Homework CHAPTER 20 with answers MANDATORY PROBLEMS

Homework Ch. 20—Carboxylic Acids and Nitriles-Yellow marked mandatory
SHORT ANSWER
Drawing Instructions: Draw structures corresponding to each of the given names.
1.
Draw: 2-propylpentanoic acid
ANS:
2.
Draw: cis-1,3-cyclopentanedicarboxylic acid
ANS:
3.
Draw: cyanoacetic acid
ANS:
4.
Draw: m-chlorobenzoic acid
ANS:
1
Carboxylic Acids and Nitriles
5.
Draw: 2-propenenitrile
ANS:
IUPAC Naming Instructions: Provide proper IUPAC names.
6.
Name:
ANS:
1,5-pentanedioic acid
7.
Name:
ANS:
o-hydroxybenzoic acid
8.
Name:
ANS:
5,5-dimethyl-1,3,6-cycloheptatriene-1-carboxylic acid
2
Chapter 20
9.
Name:
ANS:
(R)-3,5-dihydroxy-3-methylpentanoic acid
10.
Name:
ANS:
(E)-2-methyl-2-butenoic acid
11.
Name:
ANS:
phenylacetonitrile or 2-phenylethanenitrile
12.
a.
b.
c.
d.
What is the correct name for the following structure?
2-oxohexanoic acid
5-oxohexanoic acid
methyl butroxoketone
4-ketopentanoic acid
ANS:
b
3
Carboxylic Acids and Nitriles
Exhibit 20-1
Consider the data in the Table below to answer the following question(s):
Y
H
CN
OCH3
13.
Acidities of Substituted Benzoic and Acetic Acids
pKas at 25°C
Y−C6H4COOH
meta
para
Y−CH2COOH
4.75
4.19
4.19
2.47
3.64
3.55
3.57
4.09
4.46
Refer to Exhibit 20-1. Draw the structure of the strongest acid in the table above.
ANS:
NC−CH2−COOH
14.
Refer to Exhibit 20-1. Which of the acids in the table above has the strongest conjugate
base?
ANS:
CH3COOH
15.
Refer to Exhibit 20-1. Explain why cyanoacetic acid and methoxyacetic acid are more acidic
than their correspondingly substituted benzoic acid counterparts.
ANS:
Electron-withdrawing groups, like −CN and −OCH3, inductively withdraw electron density, which
stabilizes the resulting carboxylate anion and, thus, increases the acidity of the carboxylic acid.
These inductive effects are strongly dependent on distance. The −CN and −OCH3 substituents are
closer to the carboxylate in the substituted acetic acids than in the substituted benzoic acids, so
their effect is greater.
16.
Even through the para position is one carbon farther from the carboxy group than the meta
position, p-cyanobenzoic acid is more acidic than m-cyanobenzoic acid. Explain the
differences in acidity between p-cyanobenzoic acid and m-cyanobenzoic acid.
ANS:
In p-cyanobenzoic acid, the negative charge of the carboxylate can be better stabilized than in the
meta isomer because the electron-withdrawing cyano group polarizes the benzene ring and places
a positive charge next to the negatively charged carboxyl group. The same polarization occurs in
m-cyanobenzoic acid, but the effect is not as great because the charge is one carbon farther away
from the carboxy group.
4
Chapter 20
17.
Explain the differences in acidity between p-methoxybenzoic acid and m-methoxybenzoic
acid.
ANS:
p-Methoxybenzoic acid is less acidic than m-methoxybenzoic acid because the carboxyl group is
directly conjugated, through the benzene ring, with the electron-donating oxygen lone pairs of the
methoxy group. This destabilizes the p-methoxybenzoate anion relative to the m-methoxybenzoate
anion by placing two negative charges on the carboxylate group.
Exhibit 20-2
Consider the data below to answer the following question(s).
When CO2 is bubbled through an ether solution of benzylmagnesium bromide, and the resulting
mixture is acidified, phenylacetic acid is produced. Any unreacted benzylmagnesium bromide is
converted to toluene in the acidification step.
5
Carboxylic Acids and Nitriles
18.
Refer to Exhibit 20-2. Write the complete reaction sequence for the process described above.
ANS:
19.
Refer to Exhibit 20-2. How could you separate phenylacetic acid from toluene?
ANS:
Extract the ether solution containing the mixture of products with a dilute aqueous solution of
sodium hydroxide. This converts phenylacetic acid to its carboxylate salt, which will dissolve in
the aqueous layer. The toluene will remain in the ether layer. Separate the aqueous and organic
layers, acidify the aqueous layer, and extract with an organic solvent to recover the phenylacetic
acid.
20.
a.
b.
c.
d.
Refer to Exhibit 20-2. This reaction is described as a _____ process.
carbonylation
carboxylation
carbaniolation
cationation
ANS:
b
Exhibit 20-3
What is the order of increasing acidity for the following compounds? (least to most)
21.
a.
b.
c.
d.
IV, I, III, II
III, II, I, IV
II, III, I, IV
III, II, IV, I
ANS:
B
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Chapter 20
22.
a.
b.
c.
d.
IV, I, III, II
IV, II, III, I
II, III, I, IV
I, III, II, IV
ANS:
a
23.
a.
b.
c.
d.
IV, II, I, III
I, II, IV, III
III, I, II, IV
III, IV, II, I
ANS:
c
Exhibit 20-4
Give the major organic product(s) for each of the following reactions or sequences of reactions.
Show all relevant stereochemistry.
7
Carboxylic Acids and Nitriles
24.
ANS:
25.
ANS:
26.
ANS:
8
Chapter 20
27.
ANS:
28.
ANS:
29.
ANS:
30.
ANS:
9
Carboxylic Acids and Nitriles
31.
ANS:
32.
ANS:
33.
ANS:
Exhibit 20-5
Choose the best reagent(s) for carrying out the following conversions from the list below. Place
the letter corresponding to the best choice in the blank to the left of the conversion.
a.
b.
c.
d.
e.
f.
10
KMnO4, H3O+
CH 3I
NaBH4, ethanol
1. BH3
2. H3O+
1. CH3MgBr, ether
2. H3O+
CrO3, H2SO4, H2O
g.
h.
i.
1. Mg, ether
2. CO2
3. H3O+
1. NaCN
2. H2SO4, H2, heat
O3, then Zn and HOAc
Chapter 20
34.
_____ CH3CH=CHCH2COOH → CH3COOH + HOOCCH2COOH
ANS:
a
35.
_____
ANS:
g
36.
_____
ANS:
f
37.
_____
ANS:
e
Exhibit 20-6
Carboxylic acids are synthesized from alkyl halides via Grignard reagent carboxylation or nitrile
hydrolysis. Choose the best method for effecting each of the following conversions. Explain each
of your choices. If neither method is appropriate, explain.
38.
ANS:
Since SN2 displacements do not occur at tertiary alkyl halides the Grignard reagent carboxylation
is the best method for carrying out this conversion.
11
Carboxylic Acids and Nitriles
39.
ANS:
Amine protons interfere with the formation of Grignard reagents, so nitrile hydrolysis is the best
method for carrying out this conversion.
40.
ANS:
Either method would be appropriate for this conversion.
41.
ANS:
Neither method of acid synthesis yields the desired product. Any Grignard reagent formed will
react with the carbonyl function group present in the starting material. Reaction with cyanide
occurs at the carbonyl functional group as well as at the halogen. However, if the aldehyde is first
protected by forming an acetal, either method can be used to synthesize a carboxylic acid.
42.
12
Propose a synthesis of the anti-inflammatory drug Ibuprofen from benzene. Show all
reagents and all intermediate structures. Assume that ortho and para isomers can be
separated.
Chapter 20
ANS:
Exhibit 20-7
Show how you would accomplish the following transformations. More than one step may be
required. Show all reagents and all intermediate structures.
43.
ANS:
44.
13
Carboxylic Acids and Nitriles
ANS:
45.
Name the following substance. Atoms other than carbon and hydrogen are labeled.
ANS:
4-hydroxy-2,2-dimethylbutanoic acid
46.
Name the following substance. Atoms other than carbon and hydrogen are labeled.
ANS:
3-methylbutanenitrile
14
Chapter 20
47.
Draw the structure of the product formed when the following is treated with 1.) NaOH (aq)
and 2.) H3O+. Explain, if necessary how the product would be affected if the treatment with
acid were omitted.
ANS:
The corresponding conjugate base would be produced.
48.
Draw the structure of the reactant needed to form the following upon treatment with SOCl2
at a moderately elevated temperature. Atoms other than carbon and hydrogen are labeled.
ANS:
15
Carboxylic Acids and Nitriles
MULTIPLE CHOICE
1.
Which of the following is not an acyl derivative of a carboxylic acid?
a. nitrile
c. amide
b. ester
d. acid chloride
ANS: A
2.
a.
b.
c.
d.
e.
Which of the following is not a common feature of both carboxylic acids and nitriles?
carbon atom with three bonds to an electronegative atom
presence of π bonds
can act as electrophiles
occur frequently in living organisms
All characterize both functional group classes.
ANS: D
3.
A solution of glycolic acid is prepared such that the glycolic acid is 69% dissociated.
Calculate the pH of this solution. (
)
a. 3.83
c. 4.18
b. 6.06
d. 3.48
ANS: C
4.
a.
b.
c.
d.
e.
Calculate the percent dissociation of a 0.00100 M solution of lactic acid which has a pH of
4.00. (
)
39%
58%
42%
78%
Nearly 100%
ANS: B
5.
In a solution of acetic acid (
to represent this substance as:
a. CH3CO2H
b. CH3CO2–
c. CH3CO2H and CH3CO2–
ANS: B
16
) at physiological pH of 7.3, it is most accurate
Chapter 20
6.
a.
b.
c.
d.
e.
f.
What reactant could produce the following substance upon treatment with CrO3 under acidic
conditions? Atoms other than carbon and hydrogen are labeled.
2, 2-dimethylbutanal
2, 2-dimethyl-1-butanol
2, 2-dimethylbutanenitrile
a and b
a and c
a, b, and c
ANS: D
7.
a.
b.
c.
d.
e.
In order to produce a carboxylic acid as a product of the Grignard reaction, the Grignard
reagent reacts with:
CO2
a methyl ketone
a methyl ester
an aldehyde
either or CO2 a methyl ketone
ANS: A
8.
a.
b.
c.
d.
e.
Which labeled peaks in the following spectrum are characteristic of a carboxylic acid?
1
2
3
4
5
17
Carboxylic Acids and Nitriles
f. 1 and 2
g. 2 and 3
h. All five peaks
ANS: F
9.
a.
b.
c.
d.
e.
Which labeled peaks would disappear if D2O were added to the sample?
1
2
3
4
All peaks would disappear.
ANS: D
10.
a.
b.
c.
d.
e.
f.
The following spectrum is representative which of the following types of compounds?
carboxylic acid
aldehyde
nitrile
alcohol
halide
Data presented does not provide enough information.
ANS: C
11.
A sample is know to contain either hexanoic acid or 3-methylpentanoic acid. Which of the
following spectra would not distinguish between the two isomers?
a. 1H NMR
b. 13C NMR
c. DEPT-90
18
Chapter 20
d. DEPT-135
e. All would distinguish between the two isomers.
ANS: B
19