820
Chapter 17
Aldehydes and Ketones
27. The following spectroscopic data are for two carbonyl compounds with the formula C8H12O.
Suggest a structure for each compound. The letter “m” stands for the appearance of this particular
part of the spectrum as an uninterpretable multiplet. (a) 1H NMR: d 5 1.60 (m, 4 H), 2.15 (s, 3 H),
2.19 (m, 4 H), and 6.78 (t, 1 H) ppm. 13C NMR: d 5 21.8, 22.2, 23.2, 25.0, 26.2, 139.8, 140.7,
and 198.6 ppm. (b) 1H NMR: d 5 0.94 (t, 3 H), 1.48 (sex, 2 H), 2.21 (q, 2 H), 5.8 – 7.1
(m, 4 H), and 9.56 (d, 1 H) ppm. 13C NMR: d 5 13.6, 21.9, 35.2, 129.0, 135.2, 146.7, 152.5,
and 193.2 ppm.
28. The compounds described in Problem 27 have very different ultraviolet spectra. One has
lmax(e) 5 232(13,000) and 308(1450) nm, whereas the other has lmax(e) 5 272(35,000) nm and
a weaker absorption near 320 nm (this value is hard to determine accurately because of the
intensity of the stronger absorption). Match the structures that you determined in Problem 27 to
these UV spectral data. Explain the spectra in terms of the structures.
29. Following are spectroscopic and analytical characteristics for an unknown compound. Propose a
structure. Empirical formula: C8H16O. 1H NMR: d 5 0.90 (t, 3 H), 1.0–1.6 (m, 8 H), 2.05 (s, 3 H),
and 2.25 (t, 2 H) ppm. IR: 1715 cm21. UV: lmax(e) 5 280(15) nm. MS: myz 5 128 (M1• );
intensity of (M 1 1)1 peak is 9% of M1• peak; important fragments are at myz 5 113 (M 2 15)1
myz 5 85 (M 2 43)1, myz 5 71 (M 2 57)1, myz 5 58 (M 2 70)1 (the second largest peak),
and myz 5 43 (M 2 85)1 (the base peak).
30. Reaction review. Without consulting the Reaction Road Map on pp. 816 –817, suggest reagents
to convert each of the starting materials below into 3-hexanone.
OH
(b)
(a)
O
O
(c)
S
N
S
N
(d)
(e)
(g)
(h)
(f )
HO
CN
31. Indicate which reagent or combination of reagents is best suited for each of the following
reactions.
OH
O
O
(c)
O
B
CH3CCH2CH2CH2CHO
H
OH
(b)
(a)
O
(d)
O
(f )
(e)
O
32. Write the expected products of ozonolysis (followed by mild reduction—e.g., by Zn) of each of
the following molecules.
(a) CH3CH2CH2CHPCH2
(b)
(c)
(d)
Chapter 17
Problems
33. For each of the following groups, rank the molecules in decreasing order of reactivity toward
addition of a nucleophile to the most electrophilic sp2-hybridized carbon.
OOO
O
OO
B
BB
BBB
(b) CH3CCH3, CH3CCCH3, CH3CCCCH3
1
(a) (CH3)2CPO, (CH3)2CPNH, (CH3)2CPO H
(c) BrCH2COCH3, CH3COCH3, CH3CHO, BrCH2CHO
34. Give the expected products of reaction of butanal with each of the following reagents.
(a) LiAlH4, (CH3CH2)2O, then H1, H2O
(b) CH3CH2MgBr, (CH3CH2)2O, then H1, H2O
(c) HOCH2CH2OH, H1
35. Give the expected products of reaction of 2-pentanone with each of the reagents in Problem 34.
36. Give the expected products of reaction of 4-acetylcyclohexene with each of the reagents in
Problem 34.
37. Give the expected product(s) of each of the following reactions.
O
O
⫹ excess CH3OH
(a)
⫺
OH
⫹ excess CH3OH
(b)
H⫹
O
O
CH3
(c)
⫹ H3C
S
OH
O
NHNH2
H⫹
(d) CH3CCH3 ⫹ HOCH2CHCH2CH2CH3
O
O
CH3
%
⫹ 2 CH3CH2SH
(e)
BF3, (CH3CH2)2O
(f )
⫹ (CH3CH2)2NH
O
38. Formulate detailed mechanisms for (a) the formation of the hemiacetal of acetaldehyde and
methanol under both acid- and base-catalyzed conditions and (b) the formation of the intramolecular hemiacetal of 5-hydroxypentanal (Section 17-7), again under both acid- and base-catalyzed
conditions.
39. Formulate the mechanism of the BF3-catalyzed reaction of CH3SH with butanal (Section 17-8).
40.
Overoxidation of primary alcohols to carboxylic acids is caused by the water present in the usual aqueous acidic Cr(VI) reagents. The water adds to the initial aldehyde product
to form a hydrate, which is further oxidized (Section 17-6). In view of these facts, explain the
following two observations. (a) Water adds to ketones to form hydrates, but no overoxidation
follows the conversion of a secondary alcohol into a ketone. (b) Successful oxidation of primary
alcohols to aldehydes by the water-free PCC reagent requires that the alcohol be added slowly
to the Cr(VI) reagent. If, instead, the PCC is added to the alcohol, a new side reaction forms an
ester. This is illustrated for 1-butanol.
O
B
CH3CH2CH2CH2OH uuuvvy CH3CH2CH2COCH2CH2CH2CH3
PPC, CH2Cl2
(c) Give the products expected from reaction of 3-phenyl-1-propanol and water-free CrO3
(1) when the alcohol is added to the oxidizing agent and (2) when the oxidant is added to the
alcohol.
H⫹
821
822
Chapter 17
Aldehydes and Ketones
41. Explain the results of the following reactions by means of mechanisms.
ðOð
š
Oð š
ðOH
H⫹
O
š
(a) HO
O
O
H⫹
O
OH
(b) HO
(c) Explain why hemiacetal formation may be catalyzed by either acid or base, but acetal formation is catalyzed only by acid, not by base.
42. The two isomeric compounds below are naturally occurring insect pheromones. The isomer on
the left attracts the male olive fruit fly; the one on the right, the female. (a) What kind of isomeric
relationship exists between these two structures? (b) What functional group is contained in these
molecules? (c) Both of these compounds are hydrolyzed under aqueous acidic conditions. Draw
the products. Are the product molecules from the two starting isomers the same or different?
O
O
O
⫺
O
A
⫹
N
CH2OH
⫹N
CH3
A
⫺
O
O
43. Formulate a plausible mechanism for the following reaction. The product is a precursor of mediquox
(shown in the margin), an agent used to treat respiratory infections in chickens (no, we are not
making this up).
NH2
⫹
Mediquox
H3C
NH2
O
B
C
G
Benzene-1,2-diamine
GC G
B
O
CH3
N
CH3
N
CH3
CH3CH2OH
2,3-Dimethylquinoxaline
44. The formation of imines, oximes, hydrazones, and related derivatives from carbonyl compounds
is reversible. Write a detailed mechanism for the acid-catalyzed hydrolysis of cyclohexanone
semicarbazone to cyclohexanone and semicarbazide.
N
O
B
NHCNH2
D
O
⫹
H2O
H⫹
⫹
O
B
NH2NHCNH2
45. Reaction review II. Without consulting the Reaction Road Map on p. 818, suggest reagents to
convert cyclohexanone into each of the compounds below.
OH
S
(b)
(a)
O
HO
S
CH2CH3
HO
(c)
(d)
(g)
(h)
N(CH2CH3)2
O
(e)
(f)
CN
Chapter 17
Problems
CH3O
OCH3
N
HO
(i)
(j)
(k)
(l)
46. Propose reasonable syntheses of each of the following molecules, beginning with the indicated
starting material.
HO
(a)
OH
O
BB
from
OH
(b) C6H5NPC(CH2CH3)2 from 3-pentanol
OH
(c)
from 1,5-pentanediol
HO
O
(d)
from
O
OH
47. The UV absorptions and colors of 2,4-dinitrophenylhydrazone derivatives of aldehydes and
ketones depend sensitively on the structure of the carbonyl compound. Suppose that you are asked
to identify the contents of three bottles whose labels have fallen off. The labels indicate that one
bottle contained butanal, one contained trans-2-butenal, and one contained trans-3-phenyl-2propenal. The 2,4-dinitrophenylhydrazones prepared from the contents of the bottles have the
following characteristics.
Bottle 1: m.p. 187 – 1888C; lmax 5 377 nm; orange color
Bottle 2: m.p. 121 – 1228C; lmax 5 358 nm; yellow color
Bottle 3: m.p. 252 – 2538C, lmax 5 394 nm; red color
Match up the hydrazones with the aldehydes (without first looking up the melting points of these
derivatives), and explain your choices. (Hint: See Section 14-11.)
48. Indicate the reagent(s) best suited to effect these transformations.
O
(a)
O
O
B
(b) CH3CH P CHCH2CH2CH
O
B
CH3CH2CH2CH2CH2CH
O
B
(c) CH3CH P CHCH2CH2CH
CH3CH P CHCH2CH2CH2OH
%
-OH
%
(d)
]OH
O
O
49. The molecule bombykol, whose structure is shown below, is a powerful insect pheromone, the
sex attractant of the female silk moth (see Section 12-17). It was initially isolated in the amount
of 12 mg from extraction of 2 tons of moth pupae. Propose a synthesis of bombykol from two
simpler molecules based on the Wittig reaction.
CH3CH2CH2CPCCHPCH(CH2)8CO2CH2CH3
Bombykol
O
823
824
Chapter 17
Aldehydes and Ketones
50. For each of the following molecules, propose two methods of synthesis from the different precursor molecules indicated.
(a) CH3CHPCHCH2CH(CH3)2 from (1) an aldehyde and (2) a different aldehyde
CH3
(b)
from (1) a dialdehyde and (2) a diketone
CH3
51. Three isomeric ketones with the molecular formula C7H14O are converted into heptane by
Clemmensen reduction. Compound A gives a single product upon Baeyer-Villiger oxidation;
compound B gives two different products in very different yields; compound C gives two different
products in virtually a 1 : 1 ratio. Identify A, B, and C.
52. Give the product(s) of reaction of hexanal with each of the following reagents.
(a) HOCH2CH2OH, H1
(b) LiAlH4, then H1, H2O
(c) NH2OH, H1
(d) NH2NH2, KOH, heat
(e) (CH3)2CHCH2CHPP(C6H5)3
(f)
N
H
(g) Ag1, NH3, H2O
(h) CrO3, H2SO4, H2O
, H⫹
(i) HCN
53. Give the product(s) of reaction of cycloheptanone with each of the reagents in Problem 52.
54. Formulate in full detail the mechanism for the Wolff-Kishner reduction of 1-phenylethanone
(acetophenone) to ethylbenzene (see p. 803).
55. The general equation for the Baeyer-Villiger oxidation (see p. 808) begins with a reaction between
a ketone and a peroxycarboxylic acid to form a peroxy analog of a hemiacetal. Formulate a
detailed mechanism for this process.
O
56. Formulate a detailed mechanism for the Baeyer-Villiger oxidation of the ketone shown in the
margin (refer to Exercise 17-22).
57. Give the two theoretically possible Baeyer-Villiger products from each of the following compounds. Indicate which one is formed preferentially.
(a)
O
r
CO
O
CH3
O
CH3
(b)
O
(c)
(d)
O
B
(e) C6H5CCH3
H
58. Propose efficient syntheses of each of the following molecules, beginning with the indicated
starting materials.
CHO
from
(a)
H3C
O
(c)
OH
O
CHO
(b)
H
OH
OH
CH3
from ClCH2CH2CH2OH
rC f
CH3
CHO
from
H
OH
Problems
59.
Explain the fact that, although hemiacetal formation between methanol and cyclohexanone is thermodynamically disfavored, addition of methanol to cyclopropanone goes essentially
to completion:
O
HO
OCH3
⫹ CH3OH
60. The rate of the reaction of NH2OH with aldehydes and ketones is very sensitive to pH. It is very
low in solutions more acidic than pH 2 or more basic than pH 7. It is highest in moderately acidic
solution (pH , 4). Suggest explanations for these observations.
61. Compound D, formula C8H14O, is converted by CH2PP(C6H5)3 into compound E, C9H16. Treatment
of compound D with LiAlH4 yields two isomeric products F and G, both C8H16O, in unequal yield.
Heating either F or G with concentrated H2SO4 produces H, with the formula C8H14. Ozonolysis of
H produces a ketoaldehyde after Zn–H1, H2O treatment. Oxidation of this ketoaldehyde with aqueous Cr(VI) produces
O
CO2H
Identify compounds D through H. Pay particular attention to the stereochemistry of D.
62. In 1862, it was discovered that cholesterol (for structure, see Section 4-7) is converted into a new
substance named coprostanol by the action of bacteria in the human digestive tract. Make use of the
following information to deduce the structure of coprostanol. Identify the structures of unknowns
J through M as well. (i) Coprostanol, upon treatment with Cr(VI) reagents, gives compound J,
UV lmax(e) 5 281(22) nm and IR 5 1710 cm21. (ii) Exposure of cholesterol to H2 over Pt results
in compound K, a stereoisomer of coprostanol. Treatment of K with the Cr(VI) reagent furnishes
compound L, which has a UV peak very similar to that of compound J, lmax(e) 5 258(23) nm,
and turns out to be a stereoisomer of J. (iii) Careful addition of Cr(VI) reagent to cholesterol
produces M: UV lmax(e) 5 286(109) nm. Catalytic hydrogenation of M over Pt also gives L.
63.
Three reactions that include compound M (see Problem 62) are described here.
Answer the questions that follow. (a) Treatment of M with catalytic amounts of acid in ethanol
solvent causes isomerization to compound N: UV lmax(e) 5 241(17,500) and 310(72) nm. Propose
a structure for N. (b) Hydrogenation of compound N (H2–Pd, ether solvent) produces compound J
(Problem 62). Is this the result that you would have predicted, or is there something unusual
about it? (c) Wolff-Kishner reduction of compound N (H2NNH2, H2O, HO2, D) leads to 3-cholestene.
Propose a mechanism for this transformation.
H
/ CH3
CH3 ∑
% $
CH3
%
CH3
CH3
H
%
≥
H
3-Cholestene
Team Problem
64. In acidic methanol, 3-oxobutanal is transformed into a compound with the molecular formula
C6H12O3.
O
O
CH3OH, H⫹
H
C6H12O3
3-Oxobutanal
As a group, analyze the following 1H NMR and IR spectral data: 1H NMR (CCl4): d 5 2.19
(s, 3 H), 2.75 (d, 2 H), 3.38 (s, 6 H), 4.89 (t, 1 H) ppm; IR: 1715 cm21.
Chapter 17
825
826
Chapter 17
Aldehydes and Ketones
Consider the chemical shifts, the splitting patterns, and the integrations of the signals in the
NMR spectrum and discuss possible fragments that could give rise to the observed multiplicities.
Use the IR information to assign the functional group that exists in the new molecule. Present an
explanation for your structural determination, including reference to the spectral data, and suggest
a detailed mechanism for the formation of the new compound.
Preprofessional Problems
65. In the transformation shown here, which of the following compounds is most likely to be
compound A (use IUPAC name)? (a) 5-Octyn-7-one; (b) 5-octyn-2-one; (c) 3-octyn-2-one;
(d) 2-octyn-3-one.
CrO , H SO , acetone
3
2
4
3-Octyn-2-ol uuuuvvu
uvy A
O
B
66. The reaction
CO
H 3C O H
CH2 P C
f
H
i
demonstrates (a) resonance;
OH
(b) tautomerism; (c) conjugation; (d) deshielding.
67. Which of the following reagents converts benzenecarbaldehyde (benzaldehyde) into an oxime?
(a) H2NNHC6H5; (b) H2NNH2; (c) O3; (d) H2NOH; (e) CH3CH(OH)2.
68. Which of the following statements is correct? In the IR spectrum of 3-methyl-2-butanone, the most
intense absorption is at (a) 3400 cm21, owing to an OH stretching mode; (b) 1700 cm21, owing
to a CPO stretching mode; (c) 2000 cm21, owing to a CH stretching mode; (d) 1500 cm21,
owing to the rocking of an isopropyl group.