17.16: Additional Problems
- Page ID
- 459829
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Visualizing Chemistry
Give IUPAC names for the following compounds:
(a) (b)
(c) (d)
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)
Predict the product from the reaction of the following substance (reddish brown = Br) with:
Predict the product from reaction of the following substance with:
(a) NaBH4; then H3O+ (b) LiAlH4; then H3O+ (c) 2 CH3CH2MgBr; then H3O+
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
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.
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.
Epoxides react with Grignard reagents to yield alcohols. Propose a mechanism.
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.
Reduction of 2-butanone with NaBH4 yields 2-butanol. Is the product chiral? Is it optically active? Explain.
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)Identify the type of substitution mechanism (SN1, SN2) involved in the conversion of the following alcohols into the corresponding alkyl halide.
(a) (b)
(c)
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)
(b)
c)
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)
(b)
(c)
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)
(c) triethylsilyl chloride (TES-Cl)
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.
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) (b)
(c)
Naming Alcohols
Give IUPAC names for the following compounds:
(a) <p">(e) (f)
Draw and name the eight isomeric alcohols with formula C5H12O.
Draw structures corresponding to the following IUPAC names:
(a) Trans-3-Chlorocycloheptanol
(b) 2-Ethyl-2-buten-1-ol
(c) o-(2-Hydroxyethyl)phenol
(d) 3-Methyl-1-phenyl-1-butanol
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.
Carvacrol is a naturally occurring substance isolated from oregano, thyme, and marjoram. What is its IUPAC name?
Synthesizing Alcohols
What Grignard reagent and what carbonyl compound might you start with to prepare the following alcohols:
(a) (b)
(c)
(d) (e)
(f)
What carbonyl compounds would you reduce to prepare the following alcohols: List all possibilities.
(a)
(b)
(c)
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) (f)
How would you synthesize the following alcohols, starting with benzene and other alcohols of six or fewer carbons as your only organic reagents?
(a)Reactions of Alcohols
What products would you obtain from reaction of 1-pentanol with the following reagents:
(a) PBr3 (b) SOCl2 (c) Dess–Martin periodinane
How would you prepare the following compounds from 2-phenylethanol: More than one step may be required.
(a) Styrene (PhCHCH2)(b) Phenylacetaldehyde (PhCH2CHO) (c) Phenylacetic acid (PhCH2CO2H) (d) Benzoic acid (e) Ethylbenzene (f) Benzaldehyde (g) 1-Phenylethanol (h) 1-Bromo-2-phenylethane
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
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
What products would you expect to obtain from the reaction of 1-methylcyclohexanol with the following reagents?
(a) HBr (b) NaH (c) H2SO4
Spectroscopy
The following 1H NMR spectrum is that of an alcohol, C8H10O. Propose a structure.
(b) C8H10O
Propose a structure consistent with the following spectral data for a compound C8H18O2:
- IR: 3350 cm–1
- 1H NMR: 1.24 δ (12 H, singlet); 1.56 δ (4 H, singlet); 1.95 δ (2 H, singlet)
The 1H NMR spectrum shown is that of 3-methyl-3-buten-1-ol. Assign all the observed resonance peaks to specific protons, and account for the splitting patterns.
A compound of unknown structure gave the following spectroscopic data:
- Mass spectrum: M+ = 88.1
- IR: 3600 cm–1
- 1H NMR: 1.4 δ (2 H, quartet, J = 7 Hz); 1.2 δ (6 H, singlet); 1.0 δ (1 H, singlet); 0.9 δ (3 H, triplet, J = 7 Hz)
- 13C NMR: 74, 35, 27, 25 δ
(a) Assuming that the compound contains C and H but may or may not contain O, give three possible molecular formulas.
(b) How many hydrogens does the compound contain?
(c) What functional group(s) does the compound contain?
(d) How many carbons does the compound contain?
(e) What is the molecular formula of the compound?
(f) What is the structure of the compound?
(g) Assign peaks in the molecule’s 1H NMR spectrum corresponding to specific protons.
Propose a structure for a compound C15H24O that has the following 1H NMR spectrum. The peak marked by an asterisk disappears when D2O is added to the sample.
General Problems
How would you carry out the following transformations?
(a)
(b)
(c)
Benzoquinone is an excellent dienophile in the Diels–Alder reaction. What product would you expect from reaction of benzoquinone with 1 equivalent of 1,3-butadiene? From reaction with 2 equivalents of 1,3-butadiene?
Rank the following substituted phenols in order of increasing acidity, and explain your answer:>
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 SN2 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.
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?
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.
Starting from testosterone (Problem 17-62), how would you prepare the following substances?
(a)
(b)
(c)
(d)
p-Nitrophenol and 2,6-dimethyl-4-nitrophenol both have pKa = 7.15, but 3,5-dimethyl-4-nitrophenol has pKa = 8.25. Why is 3,5-dimethyl-4-nitrophenol so much less acidic?
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.
Compound A, C5H10O, is one of the basic building blocks of nature. All steroids and many other naturally occurring compounds are built from compound A. Spectroscopic analysis of A yields the following information:
- IR: 3400 cm–1; 1640 cm–1
- 1H NMR: 1.63 δ (3 H, singlet); 1.70 δ (3 H, singlet); 3.83 δ (1 H, broad singlet); 4.15 δ (2 H, doublet, J = 7 Hz); 5.70 δ (1 H, triplet, J = 7 Hz)
- (a) How many double bonds and/or rings does A have?
- (b) From the IR spectrum, what is the identity of the oxygen-containing functional group?
- (c) What kinds of hydrogens are responsible for the NMR absorptions listed?
- (d) Propose a structure for A.
Dehydration of trans-2-methylcyclopentanol with POCl3 in pyridine yields predominantly 3-methylcyclopentene. Is the stereochemistry of this dehydration syn or anti?
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.
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.
Propose a synthesis of bicyclohexylidene, starting from cyclohexanone as the only source of carbon.
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:
Propose a mechanism to account for the formation of ethyl acetate. Take into account the reversible reaction between aldehydes and alcohols:
Identify the reagents a–f in the following scheme:
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.
Propose structures for alcohols that have the following <sup">1H NMR spectra:
(a) C9H12O
(b) C8H10O2
Compound A, C8H10O, has the IR and 1H NMR spectra shown. Propose a structure consistent with the observed spectra, and label each peak in the NMR spectrum. Note that the absorption at 5.5 δ disappears when D2O is added.