Draw the structures of the following carboxylic acids.

(a) α-methylbutyric acid

(b) 2-bromobutanoic acid

(c) 4-aminopentanoic acid

(d) cis-4-phenylbut-2-enoic acid

Draw the structures of the following carboxylic acids.

(e) trans-2-methylcyclohexanecarboxylic acid

(f) 2,3-dimethylfumaric acid

(g) m-chlorobenzoic acid

(h) 3-methylphthalic acid

Name the following carboxylic acids (when possible, give both a common name and a systematic name).

(a)

(b)

(c)

Name the following carboxylic acids (when possible, give both a common name and a systematic name).

(d)

(e)

(f)

Rank the compounds in each set in order of increasing acid strength.

(a) CH₃CH₂COOH, CH₃CHBrCOOH, CH₃CBr₂COOH

Rank the compounds in each set in order of increasing acid strength.

(b) CH₃CH₂CH₂CHBrCOOH, CH₃CH₂CHBrCH₂COOH, CH₃CHBrCH₂CH₂COOH

Rank the compounds in each set in order of increasing acid strength.

(c)

Suppose you have just synthesized heptanoic acid from heptan-1-ol. The product is contaminated by sodium dichromate, sulfuric acid, heptan-1-ol, and possibly heptanal. Explain how you would use acid–base extractions to purify the heptanoic acid. Use a chart, like that in Figure 20-3, to show where the impurities are at each stage.

Phenols are less acidic than carboxylic acids, with values of pK_a around 10. Phenols are deprotonated by (and therefore soluble in) solutions of sodium hydroxide but not by solutions of sodium bicarbonate. Explain how you would use extractions to isolate the three pure compounds from a mixture of p-cresol (p-methylphenol), cyclohexanone, and benzoic acid.

Oxidation of a primary alcohol to an aldehyde usually gives some over-oxidation to the carboxylic acid. Assume you have used PCC to oxidize pentan-1-ol to pentanal.

(a) Show how you would use acid–base extraction to purify the pentanal.

(b) Which of the expected impurities cannot be removed from pentanal by acid–base extractions? How would you remove this impurity?

The IR spectrum of trans-oct-2-enoic acid is shown. Point out the spectral characteristics that allow you to tell that this is a carboxylic acid, and show which features lead you to conclude that the acid is unsaturated and conjugated.

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How many stereoisomers are possible for c. a ketotriose?

Write the mechanism for the base-catalyzed conversion of D-fructose to D-glucose and D-mannose.

Show how you would synthesize the following carboxylic acids, using the indicated starting materials.

(a) oct-4-yne → butanoic acid

(b) trans-cyclodecene → decanedioic acid

Show how you would synthesize the following carboxylic acids, using the indicated starting materials.

(d) butan-2-ol → 2-methylbutanoic acid

Show how you would synthesize the following carboxylic acids, using the indicated starting materials.

(e) p-xylene → terephthalic acid

Show how you would synthesize the following carboxylic acids, using the indicated starting materials.

(f) allyl iodide → but-3-enoic acid

Propose a mechanism for the acid-catalyzed reaction of acetic acid with ethanol to give ethyl acetate.

The Principle of Microscopic Reversibility states that a forward reaction and a reverse reaction taking place under the same conditions (as in an equilibrium) must follow the same reaction pathway in microscopic detail. The reverse of the Fischer esterification is the acid-catalyzed hydrolysis of an ester. Propose a mechanism for the acid-catalyzed hydrolysis of ethyl benzoate, PhCOOCH₂CH₃.

A carboxylic acid has two oxygen atoms, each with two nonbonding pairs of electrons.

(a) Draw the resonance forms of a carboxylic acid that is protonated on the hydroxy oxygen atom.

(b) Compare the resonance forms with those given previously for an acid protonated on the carbonyl oxygen atom.

(c) Explain why the carbonyl oxygen atom of a carboxylic acid is more basic than the hydroxy oxygen.

Show how Fischer esterification might be used to form the following esters. In each case, suggest a method for driving the reaction to completion.

(a) methyl salicylate

What monosaccharides are formed in a modified Kiliani–Fischer synthesis starting with each of the following monosaccharides?

b. L-threose

Show how Fischer esterification might be used to form the following esters. In each case, suggest a method for driving the reaction to completion.

(c) ethyl phenylacetate

The mechanism of the Fischer esterification was controversial until 1938, when Irving Roberts and Harold Urey of Columbia University used isotopic labeling to follow the alcohol oxygen atom through the reaction. A catalytic amount of sulfuric acid was added to a mixture of 1 mole of acetic acid and 1 mole of special methanol containing the heavy ¹⁸O isotope of oxygen. After a short period, the acid was neutralized to stop the reaction, and the components of the mixture were separated.

(a) Propose a mechanism for this reaction.

(b) Follow the labeled ¹⁸O atom through your mechanism, and show where it is found in the products.

The given was missing some important resonance forms of the intermediates shown in brackets. Complete this mechanism by drawing all the resonance forms of these intermediates. Do your resonance forms help to explain why this reaction occurs under very mild conditions (water with a tiny trace of acid)?

(b) Finish the solution for Solved Problem 20-1 by providing a mechanism for the acid-catalyzed hydrolysis of ethyl formate.

Show how to synthesize the following compounds, using appropriate carboxylic acids and amines.

(a)

Show how to synthesize the following compounds, using appropriate carboxylic acids and amines.

(b)

Show how to synthesize the following compounds, using appropriate carboxylic acids and amines.

(c)

Show how you would synthesize the following compounds from the appropriate carboxylic acids or acid derivatives.