Organic Chemistry

Janice Gorzynski Smith

Chapter 19

Carboxylic Acids and the Acidity of the 0-H Bond - all with Video Answers

Educators

Chapter Questions

Problem 1

Give the IUPAC name for each compound.
a. CH$_3$CH$_2$CH$_2$C(CH$_3$)$_2$CH$_2$COOH
b. CH$_3$CH(Cl)CH$_2$CH$_2$COOH
c. (CH$_3$CH$_2$)$_2$CHCH$_2$CH(CH2CH$_3$)COOH

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Problem 2

Give the structure corresponding to each IUPAC name.
a. 2-bromobutanoic acid
b. 2,3-dimethylpentanoic acid
c. 3,3,4-trimethylheptanoic acid
d. 2-sec-butyl-4,4-diethylnonanoic acid
e. 3,4-diethylcyclohexanecarboxylic acid
f. 1-isopropylcyclobutanecarboxylic acid

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Problem 3

Draw the structure corresponding to each common name:
a. $\alpha$-methoxyvaleric acid
b. $\beta$-phenylpropionic acid
c. $\alpha ,\beta$-dimethylcaproic acid
d. $\alpha$-chloro-$\beta$-methylbutyric acid

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Problem 4

Give the IUPAC name for each metal salt of a carboxylate anion:
(a) $\mathrm{C}_6\mathrm{H}_5\mathrm{CO}_2^- \mathrm{Li}^+$;
(b) $\mathrm{HCO}_2^- \mathrm{Na}^+$;
(c) $(\mathrm{CH}_3)_2\mathrm{CHCO}_2^- \mathrm{K}^+$;
(d) $(\mathrm{CH}_3\mathrm{CH}_2)_2\mathrm{CHCH}_2\mathrm{CH}(\mathrm{Br})\mathrm{CH}_2\mathrm{CH}_2\mathrm{CO}_2^- \mathrm{Na}^+$.

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Problem 5

Depakote, a drug used to treat seizures and bipolar disorder, consists of a mixture of valproic acid
[(CH$_3$CH$_2$CH$_2$)$_2$CHCO$_2$H) and its sodium salt. Give IUPAC names for each of these compounds.

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Problem 6

Rank the following compounds in order of increasing boiling point. Which compound is the most
water soluble? Which compound is the least water soluble?

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Problem 7

Explain how you could use IR spectroscopy to distinguish among the following three compounds.

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Problem 8

Identify the structure of a compound of molecular formula $\mathrm{C}_4\mathrm{H}_8\mathrm{O}_2$ that gives the following $^1$H NMR
data: 0.95 (triplet, 3 H), 1.65 (multiplet, 2 H), 2.30 (triplet, 2 H), and 11.8 (singlet, 1 H) ppm.

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Problem 9

How many tetrahedral stereogenic centers does PGF$_{2\alpha}$ contain? Draw its enantiomer. How many of its double bonds can exhibit cis-trans isomerism? Considering both its double bonds and its tetrahedral stereogenic centers, how many stereoisomers are possible for PGF$_{2\alpha}$?

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Problem 10

What alcohol can be oxidized to each carboxylic acid?

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Problem 11

Identify A-D in the following reactions.

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Problem 12

Draw the products of each acid-base reaction.

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Problem 13

Given the p$K_a$ values in Appendix A, which of the following bases are strong enough to
deprotonate CH$_3$COOH: (a) F$^-$; {b) (CH$_3$}$_3$Co$^-$; (c) CH$_3^-$; {d) $^-$NH2; (e) CI$^-$?

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Problem 14

Rank the labeled protons (H$_a$-H$_c$) in mandelic acid, a naturally occurring carboxylic acid in plums
and peaches, in order of increasing acidity. Explain in detail why you chose this order.

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Problem 15

Match each of the following p$K_a$ values (3.2, 4.9, and 0.2) to the appropriate carboxylic acid:
(a) CH$_3$CH$_2$COOH;
(b) CF$_3$COOH;
(c) ICH$_2$COOH.

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Problem 16

Rank the compounds in each group in order o! increasing acidity.
a. CH$_3$COOH, HSCH$_2$COOH, HOCH$_2$COOH
b. ICH$_2$COOH, I$_2$CHCOOH, ICH$_2$CH$_2$COOH

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Problem 17

Rank the compounds in each group in order of increasing acidity.

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Problem 18

Substituted phenols show substituent effects similiar to substituted benzoic acids. Should the p$K_a$ of phenol $\textbf{A}$, one of the naturally occurring phenols called urushiols isolated from poison ivy, be higher or lower than the p$K_a$ of phenol (C$_6$H$_5$OH, p$K_a$ = 1 0)? Explain.

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Problem 19

Which of the following pairs of compounds can be separated from each other by an extraction
procedure?
a. CH$_3$(CH$_2$)$_6$COOH and CH$_3$CH$_2$CH$_2$CH$_2$CH=CH$_2$
b. CH$_3$CH$_2$CH$_2$CH$_2$CH=CH$_2$ and (CH$_3$CH$_2$CH$_2$)$_2$O
c. CH$_3$(CH$_2$)$_6$COOH and NaCl
d. NaCl and KCI

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Problem 20

Two other commonly used sulfonic acids are methanesulfonic acid (CH$_3$SO$_3$H) and trifluoromethanesulfonic acid (CF$_3$SO$_3$H). Which has the weaker conjugate base? Which conjugate base is the better leaving group? Which of these acids has the higher p$K_a$?

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Problem 21

Draw both enantiomers of each amino acid and label them as $R$ or $S$: (a) phenylalanine;
(b) methionine.

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Problem 22

Explain why amino acids, unlike most other organic compounds, are insoluble in organic solvents
like diethyl ether.

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Problem 23

Draw the positively charged, neutral, and negatively charged forms for the amino acid glycine. Which species predominates at pH 11? Which species predominates at pH 1?

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Problem 24

The p$K_a$ values for the carboxy and ammonium protons of phenylalanine are 2.58 and 9.24,
respectively. What is the isoelectric point of phenylalanine? Draw the structure of phenylalanine at
its isoelectric point.

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Problem 25

Explain why the p$K_a$ of the COOH group of glycine is much lower than the p$K_a$ of the COOH of
acetic acid (2.35 compared to 4.8).

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Problem 26

Answer each question for $\textbf{A}$ and $\textbf{B}$ depicted in the ball-and-stick models.
a. What is the IUPAC name for each compound?
b. What product is formed when each compound is treated with NaOH?
c. Name the products formed in part (b).
d. Draw the structure of an isomer that is at least 10$^5$ times less acidic than each compound.

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Problem 27

Rank the carboxylic acids in order of increasing acidity.

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Problem 28

Give the IUPAC name for each compound.

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Problem 29

Draw the structure corresponding to each name.
a. 3,3-dimethylpentanoic acid
b. 4-chloro-3-phenylheptanoic acid
c. ($2R$)-2-chloropropanoic acid
d. $\beta.\beta$-dichloropropionic acid
e. $m$-hydroxybenzoic acid
f. $o$-chlorobenzoic acid
g. potassium acetate
h. sodium $\alpha$-bromobutyrate
i. 2,2-dichloropentanedioic acid
j. 4-isopropyl-2-methyloctanedioic acid

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Problem 30

Draw the structures and give the IUPAC names for the carboxylic acids having molecular formula C$_5$H$_{10}$O$_2$ . Then give the IUPAC names for the sodium salts that result from treatment of each carboxylic acid with NaOH.

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Problem 31

Give an IUPAC and common name for each of the following naturally occurring carboxylic acids: (a) CH$_3$CH(OH)CO$_2$H (lactic acid); (b) HOCH$_2$CH$_2$C(OH)(CH$_3$)CH$_2$CO$_2$H (mevalonic acid).

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Problem 32

Rank the compounds in each group in order of increasing boiling point.
a. CH$_3$CH$_2$CH$_2$CH$_2$COOH, (CH$_3$CH$_2$CH$_2$)$_2$0, CH$_3$(CH$_2$)$_5$OH
b. CH$_3$COCH$_2$CH(CH$_3$)$_2$, (CH$_3$HCHCH$_2$COOH, (CH$_3$)$_2$CHCH$_2$CH(OH)CH$_3$

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Problem 33

Draw the organic products formed in each reaction.

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Problem 34

Identify the lettered compounds in each reaction sequence.

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Problem 35

Using the p$K_a$ table in Appendix A, determine whether each of the following bases is strong enough to deprotonate the three compounds listed below. Bases: [1]$^-$OH; [2] CH$_3$CH$_2^-$; [3]$^-$NH$_2$; [4] NH$_3$; [5] HC=C$^-$.

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Problem 36

Draw the products of each acid-base reaction, and using the p$K_a$ table in Appendix A, determine if equilibrium favors the reactants or products.

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Problem 37

Which compound in each pair has the lower p$K_a$? Which compound in each pair has the stronger conjugate base?

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Problem 38

Rank the compounds in each group in order of increasing acidity.

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Problem 39

Rank the compounds in each group in order of increasing basicity.
a. BrCH$_2$COO$^-$ (CH$_3$)$_3$CCOO$^-$ BrCH$_2$CH$_2$COO$^-$
b. C$_6$H$_5$NH$^-$ C$_6$H$_5$O$^-$ C$_6$H$_5$CH$_2^-$

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Problem 40

Match the $pK_a$ values to the appropriate structure. p$K_a$ values: 0.28, 1.24, 2.66, 2.86, and 3.12. Compounds: (a) FCH$_2$COOH; (b) CF$_3$COOH; (c) F$_2$CHCOOH; (d) ICH$_2$COOH; (e) BrCH$_2$COOH.

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Problem 41

Although codeine occurs in low concentration in the opium poppy, most of the codeine used in medicine is prepared from morphine (the principal component of opium) by the following reaction. Explain why selective methylation occurs at only one OH in morphine to give codeine. Codeine is a less potent and less addictive analgesic than morphine.

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Problem 42

Which carboxylic acid has the lower p$K_a$ , pyruvic acid (CH$_3$COCO$_2$H) or acetoacetic acid (CH$_3$COCH2CO$_2$H)? Explain your choice.

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Problem 43

Explain each statement.
a. The p$K_a$ of $p$-nitrophenol is lower than the p$K_a$ of phenol (7.2 vs. 10).
b. The p$K_a$ of $p$-nitrophenol is lower than the p$K_a$ of $m$-nitrophenol (7.2 vs. 8.3).

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Problem 44

Explain the following statement. Although 2-methoxyacetic acid (CH$_3$OCH$_2$COOH) is a stronger acid than acetic acid (CH$_3$COOH), $p$-methoxybenzoic acid (CH$_3$OC$_6$H$_4$COOH) is a weaker acid than benzoic acid (C$_6$H$_5$COOH).

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Problem 45

The $pK_a$ of p-methylthiophenol (CH$_3$SC$_6$H$_4$OH) is 9.53. Is $_p$-methylthiophenol more or less reactive in electrophilic aromatic substitution than phenol?

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Problem 46

Explain why the p$K_a$ of compound $\textbf{A}$ is lower than the p$K_a$'s of both compounds $\textbf{B}$ and $\textbf{C.}$

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Problem 47

Rank the following compounds in order of increasing acidity and explain in detail your choice of order

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Problem 48

Explain the following result. Acetic acid (CH$_3$COOH), labeled at its OH oxygen with the uncommon $^{18}$O isotope, was treated with aqueous base, and then the solution was acidified. Two products having the $^{18}$O label at different locations were formed.

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Problem 49

Draw all resonance structures of the conjugate bases formed by removal of the labeled protons (H$_a$, H$_b$, and H$_c$) in 1,3-cyclohexanedione and acetanilide. For each compound, rank these protons in order of increasing acidity and explain the order you chose.

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Problem 50

As we will see in Chapter 23, C-H bonds are sometimes more acidic than O-H bonds. Explain why the p$K_a$ of CH$_2$(CHO)$_2$ is lower than the p$K_a$ of HO(CH$_2$)$_3$OH (9 vs. 16).

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Problem 51

Identify $\textbf{X}$ in the following equation, and explain how hexanoic acid, the chapter-opening molecule, is formed by this stepwise reaction sequence.

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Problem 52

The p$K_a$ of acetamide (CH$_3$CONH$_2$) is 16. Draw the structure for its conjugate base and explain why acetamide is less acidic than CH$_3$COOH.

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Problem 53

Write out the steps needed to separate hydrocarbon $\textbf{A}$ and carboxylic acid $\textbf{B}$ by using an extraction procedure.

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Problem 54

Because phenol (C$_6$H$_5$OH) is less acidic than a carboxylic acid, it can be deprotonated by NaOH but not by the weaker base NaHCO$_3$. Using this information, write out an extraction sequence that can be used to separate C$_6$H$_5$OH from cyclohexanol. Show what compound is present in each layer at each stage of the process, and if it is present in its neutral or ionic form.

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Problem 55

Can octane and 1-octanol be separated using an aqueous extraction procedure? Explain why or why not.

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Problem 56

Identify each compound from its spectral data.
a. Molecular formula: C$_3$H$_5$CIO$_2$
IR: 3500-2500 cm$^{-1}$, 1714 cm$^{-1}$
$^1$H NMR data: 2.87 (triplet, 2 H), 3.76 (triplet, 2 H), and 11.8 (singlet, 1 H) ppm
b. Molecular formula: C$_8$H$_8$O$_3$
IR: 3500-2500 cm$^{-1}$, 1688 cm$^{-1}$
$^1$H NMR data: 3.8 (singlet, 3 H), 7.0 (doublet, 2 H), 7.9 (doublet, 2 H), and 12.7 (singlet, 1 H) ppm
c. Molecular formula: C$_8$H$_8$O$_3$
$^1$H NMR data: 4.7 (singlet, 2 H), 6.9-7.3 (multiplet, 5 H), and 11.3 (singlet, 1 H) ppm

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Problem 57

Use the $^1$H NMR and IR spectra given below to identify the structures of two isomers ($\textbf{A}$ and $\textbf{B}$) having molecular formula C$_4$H$_8$O$_2$.

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Problem 58

An unknown compound $\textbf{C}$ (molecular formula C$_4$H$_8$O$_3$) exhibits IR absorptions at 3600-2500 and 1734 cm$^{-1}$, as well as the following $^1$H NMR spectrum. What is the structure of $\textbf{C}$?

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Problem 59

Propose a structure for $\textbf{D}$ (molecular formula C$_9$H$_9$CIO$_2$) consistent with the given spectroscopic data. $^{13}$C NMR signals at 30, 36, 128, 130, 133, 139, and 179 ppm

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Problem 60

A monomer needed to synthesize polyethylene terephthalate (PET), a polymer used to make plastic sheeting and soft drink bottles (Section 22.16), shows a strong absorption in its IR spectrum at 1692 cm$^{-1}$ and two singlets in its $^1$H NMR spectrum at 8.2 and 10.0 ppm. What is the structure of this monomer (molecular formula C$_8$H$_6$O$_4$)?

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Problem 61

Match the $^{13}$C NMR data to the appropriate structure.
Spectrum [1]: signals at 14, 22, 27, 34,181 ppm
Spectrum [2]: signals at 27, 39, 186 ppm
Spectrum [3]: signals at 22, 26, 43, 180 ppm

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Problem 62

$\gamma$-Butyrolactone (C$_4$H$_6$O$_2$ , GBL) is a biologically inactive compound that is converted to the biologically active recreational drug GHB (Section 19.5) by a lactonase enzyme in the body. Since $\gamma$-butyrolactone is more fat soluble than GHB, it is more readily absorbed by tissues and thus produces a faster onset of physiological symptoms. $\gamma$-Butyrolactone shows an absorption in its IR spectrum at 1770 cm$^{-1}$ and the following 1H NMR spectral data: 2.28 (multiplet, 2 H), 2.48 (triplet, 2 H), and 4.35 (triplet, 2 H) ppm. What is the structure of y-butyrolactone?

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Problem 63

Threonine is a naturally occurring amino acid that has two stereogenic centers.
a. Draw the four possible stereoisomers using wedges and dashes.
b. The naturally occurring amino acid has the $2S,3R$ configuration at its two stereogenic centers. Which structure does this correspond to?

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Problem 64

Praline is an unusual amino acid because its N atom on the $\alpha$ carbon is part of a five-membered ring.
a. Draw both enantiomers of praline.
b. Draw praline in its zwitterionic form.

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Problem 65

For each amino acid [RCH(NH$_2$)COOH], draw its neutral, positively charged, and negatively charged forms. Which form predominates at pH = 1, 6, and 11? What is the structure of each amino acid at its isoelectric point?
a. methionine (R = CH$_2$CH$_2$SCH$_3$)
b. serine (R = CH$_2$OH)

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Problem 66

Calculate the isoelectric point for each amino acid.
a. cysteine: p$K_a$ (COOH) = 2.05; p$K_a$ ($\alpha$-NH$_3^+$) = 10.25
b. methionine: p$K_a$ (COOH) = 2.28; p$K_a$ ($\alpha$-NH$_3^+$) = 9.21

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Problem 67

Lysine and tryptophan are two amino acids that contain an additional N atom in the R group bonded to the $\alpha$ carbon. While lysine is classified as a basic amino acid because it contains an additional basic N atom, tryptophan is classified as a neutral amino acid. Explain why this difference in classification occurs.

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Problem 68

Amino acids can be prepared from a-halo carboxylic acids [RCH(X)COOH] by reaction with excess NH$_3$. Why is excess NH$_3$
needed for this reaction?

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Problem 69

G/utamic acid is a naturally occurring $\alpha$-amino acid that contains a carboxy group in its R group side chain (Table 19.4). (Glutamic acid is drawn in its neutral form with no charged atoms, a form that does not actually exist at any pH.)
a. What form of glutamic acid exists at pH = 1?
b. If the pH is gradually increased, what form of glutamic acid exists after one equivalent of base is added? After two equivalents? After three equivalents?
c. Propose a structure of monosodium glutamate, the common flavor enhancer known as MSG.

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Problem 70

Explain why using one or two equivalents of NaH results in different products in the following reactions.

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Problem 71

Although $p$-hydroxybenzoic acid is less acidic than benzoic acid, o-hydroxybenzoic acid is slightly more acidic than benzoic acid. Explain this result.

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Problem 72

2-Hydroxybutanedioic acid occurs naturally in apples and other fruits. Rank the labeled protons (H$_a$-H$_e$) in order of increasing acidity and explain in detail the order you chose.

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Problem 73

Although it was initially sold as a rat poison, warfarin is an effective anticoagulant used to prevent blood clots. Label the most acidic proton in warfarin, and explain why its p$K_a$ is comparable to the p$K_a$ of a carboxylic acid.

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