Additional Problems 12

Visualizing Chemistry

Problem 12.14
Name the following amines, and identify each as primary, secondary, or tertiary:

(a)

A ball-and-stick model of nitrogen bonded to hydrogen, methyl, and isopropyl groups.

(b)

A ball-and-stick model of cyclopentane with methyl and N H 2 substituents on adjacent carbons.

(c)

A ball-and-stick model of nitrogen bonded to a benzene ring, hydrogen, and an isopropyl group

Problem 12.15
The following compound contains three nitrogen atoms. Rank them in order of increasing basicity.

A ball-and-stick model of a large molecule with different functional groups. Black, grey, red, and blue spheres represent carbon, hydrogen, oxygen, and nitrogen.

Problem 12.16
Name the following amine, including R,S stereochemistry.

A ball-and-stick model of a three-carbon chain with benzene rings on C 1 and C 2, and an N H 2 group on C 1.

Problem 12.17
Which nitrogen atom in the following compound is most basic? Explain.

A ball-and-stick model of a large molecule with different functional groups. Black, grey, and blue spheres represent carbon, hydrogen, and nitrogen.

Mechanism Problems

Problem 12.18
Predict the product(s) for each of the following reactions:

(a)

2-Methyl-1-phenylpropan-1-one reacts with dimethylamine in the presence of sodium borohydride and ethanol to form an unknown product represented by a question mark.

(b)

(1 R,4 S)-Bicyclo[2.2.1]heptan-2-one reacts with pyrrolidine in the presence of sodium borohydride and ethanol to form an unknown product represented by a question mark.

Naming Amines

Problem 12.19
Name the following compounds:

(a)

A benzene ring with an amino substituent. There are two bromine substituents, one ortho and one para to the amino group.

(b)

A cyclopentane ring connected to C H 2 C H 2 N H 2.

(c)

A nitrogen atom with cyclopentyl and ethyl substituents.

(d)

A nitrogen atom with one cyclopentyl and two methyl substituents.

(e)

A five-membered ring incorporating one nitrogen. The nitrogen also has an n-propyl substituent.

(f) The structure of a four-carbon chain in which one terminal carbon is part of a nitrile. The other terminal carbon has an amino substituent.

Problem 12.20
Draw structures corresponding to the following IUPAC names:

(a) N,N-Dimethylaniline

(b) (Cyclohexylmethyl)amine

(c) N-Methylcyclohexylamine

(d) (2-Methylcyclohexyl)amine

(e) 3-(N,N-Dimethylamino)propanoic acid

Problem 12.21
Classify each of the amine and amide nitrogen atoms in the following substances as primary, secondary, or tertiary:

(a)

A five-membered ring incorporating one nitrogen. The nitrogen also has a hydrogen.

(b)

An indole with the substituent C H 2 C H 2 N H C H 3 on C 3.

(c)

The structure of lysergic acid diethylamide, a polycyclic compound with several nitrogens.

Amine Basicity

Problem 12.22
Although pyrrole is a much weaker base than most other amines, it is a much stronger acid (pKa ≈ 15 for the pyrrole versus 35 for diethylamine). The N–H hydrogen is readily abstracted by base to yield the pyrrole anion, C4H4N–. Explain.

Problem 12.23
Histamine, whose release in the body triggers nasal secretions and constricted airways, has three nitrogen atoms. List them in order of increasing basicity and explain your ordering.

The structure of histamine, a five-membered ring incorporating two nitrogens with a carbon between them. There are two double bonds (one nitrogen has a hydrogen), and an ethylamine substituent.

Problem 12.24
Account for the fact that p-nitroaniline (pKa = 1.0) is less basic than m-nitroaniline (pKa = 2.5) by a factor of 30. Draw resonance structures to support your argument. (The pKa values refer to the corresponding ammonium ions.)

Synthesis of Amines

Problem 12.25
How would you prepare the following substances from 1-butanol?

(a) Butylamine

(b) Dibutylamine

(c) Pentylamine

(d) N,N-Dimethylbutylamine

Problem 12.26
How would you prepare the following substances from pentanoic acid?

(a) Pentanamide

(b) Pentylamine

(c) Hexanenitrile

(d) Hexylamine

Problem 12.27
How would you prepare aniline from the following starting materials?

(a) Benzene

(b) Benzamide

(c) Toluene

Problem 12.28
How might you prepare pentylamine from the following starting materials?

(a) Pentanamide

(b) Pentanenitrile

(c) 1-Butene

(d) Hexanamide

(e) 1-Butanol

(f) 5-Decene

(g) Pentanoic acid

Problem 12.29
How might a reductive amination be used to synthesize ephedrine, an amino alcohol that was widely used for the treatment of bronchial asthma?

The structure of ephedrine. It has benzene ring connected to a C H with hydroxyl linked to another C H with methyl. This is connected to N-H linked to methyl.

General Problems

Problem 12.30
Oxazole is a five-membered aromatic heterocycle. Would you expect oxazole to be more basic or less basic than pyrrole? Explain.

The structure of oxazole, a five membered ring with oxygen and nitrogen atoms separated by one carbon. There are double bonds between the adjacent carbons, and between carbon and nitrogen.

Problem 12.31
Protonation of an amide using strong acid occurs on oxygen rather than on nitrogen. Suggest a reason for this behavior, taking resonance into account.

An amide undergoes a reversible reaction with sulfuric acid to produce a protonated product in which oxygen carries a positive charge.

Problem 12.32
Fill in the missing reagents a–d in the following synthesis of racemic methamphetamine from benzene.

Benzene reacts with a to produce allylbenzene. This reacts with b and c to produce 1-phenylpropan-2-one. This reacts with d to form (R, S)-methamphetamine.

Problem 12.33
Cyclopentamine is an amphetamine-like central nervous system stimulant. Propose a synthesis of cyclopentamine from materials of five carbons or less.

The stucture of cyclopentamine. A nitrogen with H, methyl, and isopropyl substituents. There is also a cyclopentane on C 1 of the isopropyl group.

Problem 12.34
Propose a structure for the product with formula C9H17N that results when 2-(2-cyanoethyl)cyclohexanone is reduced catalytically.

2-(2-Cyanoethyl)cyclohexanone reacts with hydrogen and platinum catalyst to form a product whose chemical formula is C 9 H 1 7 N.

Problem 12.35
4-Dimethylaminopyridine (DMAP) acts as a catalyst in acyl transfer reactions. DMAP’s catalytic activity stems from its nucleophilic character at the pyridine nitrogen, not the dimethylamino group. Explain this behavior, taking resonance into account.

The structure of 4-dimethylaminopyridine. It has a pyridine ring linked to a nitrogen connected to two methyl groups.

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