Additional Problems 11: Carboxylic Acids and Nitriles

Visualizing Chemistry

Problem 11.34
Give IUPAC names for the following carboxylic acids (reddish brown = Br):

(a)

A ball-and-stick model of a benzene ring with a carboxyl group, a bromine meta to the carboxyl, and a methoxy group para to the carboxyl.

(b)

A ball-and-stick model of a four-carbon chain with a carboxyl end. There is a double bond on C 2 and a methyl on C 3.

(c)

The ball-and-stick model represents a cyclopentadiene ring with a carboxylic acid group attached to C 1. The double bonds are located on the first and third carbon atoms.

(d)

A ball-and-stick model of a three-carbon chain with a carboxyl end. There is a methyl on C 2 and a cyclopentane on C 3.

Problem 11.35
Would you expect the following carboxylic acids to be more acidic or less acidic than benzoic acid? Explain. (Reddish brown = Br.)

(a)

A ball-and-stick model of a benzene ring with a carboxyl group and a bromine para to the carboxyl.

(b)

A ball-and-stick model of a benzene ring with a carboxyl group and a dimethylamine group para to the carboxyl.

Problem 11.36
The following carboxylic acid can’t be prepared from an alkyl halide by either the nitrile hydrolysis route or the Grignard carboxylation route. Explain.

A ball-and-stick model of a four-carbon chain with a carboxyl end. There are two methyl groups on C 2 and a hydroxy group on C 4.

Problem 11.37
Electrostatic potential maps of anisole and thioanisole are shown. Which do you think is the stronger acid, p-methoxybenzoic acid or p-(methylthio)benzoic acid? Explain.

The ball-and-stick model with electrostatic potential maps of anisole (methoxybenzene) and thioanisole ([methylsulfanyl]benzene).

Mechanism Problems

Problem 11.38
Predict the product(s) for each of the following reactions:

(a)

Conversion of 2-methylbutanenitrile to unknown products depicted by a question mark by reaction with sodium hydroxide and water.

(b)

Conversion of 3-methylbenzonitrile to unknown products depicted by a question mark by reaction with sodium hydroxide and water.

Problem 11.39
Predict the product(s) for of each of the following reactions:

(a)

2-methoxybenzonitrile reacts with methylmagnesium bromide in the presence of ether followed by acidic hydrolysis to give unknown products depicted by a question mark.

(b)

Cyclopropanecarbonitrile reacts with phenylmagnesium bromide in the presence of ether followed by acidic hydrolysis to give unknown products depicted by a question mark.

Problem 11.40
Predict the product(s) for the following reactions.

(a)

Conversion of 3,3-dimethylbutane nitrile to unknown products depicted by a question mark by reaction with hydrochloric acid and water.

(b)

Conversion of 4-methylbenzonitrile to unknown products depicted by a question mark by reaction with hydrochloric acid and water.

Naming Carboxylic Acids and Nitriles

Problem 11.41
Give IUPAC names for the following compounds:

(a)

A six-carbon chain with carboxyl groups on carbons 2 and 5.

(b)

A three-carbon chain in which the first carbon is part of a carboxyl group. There are two methyl groups on the adjacent carbon.

(c)

A benzene ring with a carboxyl substituent. Meta to the carboxyl is a cyano substituent.

(d)

A ten-carbon ring with a carboxyl substituent. There is a double bond on the alpha carbon, with trans orientation.

(e)

A three-carbon chain in which the first carbon is part of a nitrile group. There are two methyl groups on the adjacent carbon.

(f)

A six-carbon chain with a substituent on the third carbon. The substituent has the condensed formula C H 2 C O 2 H.

(g)

A five-carbon chain in which the first carbon is part of a carboxyl group. There are bromine groups on the furthest and next-to-furthest carbons from the carboxyl.

(h)

A cyclopentene with a cyano substituent one carbon from the end of the double bond.

Problem 11.42
Draw structures corresponding to the following IUPAC names:

(a) cis-1,2-Cyclohexanedicarboxylic acid

(b) Heptanedioic acid

(c) 2-Hexen-4-ynoic acid

(d) 4-Ethyl-2-propyloctanoic acid

(e) 3-Chlorophthalic acid

(f) Triphenylacetic acid

(g) 2-Cyclobutenecarbonitrile

(h) m-Benzoylbenzonitrile

Problem 11.43
Draw and name the following compounds:

(a) The eight carboxylic acids with the formula C6H12O2

(b) Three nitriles with the formula C5H7N

Problem 11.44
Pregabalin, marketed as Lyrica, is an anticonvulsant drug that is also effective in treating chronic pain. The IUPAC name of pregabalin is (S)-3-(aminomethyl)-5-methylhexanoic acid. (An aminomethyl group is –CH2NH2.) Draw the structure of pregabalin.

Problem 11.45
Isocitric acid, an intermediate in the citric acid cycle of food metabolism, has the systematic name (2R,3S)-3-carboxy-2-hydroxypentanedioic acid. Draw the structure.

Acidity of Carboxylic Acids

Problem 11.46
Order the compounds in each of the following sets with respect to increasing acidity:

(a) Acetic acid, oxalic acid, formic acid

(b) p-Bromobenzoic acid, p-nitrobenzoic acid, 2,4-dinitrobenzoic acid

(c) Fluoroacetic acid, 3-fluoropropanoic acid, iodoacetic acid

Problem 11.47
Arrange the compounds in each of the following sets in order of increasing basicity:

(a) Magnesium acetate, magnesium hydroxide, methylmagnesium bromide

(b) Sodium benzoate, sodium p-nitrobenzoate, sodium acetylide

(c) Lithium hydroxide, lithium ethoxide, lithium formate

Problem 11.48
Calculate the pKa’s of the following acids:

(a) Lactic acid, Ka = 8.4 × 10–4

(b) Acrylic acid, Ka = 5.6 × 10–6

Problem 11.49
Calculate the Ka’s of the following acids:

(a) Citric acid, pKa = 3.14

(b)Tartaric acid, pKa = 2.98

Problem 11.50
Some pKa data for simple dibasic acids is shown. How can you account for the fact that the difference between the first and second ionization constants decreases with increasing distance between the carboxyl groups?

Name

Structure

pKa1

pKa2

Oxalic

HO2CCO2H

1.2

4.2

Succinic

HO2CCH2CH2CO2H

4.2

5.6

Adipic

HO2C(CH2)4CO2H

4.4

5.4

Reactions of Carboxylic Acids and Nitriles

Problem 11.51
How could you convert butanoic acid into the following compounds? Write each step showing the reagents needed.

(a) 1-Butanol

(b) 1-Bromobutane

(c) Pentanoic acid

(d) 1-Butene

Problem 11.52
How could you convert each of the following compounds into butanoic acid? Write each step showing all reagents.

(a) 1-Butanol

(b) 1-Bromobutane

Problem 11.53
How could you convert butanenitrile into the following compounds? Write each step showing the reagents needed.

(a) Butanol

(b) Butylamine

(c) Methyl-3-hexanone

Problem 11.54
How would you prepare the following compounds from benzene? More than one step is needed in each case.

(a) m-Chlorobenzoic acid

(b) p-Bromobenzoic acid

Problem 11.55
Predict the product of the reaction of p-methylbenzoic acid with each of the following:

(a) LiAlH4, then H3O+

(b) CH3MgBr in ether, then H3O+

(c) KMnO4, H3O+

Problem 11.56
1,6-Hexanediamine, a starting material needed for making nylon, can be made from 1,3- butadiene. How would you accomplish the synthesis?

The conversion of buta-1,3-diene to hexane-1,6-diamine. The missing reagents are depicted with a question mark.

General Problems

Problem 11.57
A chemist in need of 2,2-dimethylpentanoic acid decided to synthesize some by reaction of 2-chloro-2-methylpentane with NaCN, followed by hydrolysis of the product. After the reaction sequence was carried out, however, none of the desired product could be found. What do you suppose went wrong?

Problem 11.58
Show how you might prepare the anti-inflammatory agent ibuprofen starting from isobutylbenzene. More than one step is needed.

Chemical structure of isobutylbenzene with arrows pointing toward ibuprofen (isobutyl benzene with substituent in para position: ethyl group with C O 2 H at ethyl C 1).

Problem 11.59
The following pKa values have been measured. Explain why a hydroxyl group in the para position decreases the acidity while a hydroxyl group in the meta position increases the acidity.

The acid strengths of 4-hydroxybenzoic acid (p K a equals 4.48), benzoic acid (p K a equals 4.19), and 3-hydroxybenzoic acid (p K a equals 4.07) are compared.

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