OrganicChemistry-WEB_lNotFqg-163

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(a) Propose a mechanism for formation of the unsymmetrical anhydride.
(b) Why is the unsymmetrical anhydride unusually reactive?
(c) Why does the unsymmetrical anhydride react as indicated rather than giving a
trifluoroacetate ester plus carboxylic acid?
PROBLEM
21-71
Butacetin is an analgesic (pain-killing) agent that is synthesized commercially from
p-fluoronitrobenzene. Propose a synthesis.
PROBLEM
21-72
Phenyl 4-aminosalicylate is a drug used in the treatment of tuberculosis. Propose a synthesis of this
compound starting from 4-nitrosalicylic acid.
PROBLEM
21-73
N,N-Diethyl-m-toluamide (DEET) is the active ingredient in many insect-repellent preparations.
How might you synthesize this substance from m-bromotoluene?
PROBLEM
21-74
Tranexamic acid, a drug useful against blood clotting, is prepared commercially from
p-methylbenzonitrile. Formulate the steps likely to be used in the synthesis. (Don’t worry about
cis–trans isomers; heating to 300 °C interconverts the isomers.)
PROBLEM
21-75
One frequently used method for preparing methyl esters is by reaction of carboxylic acids with
diazomethane, CH2N2.
The reaction occurs in two steps: (1) protonation of diazomethane by the carboxylic acid to yield
methyldiazonium ion, CH3N2
+, plus a carboxylate ion; and (2) reaction of the carboxylate ion with
CH3N2
+.
(a) Draw two resonance structures of diazomethane, and account for step 1.
21 • Additional Problems 793
(b) What kind of reaction occurs in step 2?
PROBLEM
21-76
Draw the structure of the polymer you would expect to obtain from reaction of dimethyl
terephthalate with a triol such as glycerol. What structural feature would this new polymer have
that was not present in Dacron (Table 21.2)? How do you think this new feature might affect the
properties of the polymer?
PROBLEM
21-77
Assign structures to compounds with the following 1H NMR spectra:
(a) C5H10O2
IR: 1735 cm–1
(b) C11H12O2
IR: 1710 cm–1
PROBLEM
21-78
Propose structures for compounds with the following 1H NMR spectra:
(a) C5H9ClO2
IR: 1735 cm–1
794 21 • Additional Problems
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(b) C7H12O4
IR: 1735 cm–1
PROBLEM
21-79
Propose a structure for the compound with the formula C19H9NO2 and the following IR and NMR
spectra
21 • Additional Problems 795
PROBLEM
21-80
Draw the structure of the compound that produced the following spectra. The infrared spectrum has
strong bands at 1720 and 1738 cm–1.
PROBLEM
21-81
When an amide is formed from an acid chloride or an anhydride, two equivalents of base are
required. However, when an ester is used as the starting material, only one equivalent of base is
needed. Explain this reactivity in terms of basicity of the leaving groups.
PROBLEM
21-82
Epoxy adhesives are prepared in two steps. SN2 reaction of the disodium salt of bisphenol A with
epichlorohydrin forms a “prepolymer,” which is then “cured” by treatment with a triamine such as
H2NCH2CH2NHCH2CH2NH2.
Draw structures to show how addition of the triamine results in a strengthening of the polymer.
796 21 • Additional Problems
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WHY THIS CHAPTER?
CHAPTER 22
Carbonyl Alpha-Substitution Reactions
22.1 Keto–Enol Tautomerism
22.2 Reactivity of Enols: α-Substitution Reactions
22.3 Alpha Halogenation of Aldehydes and Ketones
22.4 Alpha Bromination of Carboxylic Acids
22.5 Acidity of Alpha Hydrogen Atoms: Enolate Ion Formation
22.6 Reactivity of Enolate Ions
22.7 Alkylation of Enolate Ions
As with nucleophilic additions and nucleophilic acyl substitutions, many laboratory
schemes, pharmaceutical syntheses, and biochemical pathways make frequent use of carbonyl α-substitution
reactions. Their great value comes from the fact that they constitute one of the few general methods for forming
carbon–carbon bonds, thereby making it possible to build larger molecules from smaller precursors. In this
chapter, we’ll see how and why these reactions occur.
We said in the Preview of Carbonyl Chemistry that much of the chemistry of carbonyl compounds can be
explained by just four fundamental reaction types: nucleophilic additions, nucleophilic acyl substitutions, α
substitutions, and carbonyl condensations. Having studied the first two of these reactions in the past three
chapters, let’s now look in more detail at the third major carbonyl-group process—the α-substitution reaction.
Alpha-substitution reactions occur at the position next to the carbonyl group—the α position—and involve the
substitution of an α hydrogen atom by an electrophile, E, through either an enol or enolate ion intermediate.
Let’s begin by learning more about these two species.
FIGURE 22.1 Tear gas is a controversial riot-control device used by some military and police forces. It is a simple chloroketone made
by a carbonyl α-substitution reaction. (credit: modification of work “Tear Gas in CWB Hennessy Road View” by The Stand News/Wikimedia
Commons, Public Domain)
CHAPTER CONTENTS
	Chapter 22 Carbonyl Alpha-Substitution Reactions
	Why This Chapter?