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Chapter 19: Aldehydes and Ketones: Nucleophilic Addition Reactions

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Chapter 19: Aldehydes and Ketones: Nucleophilic Addition Reactions

26 problems · 39 figures

19-1 §19.1 source ↗

Name the following aldehydes and ketones:
(a)
(b)
(c)
(d)
(e)
(f)

Answer (6 parts)

(a)
2-Methyl-3-pentanone
(b)
3-Phenylpropanal
(c)
2,6-Octanedione
(d)
trans-2-Methylcyclohexanecarbaldehyde
(e)
4-Hexenal
(f)
cis-2,5-Dimethylcyclohexanone

19-2 §19.1 source ↗

Draw structures corresponding to the following names:
(a)
3-Methylbutanal
(b)
4-Chloro-2-pentanone
(c)
Phenylacetaldehyde
(d)
cis-3-tert-Butylcyclohexanecarbaldehyde
(e)
3-Methyl-3-butenal
(f)
2-(1-Chloroethyl)-5-methylheptanal

Answer (6 parts)

(a)
(b)
(c)
(d)
(e)
(f)

19-3 §19.2 source ↗

How would you prepare pentanal from the following starting materials?
(a)
CH3CH2CH2CH2CH2OH
(b)
CH3CH2CH2CH2CH = CH2
(c)
CH3CH2CH2CH2CO2CH3
(d)
CH3CH2CH2CH = CH2

Answer (4 parts)

(a)
Dess–Martin periodinane
(b)
1. O3; 2. Zn
(c)
DIBAH
(d)
1. BH3, then H2O2, NaOH; 2. Dess–Martin periodinane

19-4 §19.2 source ↗

How would you carry out the following reactions? More than one step may be needed.
(a)
3-Hexyne → 3-Hexanone
(b)
Benzene → m-Bromoacetophenone
(c)
Bromobenzene → Acetophenone
(d)
1-Methylcyclohexene → 2-Methylcyclohexanone

Answer (4 parts)

(a)
HgSO4, H3O+
(b)
1. CH3COCl, AlCl3; 2. Br2, FeBr3
(c)
1. Mg; 2. CH3CHO; 3. H3O+; 4. CrO3
(d)
1. BH3; 2. H2O2, NaOH; 3. CrO3

19-5 §19.4 source ↗

Treatment of an aldehyde or ketone with cyanide ion (−:C ≡ N), followed by protonation of the tetrahedral alkoxide ion intermediate, gives a cyanohydrin. Show the structure of the cyanohydrin obtained from cyclohexanone.

Answer

19-6 §19.4 source ↗

p-Nitrobenzaldehyde is more reactive toward nucleophilic additions than p-methoxybenzaldehyde. Explain.

Answer

The electron-withdrawing nitro group in p-nitrobenzaldehyde polarizes the carbonyl group.

19-7 §19.5 source ↗

When dissolved in water, trichloroacetaldehyde exists primarily as its hydrate, called chloral hydrate. Show the structure of chloral hydrate.

Answer

CCl3CH(OH)2

19-8 §19.5 source ↗

The oxygen in water is primarily (99.8%) 16O, but water enriched with the heavy isotope 18O is also available. When an aldehyde or ketone is dissolved in 18O-enriched water, the isotopic label becomes incorporated into the carbonyl group. Explain.

R2C = O + H2O ⇌ R2C = O + H2O    where O = 18O

Answer

Labeled water adds reversibly to the carbonyl group.

19-9 §19.6 source ↗

Cyclohexanone forms a cyanohydrin in good yield but 2,2,6-trimethylcyclohexanone does not. Explain.

Answer

The equilibrium is unfavorable for sterically hindered ketones.

19-10 §19.8 source ↗

Show the products you would obtain by acid-catalyzed reaction of cyclohexanone with ethylamine, CH3CH2NH2, and with diethylamine, (CH3CH2)2NH.

Answer

19-11 §19.8 source ↗

Imine formation is reversible. Show all the steps involved in the acid-catalyzed reaction of an imine with water (hydrolysis) to yield an aldehyde or ketone plus primary amine.

Answer

The steps are the exact reverse of the forward reaction shown in Figure 19.7.
Figure 19.7 in the book ↗

19-12 §19.8 source ↗

Draw the following molecule as a skeletal structure, and show how it can be prepared from a ketone and an amine.

Answer

19-13 §19.9 source ↗

Show how you could prepare the following compounds from 4-methyl-3-penten-2-one, (CH3)2C = CHCOCH3.
(a)
(b)
(c)

Answer (3 parts)

(a)
H2/Pd
(b)
N2H4, KOH
(c)
1. H2/Pd; 2. N2H4, KOH

19-14 §19.10 source ↗

Show all the steps in the acid-catalyzed formation of a cyclic acetal from ethylene glycol and an aldehyde or ketone.

Answer

The mechanism is identical to that between a ketone and 2 equivalents of a monoalcohol, shown in Figure 19.11.
Figure 19.11 in the book ↗

19-15 §19.10 source ↗

Identify the carbonyl compound and the alcohol that were used to prepare the following acetal:

Answer

19-16 §19.11 source ↗

What carbonyl compound and what phosphorus ylide might you use to prepare each of the following compounds?
(a)
(b)
(c)
(d)
(e)
(f)

Answer (6 parts)

(a)
Cyclohexanone + (Ph)3P = CHCH3
(b)
Cyclohexanecarbaldehyde + (Ph)3P = CH2
(c)
Acetone + (Ph)3P = CHCH2CH2CH3
(d)
Acetone + (Ph)3P = CHPh
(e)
PhCOCH3 + (Ph)3P = CHPh
(f)
2-Cyclohexenone + (Ph)3P = CH2

19-17 §19.11 source ↗

β-Carotene, a yellow food-coloring agent and dietary source of vitamin A can be prepared by a double Wittig reaction between 2 equivalents of β-ionylideneacetaldehyde and a diylide. Show the structure of the β-carotene product.

Answer

19-18 §19.12 source ↗

When o-phthalaldehyde is treated with base, o-(hydroxymethyl)benzoic acid is formed. Show the mechanism of this reaction.

Answer

Intramolecular Cannizzaro reaction

19-19 §19.12 source ↗

What is the stereochemistry of the pyruvate reduction shown in Figure 19.13? Does NADH lose its pro-R or pro-S hydrogen? Does addition occur to the Si face or Re face of pyruvate? (Review Section 5.11.)
Figure 19.13 in the book ↗
Mechanism of biological aldehyde and ketone reductions by the coenzyme NADH. The key step is an expulsion of hydride ion from NADH and donation to the carbonyl group.

Answer

Addition of the pro-R hydrogen of NADH takes place on the Re face of pyruvate.

19-20 §19.13 source ↗

Assign R or S stereochemistry to the two chirality centers in isocitrate, and tell whether OH and H add to the Si face or the Re face of the double bond.

Answer

The −OH group adds to the Re face at C2, and −H adds to the Re face at C3, to yield (2R,3S)-isocitrate.

19-21 §19.13 source ↗

Treatment of 2-cyclohexenone with HCN/KCN yields a saturated keto nitrile rather than an unsaturated cyanohydrin. Show the structure of the product, and propose a mechanism for the reaction.

Answer

19-22 §19.13 source ↗

How might conjugate addition reactions of lithium diorganocopper reagents be used to synthesize the following compounds?
(a)
(b)
(c)
(d)

Answer (4 parts)

(a)
3-Buten-2-one + (CH3CH2CH2)2CuLi
(b)
3-Methyl-2-cyclohexenone + (CH3)2CuLi
(c)
4-tert-Butyl-2-cyclohexenone + (CH3CH2)2CuLi
(d)
Unsaturated ketone + (H2C = CH)2CuLi

19-23 §19.14 source ↗

How might you use IR spectroscopy to determine whether reaction between 2-cyclohexenone and lithium dimethylcopper gives the direct addition product or the conjugate addition product?

Answer

Look for appearance of either an alcohol or a saturated ketone in the product.

19-24 §19.14 source ↗

Where would you expect each of the following compounds to absorb in the IR spectrum?
(a)
4-Penten-2-one
(b)
3-Penten-2-one
(c)
2,2-Dimethylcyclopentanone
(d)
m-Chlorobenzaldehyde
(e)
3-Cyclohexenone
(f)
2-Hexenal

Answer (6 parts)

(a)
1715 cm−1
(b)
1685 cm−1
(c)
1750 cm−1
(d)
1705 cm−1
(e)
1715 cm−1
(f)
1705 cm−1

19-25 §19.14 source ↗

How might you use mass spectrometry to distinguish between the following pairs of isomers?
(a)
3-Methyl-2-hexanone and 4-methyl-2-hexanone
(b)
3-Heptanone and 4-heptanone
(c)
2-Methylpentanal and 3-methylpentanal

Answer (3 parts)

(a)
Different peaks due to McLafferty rearrangement
(b)
Different peaks due to α cleavage and McLafferty rearrangement
(c)
Different peaks due to McLafferty rearrangement

19-26 §19.14 source ↗

Describe the prominent IR absorptions and mass spectral peaks you would expect for the following compound:

Answer

IR: 1750 cm−1; MS: 140, 84

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Problems and answers are adapted from Organic Chemistry: A Tenth Edition by John McMurry, OpenStax, and are used under the CC BY-NC-SA 4.0 licence. Access for free at https://openstax.org/books/organic-chemistry/pages/1-why-this-chapter. Illustrations: Copyright Rice University, OpenStax, under CC BY-NC-SA 4.0 license. This adaptation is released under the same licence, is non-commercial, and is neither affiliated with nor endorsed by OpenStax or Rice University.