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Organic Chemistry

Janice Gorzynski Smith

Chapter 22

Carboxylic Acids and Their DerivativesNucleophilic Acyl Substitution

Educators


Problem 1

Oxytocin, sold under the trade name Pitocin, is a naturally occurring hormone used to stimulate
uterine contractions and induce labor. Classify each amide in oxytocin as 1$^\circ$, 2$^\circ$, or 3$^\circ$.

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Problem 2

Draw the three possible resonance structures for an acid bromide, RCOBr. Then, using the pKa
values in Appendix A, decide if RCOBr is more or less stabilized by resonance than a carboxylic
acid (RCOOH).

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Problem 3

How do the following experimental results support the resonance description of the relative
stability of acid chlorides compared to amides? The C- Cl bond lengths in CH$_3$CI and CH$_3$COCI
are identical (178 pm), but the C- N bond in HCONH$_2$ is shorter than the C- N bond in CH$_3$NH$_2$
(135 pm versus 147 pm).

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Problem 4

Give an IUPAC or common name for each compound.

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Problem 5

Draw the structure corresponding to each name.
a. 5-methylheptanoyl chloride
b. isopropyl propanoate
c. acetic formic anhydride
d. $N$-isobutyl-$N$-methylbutanamide
e. 3-methylpentanenitrile
f. o-cyanobenzoic acid
g. sec-butyl 2-methylhexanoate
h. $N$-ethylhexanamide

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Problem 6

Explain why the boiling point of CH$_3$CONH$_2$ (221 $^\circ$C) is significantly higher than the boiling point of CH$_3$CON(CH$_3$)$_2$ (166 $^\circ$C), even though the latter compound has a higher molecular weight and more surface area.

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Problem 7

How would the compounds in each pair differ in their IR spectra?

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Problem 8

Deduce the structures of compounds $\textbf{A}$ and $\textbf{B}$, two of the major components of jasmine oil, from the given data.
Compound A: C$_9$H$_{10}$O$_2$; IR absorption's at 3091-2895 and 1743 cm$^{-1}$; $^1$H NMR signals at 2.06 (singlet, 3 H), 5.08 (singlet, 2 H), and 7.33 (broad singlet, 5 H) ppm.
Compound B: C$_{14}$H$_{12}$O$_2$; IR absorptions at 3091-2953 and 1718 cm$^{-1}$; $^1$H NMR signals at 5.35 (singlet, 2 H) and 7.26-8.15 (multiplets, 10 H) ppm.

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Problem 9

Without reading ahead in Chapter 22, state whether it should be possible to carry out each of the
following nucleophilic substitution reactions.

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Problem 10

Rank the compounds in each group in order of increasing reactivity in nucleophilic acyl substitution.
a. C$_6$H$_5$COOCH$_3$ , C$_6$H$_5$COCI, C$_6$H$_5$CONH$_2$
b. CH$_3$CH$_2$COOH, (CH$_3$CH$_2$CO)$_2$O, CH$_3$CH$_2$CONHCH$_3$

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Problem 11

Explain why trichloroacetic anhydride [(Cl$_3$CCO)$_2$0] is more reactive than acetic anhydride
[(CH$_3$C0)$_2$O] in nucleophilic acyl substitution reactions.

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Problem 12

Draw the products formed when benzoyl chloride (C$_6$H$_5$COCI) is treated with each nucleophile:
(a) H$_2$O, pyridine; (b) CH$_3$COO$^-$; (c) NH$_3$ (excess); (d) (CH$_3$)$_2$NH (excess).

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Problem 13

Draw a stepwise mechanism for the formation of $\textbf{A}$ from an alcohol and acid chloride. $\textbf{A}$ was converted in one step to blattellaquinone, the sex pheromone of the female German cockroach $\textit{Blattella germanica}$.

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Problem 14

Draw the products formed when benzoic anhydride [(C$_6$H$_5$CO)$_2$O] is treated with each nucleophile:
(a) H$_2$0; (b) CH$_3$OH; (c) NH$_3$ (excess); (d) (CH$_3$)$_2$NH (excess).

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Problem 15

Draw the products of each reaction.

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Problem 15

Draw the products of each reaction.

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Problem 16

Draw the products of each reaction.

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Problem 17

Draw the products formed when benzoic acid (C$_6$H$_5$COOH) is treated with CH$_3$OH having its O atom labeled with $^{18}$O (CH$_3$$^{18}$OH). Indicate where the labeled oxygen atom resides in the products.

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Problem 18

Draw a stepwise mechanism for the following reaction.

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Problem 19

What product is formed when acetic acid is treated with each reagent: (a) CH$_3$NH$_2$; (b) CH$_3$NH$_2$, then heat; (c) CH$_3$NH$_2$ + DCC?

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Problem 20

Sunscreens that contain esters can slowly degrade over time because the ester can be hydrolyzed.
Draw the products formed when each commercial sunscreen undergoes hydrolysis with [1] H$_3$O$^+$ or [2] H$_2$O, $^-$OH.

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Problem 21

What product is formed when the esters in ginkgolide B, the chapter-opening molecule, are
hydrolyzed in aqueous acid? Indicate the stereochemistry of all stereogenic centers.

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Problem 22

How would you synthesize olestra from sucrose?

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Problem 23

What is the composition of the soap prepared by hydrolysis of this triacylglycerol?

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Problem 24

Draw a stepwise mechanism for the following reaction.

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Problem 25

With reference to the structures of acetylsalicylic acid (aspirin, Chapter 2 opening molecule) and
acetaminophen (the active ingredient in Tylenol), explain each statement: (a) Acetaminophen
tablets can be stored in the medicine cabinet for years, but aspirin slowly decomposes over time;
(b) Children's Tylenol can be sold as a liquid (acetaminophen dissolved in water), but aspirin cannot.

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Problem 26

Some penicillins cannot be administered orally because their $\beta$-lactam is rapidly hydrolyzed by the acidic environment of the stomach. What product is formed in the following hydrolysis reaction?

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Problem 27

What two monomers are needed to prepare nylon 6,10?

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Problem 28

Draw the structure of Kadel, a polyester formed from 1,4-dihydroxymethylcyclohexane and
terephthalic acid. Explain why fabrics made from Kadel are stiff and crease resistant.

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Problem 29

Poly(lactic acid) (PLA) has received much recent attention because the lactic acid monomer
[CH$_3$CH(OH)COOH] from which it is made can be obtained from carbohydrates rather than
petroleum. This makes PLA a more "environmentally friendly" polyester. (A more in-depth
discussion of green polymer synthesis is presented in Section 31.8.) Draw the structure of PLA.

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Problem 30

Glucosamine is a dietary supplement available in many over-the-counter treatments for
osteoarthritis. Reaction of acetyl CoA with glucosamine forms NAG, $N$-acetylglucosamine, the
monomer used to form chitin, the carbohydrate that forms the rigid shells of lobsters and crabs.
What is the structure of NAG?

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Problem 31

Draw the products of each reaction.

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Problem 32

Draw a tautomer of each compound.

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Problem 33

Draw the product of each reaction.

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Problem 34

Draw the products of each reaction.

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Problem 35

What reagents are needed to convert phenylacetonitrile (C$_6$H$_5$CH$_2$CN) to each compound: (a) C$_6$H$_5$CH$_2$COCH$_3$ ; (b) C$_6$H$_5$CH$_2$COC(CH_$$)$_3$; (c) C$_6$H$_5$CH$_2$CHO; (d) C$_6$H$_5$CH$_2$COOH?

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Problem 36

Outline two different ways that 2-butanone can be prepared from a nitrile and a Grignard reagent.

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Problem 37

Rank the following compounds in order of increasing reactivity in nucleophilic acyl substitution.

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Problem 38

Give an acceptable name for each compound. (b) Draw the organic products formed when A or B is treated with each reagent: [1] H$_3$O$^+$ (2] $^-$OH, H$_2$O; [3] CH$_3$CH$_2$CH2MgBr (excess), then H$_2$O; [4] LiAIH$_4$ , then H$_2$O.

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Problem 39

Which ester, $\textbf{C}$ or $\textbf{D}$, is more reactive in nucleophilic acyl substitution? Explain your reasoning.

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Problem 40

Give the IUPAC or common name for each compound.

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Problem 41

Give the structure corresponding to each name.
a. propanoic anhydride
b. a-chlorobutyryl chloride
c. cyclohexyl propanoate
d. cyclohexanecarboxamide
e. isopropyl formate
f. $N$-cyclopentylpentanamide
g. 4-methylheptanenitrile
h. vinyl acetate
i. benzoic propanoic anhydride
j. 3-methylhexanoyl chloride
k. octyl butanoate
I. $N,N$-dibenzylformamide

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Problem 42

Rank the compounds in each group in order of increasing reactivity in nucleophilic acyl substitution.
a. CH$_3$CH$_2$CH$_2$CONH$_2$, CH$_3$CH$_2$CH$_2$COCI, CH$_3$CH$_2$CH$_2$COOCH$_2$CH$_2$CH$_3$
b. (CH$_3$CH$_2$CO)$_2$O, (CF$_3$CO)$_2$O, CH$_3$CH$_2$CO$_2$CH$_2$CH$_2$CH$_3$

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Problem 43

Explain why imidazolides are much more reactive than other amides in nucleophilic acyl substitution.

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Problem 44

Explain why CH$_3$CONH$_2$ is a stronger acid and a weaker base than CH$_3$CH$_2$NH$_2$

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Problem 45

Draw the product formed when pentanoyl chloride (CH$_3$CH$_2$CH$_2$CH$_2$COCI) is treated with each reagent.
a. H$_2$O, pyridine
b. CH$_3$CH$_2$OH, pyridine
c. CH$_3$COO$^-$
d. NH$_3$ (excess)
e. (CH$_3$CH$_2$)$_2$NH (excess)
f. C$_6$H$_5$NH$_2$ (excess)

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Problem 46

Draw the product formed when pentanoic anhydride [(CH$_3$CH$_2$CH$_2$CH$_2$CO)$_2$O] is treated with each reagent. With some reagents, no reaction occurs.
a. SOCl$_2$
b. H$_2$O
c. CH$_3$OH
d. NaCl
e. (CH$_3$CH$_2$)$_2$NH (excess)
f. CH$_3$CH$_2$NH$_2$ (excess)

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Problem 47

Draw the product formed when phenylacetic acid (C$_6$H$_5$CH$_2$COOH) is treated with each reagent. With some reagents, no reaction occurs.
a. NaHCO$_3$
b. NaOH
c. SOCl$_2$
d. NaCl
e. NH$_3$ (1 equiv)
f. NH$_3$, $\Delta$
g. CH$_3$OH,$\mid$ H$_2$SO$_4$
h. CH$_3$OH, $^-$OH
i. [1] NaOH; [2] CH$_3$COCI
j. CH$_3$NH$_2$, DCC
k. [1] SOCl$_2$; [2] CH$_3$CH$_2$CH$_2$NH$_2$ (excess)
I. [1 ] SOCl$_2$; [2] (CH$_3$)$_3$CHOH

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Problem 48

Draw the product formed when ethyl butanoate (CH$_3$CH$_2$CH$_2$COOCH$_2$CH$_3$) is treated with each reagent. With some reagents, no reaction occurs.
a. SOCl$_2$
b. H$_3$O$^+$
c. H$_2$O, $^-$OH
d. NH$_3$
e. CH$_3$CH$_2$NH$_2$

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Problem 49

Draw the product formed when phenylacetamide (C$_6$H$_5$CH$_2$CONH$_2$) is treated with each reagent.
a. H$_3$O$^+$
b. H$_2$O, $^-$OH

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Problem 50

Draw the product formed when phenylacetonitrile (C$_6$H$_5$CH$_2$CN) is treated with each reagent.
a. H$_3$O$^+$
b. H$_2$O, $^-$OH
c. [1] CH$_3$MgBr; [2] H$_2$O
d. [1] CH$_3$CH$_2$Li; [2] H$_2$O
e. [1] DIBAL-H; [2] H$_2$O
f. [1] LiAIH$_4$; [2] H$_2$O

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Problem 51

Draw the organic products formed in each reaction.

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Problem 52

What products are formed when $\textbf{X}$, which contains both a lactone and an acetal, is treated with each reagent: (a) H$_3$O$^+$ (b) NaOH, H$_2$O?

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Problem 53

Identify compounds $\textbf{A}$- $\textbf{M}$ in the following reaction sequence.
~

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Problem 54

Draw the products of each reaction and indicate the stereochemistry at any stereogenic centers.

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Problem 55

What products are formed when all of the amide and ester bonds are hydrolyzed in each of the following compounds? Tamiflu [part (a)] is the trade name of the antiviral agent oseltamivir, thought to be the most effective agent in treating influenza. Governments are stockpiling the drug in the event of an influenza pandemic. $\textbf{Aspartame}$ [part (b)] is the artificial sweetener used in Equal and many diet beverages. One of the products of this hydrolysis reaction is the amino acid phenylalanine. Infants afflicted with phenylketonuria cannot metabolize this amino acid, so it accumulates, causing mental retardation. When the affliction is identified early, a diet limiting the consumption of phenylalanine (and compounds like aspartame that are converted to it) can make a normal life possible.

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Problem 56

Identify $\textbf{F}$ in the following reaction sequence. $\textbf{F}$ was converted in several steps to the antidepressant paroxetine (trade name Paxil; see also Problem 9.11).

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Problem 57

Draw a stepwise mechanism for each reaction.

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Problem 58

When acetic acid (CH$_3$COOH) is treated with a trace of acid in water labeled with $^{18}$O , the label gradually appears in both oxygen atoms of the carboxylic acid. Draw a mechanism that explains this phenomenon.

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Problem 59

Although $\gamma$-butyrolactone (Problem 19.62) is a biologically inactive compound, it is converted in the body to 4-hydroxybutanoic acid (GHB), an addictive and intoxicating recreational drug (Section 19.5). Draw a stepwise mechanism for this conversion in the presence of acid.

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Problem 60

Aspirin is an anti-inflammatory agent because it inhibits the conversion of arachidonic acid to prostaglandins by the transfer of its acetyl group (CH$_3$CO$^-$) to an OH group at the active site of an enzyme (Section 19.6). This reaction, called transesterification, results in the conversion of one ester to another by a nucleophilic acyl substitution reaction. Draw a stepwise mechanism for the given transesterification.

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Problem 61

Draw a stepwise mechanism for the following reaction, one step in the synthesis of the cholesterol-lowering drug ezetimibe (Section 20.6).

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Problem 61

Draw a stepwise mechanism for the following reaction, one step in the synthesis of the cholesterol-lowering drug ezetimibe (Section 20.6).

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Problem 62

Draw a stepwise mechanism for the conversion of lactone $\textbf{C}$ to carboxylic acid $\textbf{D}$. $\textbf{C}$ is a key intermediate in the synthesis of prostaglandins (Section 19.6) by Nobel Laureate E. J . Corey and co-workers at Harvard University.

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Problem 63

Draw a stepwise mechanism for the conversion of lactone $\textbf{A}$ to ester $\textbf{B}$ using HCI in ethanol. $\textbf{B}$ is converted in one step to ethyl chrysanthemate, a useful intermediate in the synthesis of a variety of pyrethrins, naturally occurring insecticides with threemembered rings that are isolated from chrysanthemums (Section 26.4).

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Problem 64

Draw a stepwise mechanism for the following reaction.

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Problem 65

Acid-catalyzed hydrolysis of HOCH$_2$CH$_2$C(CH$_3$)$_2$CN forms compound $\textbf{A}$ (C$_6$H$_{10}$O$_2$). $\textbf{A}$ shows a strong peak in its IR spectrum at 1770 cm-1 and the following signals in its 1 H NMR spectrum: 1.27 (singlet, 6 H), 2.12 (triplet, 2 H), and 4.26 (triplet, 2 H) ppm. Draw the structure for $\textbf{A}$ and give a stepwise mechanism that accounts for its formation.

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Problem 66

What carboxylic acid and alcohol are needed to prepare each ester by Fischer esterification?

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Problem 66

What carboxylic acid and alcohol are needed to prepare each ester by Fischer esterification?

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Problem 67

Devise a synthesis of each compound using 1-bromobutane (CH$_3$CH$_2$CH$_2$CH$_2$Br) as the only organic starting material. You may use any other inorganic reagents.

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Problem 68

Convert 1-bromohexane (CH$_3$CH$_2$CH$_2$CH$_2$CH$_2$CH$_2$Br) into each compound. More than one step is required. You may use any other organic or inorganic reagents.
a. CH$_3$CH$_2$CH$_2$CH$_2$CH$_2$CH$_2$COCI
c. CH$_3$CH$_2$CH$_2$CH$_2$CH$_2$CH$_2$COCH$_3$
b. CH$_3$CH$_2$CH$_2$CH$_2$CH$_2$CH$_2$CO$_2$CH$_2$CH$_3$
d. CH$_3$CH$_2$CH$_2$CH$_2$CH$_2$CH$_2$CH$_2$NHCOCH$_3$

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Problem 69

Two methods convert an alkyl halide into a carboxylic acid having one more carbon atom. Depending on the structure of the alkyl halide, one or both of these methods may be employed. For each alkyl halide, write out a stepwise sequence that converts it to a carboxylic acid with one more carbon atom. If both methods work, draw both routes. If one method cannot be used, state why it can't.

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Problem 70

Devise a synthesis of benzocaine, ethyl $p$-aminobenzoate (H$_2$NC$_6$H$_4$CO$_2$CH$_2$CH$_3$), from benzene, organic alcohols, and any needed organic or inorganic reagents. Benzocaine is the active ingredient in the topical anesthetic Orajel (Section 18.15C).

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Problem 71

Devise a synthesis of melatonin, the mammalian hormone involved in regulating the sleep-wake cycle, from the neurotransmitter serotonin, alcohols, and any needed organic and inorganic reagents.

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Problem 72

Devise a synthesis of each analgesic compound from phenol (C$_6$H$_5$0H) and any other organic or inorganic reagents.

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Problem 73

Devise a synthesis of each compound from benzene and organic alcohols containing four or fewer carbons. You may also use any required organic or inorganic reagents.

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Problem 74

Devise a synthesis of each ester from benzene, organic alcohols, and any other needed inorganic reagents.

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Problem 75

Devise a synthesis of each labeled compound using H$_2$$^{18}$O and CH$_3$$^{13}$CH$_2$OH as the only sources of labeled starting materials. You may use any other unlabeled organic compounds and inorganic reagents.

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Problem 76

What polyester or polyamide can be prepared from each pair of monomers?

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Problem 77

What two monomers are needed to prepare each polymer?

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Problem 78

Taxotere is the trade name for the synthetic anticancer drug docetaxel, whose structure closely resembles the naturally occurring compound taxol, which is isolated from the Pacific yew tree (Section 5.5).
a. Taxol's limited water solubility led to an extensive search for related compounds with increased water solubility. What structural features give docetaxel a better water solubility profile?
b. Docetaxel contains a carbamate (labeled in red), a functional group with a carbonyl group bonded to a nitrogen and oxygen atom. Draw three more resonance structures for a carbamate (in addition to the Lewis structure with all neutral atoms given). Rank all four resonance structures in order of increasing stability.
c. A carbamate with a $\textit{tert}$-butoxy group [(CH$_3$)$_3$CO$^-$] is hydrolyzed according to the given equation. Draw a stepwise mechanism for the hydrolysis of a carbamate to the three products shown.
d. Assuming that all ester and carbamate bonds are cleaved, draw all products formed when docetaxel is hydrolyzed with aqueous acid.

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Problem 79

How can IA spectroscopy be used to distinguish between each pair of isomers?

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Problem 80

Rank the compounds in each group in order of increasing frequency of the C = O absorption in their IR spectra.

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Problem 81

Identify the structures of each compound from the given data.
a. Molecular formula C$_5$H$_{12}$O$_2$
IA absorption: 1738 cm$^{-1}$
$^1$H NMR: 1.12 (triplet, 3 H), 1.23 (doublet, 6 H), 2.28 (quartet, 2 H), and 5.00 (septet, 1 H) ppm
b. Molecular formula C$_4$H$_7$N
IR absorption: 2250 cm$^{-1}$
$^1$H NMR: 1.08 (triplet, 3 H), 1.70 (multiplet, 2 H), and 2.34 (triplet, 2 H) ppm
c. Molecular formula C$_8$H$_9$NO
IA absorptions: 3328 and 1639 cm$^{-1}$
$^1$H NMR: 2.95 (singlet, 3 H), 6.95 (singlet, 1 H), and 7.3-7.7 (multiplet, 5 H) ppm
d. Molecular formula C$_4$H$_7$CIO
IA absorption: 1802 cm$^{-1}$
$^1$H NMA: 0.95 (triplet, 3 H), 1.07 (multiplet, 2 H), and 2.90 (triplet, 2 H) ppm
e. Molecular formula C$_5$H$_{10}$O$_2$
IA absorption: 1750 cm$^{-1}$
$^1$H NMA: 1.20 (doublet, 6 H), 2.00 (singlet, 3 H), and 4.95 (septet, 1 H) ppm
f. Molecular formula C$_{10}$H$_{12}$O$_2$
IA absorption: 1740 cm$^{-1}$
$^1$H NMA: 1.2 (triplet, 3 H), 2.4 (quartet, 2 H), 5.1 (singlet, 2 H), and 7.1-7.5 (multiplet, 5 H) ppm
g. Molecular formula C$_8$H$_{14}$O$_3$
IA absorptions: 1810 and 1770 cm$^{-1}$
$^1$H NMA: 1.25 (doublet, 12 H) and 2.65 (septet, 2 H) ppm

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Problem 82

Identify the structures of $\textbf{A}$ and $\textbf{B}$, isomers of molecular formula C$_{10}$H$_{12}$O$_2$, from their IR data and $^1$H NMR spectra.
a. IR absorption for $\textbf{A}$ at 1718 cm$^{-1}$
b. IR absorption for $\textbf{B}$ at 17 40 cm$^{-1}$

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Problem 83

Phenacetin is an analgesic compound having molecular formula C$_{10}$H$_{13}$NO$_2$. Once a common component in over-the-counter pain relievers such as APC (aspirin, phenacetin, caffeine), phenacetin is no longer used because of its liver toxicity. Deduce the structure of phenacetin from its $^1$H NMA and IA spectra.

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Problem 84

Identify the structure of compound C (molecular formula C$_{11}$H$_{15}$NO$_2$), which has an IR absorption at 1699 cm$^{-1}$ and the $^1$H NMR spectrum shown below.

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Problem 85

Identify the structures of $\textbf{D}$ and $\textbf{E}$, isomers of molecular formula C$_6$H$_{12}$O$_2$, from their IR and $^1$H NMR data. Signals at 1.35 and 1.60 ppm in the $^1$H NMR spectrum of $\textbf{D}$ and 1.90 ppm in the $^1$H NMR spectrum of $\textbf{E}$ are multiplets.
a. IR absorption for $\textbf{D}$ at 1743 cm$^{-1}$
b. IR absorption for $\textbf{E}$ at 17 46 cm$^{-1}$

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Problem 86

With reference to amides $\textbf{A}$ and $\textbf{B}$, the carbonyl of one amide absorbs at a much higher wavenumber in its IR spectrum than the
carbonyl of the other amide. Which absorbs at higher wavenumber and why?

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Problem 87

The $^1$H NMR spectrum of 2-chloroacetamide (CICH$_2$CONH$_2$) shows three signals at 4.02, 7.35, and 7.60 ppm. What protons give rise to each signal? Explain why three signals are observed.

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Problem 88

Compelling evidence for the existence of a tetrahedral intermediate in nucleophilic acyl substitution was obtained in a series of elegant experiments carried out by Myron Bender in 1951. The key experiment was the reaction of aqueous $^-$OH with ethyl benzoate (C$_6$H$_5$COOCH$_2$CH$_3$) labeled at the carbonyl oxygen with $^{18}$O. Bender did not allow the hydrolysis to go to completion, and then examined the presence of a label in the $\textit{recovered starting material}$. He found that some of the recovered ethyl benzoate no longer contained a label at the carbonyl oxygen. With reference to the accepted mechanism of nucleophilic acyl substitution, explain how this provides evidence for a tetrahedral intermediate.

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Problem 89

Draw a stepwise mechanism for the following reactions, two steps in R. B. Woodward's classic synthesis of reserpine in 1958. Reserpine, which is isolated from the extracts of the Indian snakeroot $\textit{Rauwolfia serpentina Benth}$, was used at one time to manage mild hypertension associated with anxiety.

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Problem 90

Draw a stepwise mechanism for the following reaction, the last step in a five-step industrial synthesis of vitamin C that begins with the simple carbohydrate glucose.

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Problem 91

Draw a stepwise mechanism for the following reaction, a key step in the synthesis of linezolid, an antibacterial agent.

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