a constituent of the disaccharide lactose found in dairy products, is metabolized by a pathway that includes the isomerization of UDP-galactose to UDP-glucose, where UDP = uridylyl diphosphate. The enzyme responsible for the transformation uses NAD⁺ as cofactor. Propose a mechanism.

the=

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