Organic Chemistry

Janice Gorzynski Smith

Chapter 28

Carbohydrates

Educators

GY
LC

Problem 1

Draw the structure of (a) a ketotetrose; (b) an aldopentose; (c) an aldotetrose.

Check back soon!

Problem 2

Draw each stereogenic center using a Fischer projection formula.

Check back soon!

Problem 3

Label each stereogenic center as $R$ or $S.$

Ly T.
Numerade Educator

Problem 4

Convert the ball-and-stick model to a Fischer projection.

Check back soon!

Problem 5

Assign $R,S$ designations to each stereogenic center in glucose.

Ly T.
Numerade Educator

Problem 6

(a) Label compounds $\textbf{A}$, $\textbf{B}$, and $\textbf{C}$ as $\small\mathrm{D}$- or $\small\mathrm{L}$-sugars. (b) How are compounds $\textbf{A}$ and $\textbf{B}$ related? $\textbf{A}$ and $\textbf{C?}$ $\textbf{B}$ and $\textbf{C?}$ Choose from enantiomers, diastereomers, or constitutional isomers.

Check back soon!

Problem 7

How many different aldoheptoses are there? How many are $\small\mathrm{D}$-sugars? Draw all $\small\mathrm{D}$-aldoheptoses having the $R$ configuration at C2 and C3.

Ly T.
Numerade Educator

Problem 8

Draw two possible epimers of $\small\mathrm{D}$-erythrose. Name each of these compounds using Figure 28.4.

Check back soon!

Problem 9

Referring to the structures in Figures 28.4 and 28.5, classify each pair of compounds as
enantiomers, epimers, diastereomers but not epimers, or constitutional isomers of each other.
a. $\small\mathrm{D}$-allose and $\small\mathrm{L}$-allose
b. $\small\mathrm{D}$-altrose and $\small\mathrm{D}$-gulose
c. $\small\mathrm{D}$-galactose and $\small\mathrm{D}$-talose
d. $\small\mathrm{D}$-mannose and $\small\mathrm{D}$-fructose
e. $\small\mathrm{D}$-fructose and $\small\mathrm{D}$-sorbose
f. $\small\mathrm{L}$-sorbose and $\small\mathrm{L}$-tagatose

Ly T.
Numerade Educator

Problem 10

a. Draw the enantiomer of $\small\mathrm{D}$-fructose.
b. Draw an epimer of $\small\mathrm{D}$-fructose at C4. What is the name of this compound?
c. Draw an epimer of $\small\mathrm{D}$-fructose at CS. What is the name of this compound?

Check back soon!

Problem 11

Referring to Figure 28.5, which $\small\mathrm{D}$-ketohexoses have the $S$ configuration at C3?

Check back soon!

Problem 12

Convert each aldohexose to the indicated anomer using a Haworth projection.

Sourav K.
Numerade Educator

Problem 13

Convert each Haworth projection to its acyclic form.

Ly T.
Numerade Educator

Problem 14

Convert each Haworth projection in Problem 28.13 to a three-dimensional representation using a
chair pyranose ring.

Check back soon!

Problem 15

Aldotetroses exist in the furanose form. Draw both anomers of $\small\mathrm{D}$-erythrose.

Ly T.
Numerade Educator

Problem 16

What glycosides are formed when each monosaccharide is treated with CH$_3$CH$_2$OH, HCI:
(a) $\beta$-$\small\mathrm{D}$-mannose; (b) $\alpha$-$\small\mathrm{D}$-gulose; (c) $\beta$-$\small\mathrm{D}$-fructose?

Check back soon!

Problem 17

Draw a stepwise mechanism for the following reaction.

Ly T.
Numerade Educator

Problem 18

(a) Label all the O atoms that are part of a glycoside in rebaudioside A. Rebaudioside A, marketed
under the trade name Truvia, is a sweet glycoside obtained from the stevia plant, which has been used for centuries in Paraguay to sweeten foods. (b) The alcohol or phenol formed from the hydrolysis of a qlycoside is called an aglycon. What $\textbf{aglycon}$ and monosaccharides are formed by the hydrolysis of rebaudioside A?

Check back soon!

Problem 19

Draw the products formed when $\beta$-$\small\mathrm{D}$-galactose is treated with each reagent.
a. Ag$_2$O + CH$_3$I
b. NaH + C$_6$H$_5$CH$_2$CI
c. The product in (b), then H$_3$O$^+$
d. Ac$_2$O + pyridine
e. C$_6$H$_5$COCI + pyridine
f. The product in (c), then C$_6$H$_5$COCI + pyridine

Ly T.
Numerade Educator

Problem 20

A 2-ketohexose is reduced with NaBH$_4$ in CH$_3$OH to form a mixture of $\small\mathrm{D}$-galactitol and $\small\mathrm{D}$-talitol. What is the structure of the 2-ketohexose?

Check back soon!

Problem 21

Classify each compound as a reducing or nonreducing sugar.

Ly T.
Numerade Educator

Problem 22

Draw the products formed when $\small\mathrm{D}$-arabinose is treated with each reagent: (a) Ag$_2$O, NH$_4$OH; (b) Br$_2$, H$_2$O; (c) HNO$_3$ , H$_2$O.

Check back soon!

Problem 23

Which aldoses are oxidized to optically inactive aldaric acids: (a) $\small\mathrm{D}$-erythrose; (b) $\small\mathrm{D}$-lyxose; (c) $\small\mathrm{D}$-galactose?

Ly T.
Numerade Educator

Problem 24

What two aldoses yield $\small\mathrm{D}$-xylose on Wohl degradation?

Check back soon!

Problem 25

What aldoses are formed when the following aldoses are subjected to the Kiliani-Fischer synthesis: (a) $\small\mathrm{D}$-threose; (b) $\small\mathrm{D}$-ribose; (c) $\small\mathrm{D}$-galactose?

Ly T.
Numerade Educator

Problem 26

D-Aldopentose $\textbf{A}$ is oxidized to an optically inactive aldaric acid. On Wohl degradation, $\textbf{A}$ forms an aldotetrose $\textbf{B}$ that is oxidized to an optically active aldaric acid. What are the structures of $\textbf{A}$ and $\textbf{B?}$

GY
Ginger Y.
Numerade Educator

Problem 27

Besides $\small\mathrm{D}$-mannose, only one other $\small\mathrm{D}$-aldohexose yields itself when the CHO and CH$_2$OH groups on the end carbon atoms are interchanged. What is the name and structure of this $\small\mathrm{D}$-aldohexose?

Ly T.
Numerade Educator

Problem 28

A $\small\mathrm{D}$-aldohexose $\textbf{A}$ is formed from an aldopentose $\textbf{B}$ by the Kiliani$-$Fischer synthesis. Reduction of $\textbf{A}$ with NaBH$_4$ forms an optically inactive alditol. Oxidation of $\textbf{B}$ forms an optically active aldaric acid. What are the structures of $\textbf{A}$ and $\textbf{B}$?

Check back soon!

Problem 37

Convert each ball-and-stick model to a Fischer projection.

Ly T.
Numerade Educator

Problem 38

(a) Convert each cyclic monosaccharide into a Fischer projection of its acyclic form. (b) Name each monosaccharide. (c) Label the anomer as $\alpha$ or $\beta$.

Check back soon!

Problem 39

Classify each compound as identical to $\textbf{A}$ or its enantiomer.

Ly T.
Numerade Educator

Problem 40

Convert each compound to a Fischer projection and label each stereogenic center as $R$ or $S$.

Check back soon!

Problem 41

Draw the C4 epimer of $\textbf{D}$-xylose and name the monosaccharide.

Ly T.
Numerade Educator

Problem 42

For $\small\mathrm{D}$-arabinose:

a. Draw its enantiomer.
b. Draw an epimer at C3.
c. Draw a diastereomer that is not an epimer.
d. Draw a constitutional isomer that still contains a carbonyl group.

Check back soon!

Problem 43

Consider the following six compounds ($\textbf{A-F}$).
How are the two compounds in each pair related? Choose from enantiomers, epimers, diastereomers but not epimers, constitutional isomers, and identical compounds.
a. $\textbf{A}$ and $\textbf{B}$
b. $\textbf{A}$ and $\textbf{C}$
c. $\textbf{B}$ and $\textbf{C}$
d. $\textbf{A}$ and $\textbf{D}$
e. $\textbf{E}$ and $\textbf{F}$

Ly T.
Numerade Educator

Problem 44

Consider the monosaccharide aldopentoses $\textbf{A}$ and $\textbf{B,}$, drawn below.
a. Which of the following terms describe $\textbf{A}$ and $\textbf{B:}$ epimers, anomers, enantiomers, diastereomers, and reducing sugars?
b. Draw the acyclic form of both $\textbf{A}$ and $\textbf{B,}$ and name each compound.

LC
Laura C.
Numerade Educator

Problem 45

Draw a Haworth projection for each compound using the structures in Figures 28.4 and 28.5.
a. $\beta$-$\small\mathrm{D}$-talopyranose
b. $\beta$-$\small\mathrm{D}$-mannopyranose
c. $\alpha$-$\small\mathrm{D}$-galactopyranose
d. $\alpha$-$\small\mathrm{D}$-ribofuranose
e. $\alpha$-$\small\mathrm{D}$-tagatofuranose

Ly T.
Numerade Educator

Problem 46

Draw both pyranose anomers of each aldohexose using a three-dimensional representation with a chair pyranose. Label each anomer as $\alpha$ or $\beta$.

Check back soon!

Problem 47

Convert each cyclic monosaccharide into its acyclic form.

Ly T.
Numerade Educator

Problem 48

$\small\mathrm{D}$-Arabinose can exist in both pyranose and furanose forms.
a. Draw the $\alpha$ and $\beta$ anomers of $\small\mathrm{D}$-arabinofuranose.
b. Draw the $\alpha$ and $\beta$ anomers of $\small\mathrm{D}$-arabinopyranose.

Check back soon!

Problem 49

The most stable conformation of the pyranose ring of most $\small\mathrm{D}$-aldohexoses places the largest group, CH$_2$OH, in the equatorial position. An exception to this is the aldohexose $\small\mathrm{D}$-idose. Draw the two possible chair conformations of either the $\alpha$ or $\beta$ anomer of $\small\mathrm{D}$-idose. Explain why the more stable conformation has the CH$_2$OH group in the axial position.

Ly T.
Numerade Educator

Problem 50

Draw the products formed when a-o-gulose is treated with each reagent.

Check back soon!

Problem 51

Draw the products formed when $\small\mathrm{D}$-altrose is treated with each reagent.

Ly T.
Numerade Educator

Problem 52

What aglycon and monosaccharides are formed when salicin and solanine (Section 28.?C) are each hydrolyzed with aqueous acid?

Check back soon!

Problem 53

What two aldohexoses yield D-arabinose upon Wohl degradation?

Ly T.
Numerade Educator

Problem 54

What products are formed when each compound is subjected to a Kiliani-Fischer synthesis?

Check back soon!

Problem 55

How would you convert o-glucose into each compound? More than one step is required.

Ly T.
Numerade Educator

Problem 56

Which $\small\mathrm{D}$-aldopentoses are reduced to optically inactive alditols using NaBH$_4$, CH$_3$OH?

Check back soon!

Problem 57

What products are formed when each compound is treated with aqueous acid?

Ly T.
Numerade Educator

Problem 58

Draw a stepwise mechanism for the acid-catalyzed interconversion of two glucose anomers by mutarotation.

Check back soon!

Problem 59

Draw a stepwise mechanism for the following reaction.

Ly T.
Numerade Educator

Problem 60

Draw a stepwise mechanism for the following hydrolysis.

Check back soon!

Problem 61

In the oxidation of o-allose to o-allonic acid, a lactone having the general structure $\textbf{A}$ is isolated. Draw a stepwise mechanism to account for the formation of $\textbf{A}$. Use wedges and dashes to indicate the stereochemistry of all stereogenic centers in $\textbf{A}$.

Ly T.
Numerade Educator

Problem 62

The following isomerization reaction, drawn using D-glucose as starting material, occurs with all aldohexoses in the presence of base. Draw a stepwise mechanism that illustrates how each compound is formed.

Check back soon!

Problem 63

Which D-aldopentose is oxidized to an optically active aldaric acid and undergoes the Wohl degradation to yield a D-aldotetrose that is oxidized to an optically active aldaric acid?

Ly T.
Numerade Educator

Problem 64

What other D-aldopentose forms the same alditol as D-arabinose when reduced with NaBH$_4$ in CH$_3$OH?

Check back soon!

Problem 65

Identify compounds $\textbf{A-D.}$ A D-aldopentose $\textbf{A}$ is oxidized with HNO$_3$ to an optically inactive aldaric acid $\textbf{B.}$ $\textbf{A}$ undergoes the Kiliani$-$Fischer synthesis to yield $\textbf{C}$ and $\textbf{D.}$ $\textbf{C}$ is oxidized to an optically active aldaric acid. $\textbf{D}$ is oxidized to an optically inactive aldaric acid.

Ly T.
Numerade Educator

Problem 66

A D-aldopentose $\textbf{A}$ is reduced to an optically active alditol. Upon Kiliani$-$Fischer synthesis, $\textbf{A}$ is converted to two D-aldohexoses, $\textbf{B}$ and $\textbf{C.}$ $\textbf{B}$ is oxidized to an optically inactive aldaric acid. $\textbf{C}$ is oxidized to an optically active aldaric acid. What are the structures of $\textbf{A-C?}$

Check back soon!

Problem 67

A D-aldohexose $\textbf{A}$ is reduced to an optically active alditol $\textbf{B}$ using NaBH$_4$ in CH$_3$OH. $\textbf{A}$ is converted by Wohl degradation to an aldopentose $\textbf{C,}$ which is reduced to an optically inactive alditol $\textbf{D.}$ $\textbf{C}$ is converted by Wohl degradation to aldotetrose $\textbf{E,}$ which is oxidized to an optically active aldaric acid $\textbf{F.}$ When the two ends of aldohexose $\textbf{A}$ are interconverted, a different aldohexose $\textbf{G}$ is obtained. What are the structures of $\textbf{A-G?}$

Ly T.
Numerade Educator

Problem 68

Draw the structure of a disaccharide formed from two galactose units joined by a 1$\rightarrow$4-$\beta$-glycosidic linkage.

Brian J.
Numerade Educator

Problem 69

Draw the structure of a disaccharide formed from two mannose units joined by a 1$\rightarrow$4-$\alpha$-glycosidic linkage.

Ly T.
Numerade Educator

Problem 70

Identify the lettered compounds in the following reactions.

Check back soon!

Problem 71

For each disaccharide in Problem 28.70:
a. Identify the glycosidic linkage.
b. Classify the glycosidic bond as $\alpha$ or $\beta$ and use numbers to designate its location.
c. Classify each disaccharide as reducing or nonreducing.

Check back soon!

Problem 72

Consider the tetrasaccharide stachyose drawn below. Stachyose is found in white jasmine, soybeans, and lentils. Because humans cannot digest it, its consumption causes flatulence.
a. Label all glycoside bonds.
b. Classify each glycosidic linkage as $\alpha$ or $\beta$ and use numbers to designate its location between two rings (e.g., 1$\rightarrow$4-$\beta$)-
c. What products are formed when stachyose is hydrolyzed with H$_3$O$^+$?
d. Is stachyose a reducing sugar?
e. What product is formed when stachyose is treated with excess CH$_3$I, Ag$_2$O?
f. What products are formed when the product in (e) is treated with H$_3$O$^+$?

Check back soon!

Problem 73

Deduce the structure of the disaccharide isomaltose from the following data.
[1] Hydrolysis yields D-glucose exclusively.
[2] lsomaltose is cleaved with $\alpha$-glycosidase enzymes.
[3] lsomaltose is a reducing sugar.
[4] Methylation with excess CH$_3$I, Ag$_2$O and then hydrolysis with H$_3$O$^+$ forms two products:

Ly T.
Numerade Educator

Problem 74

Deduce the structure of the disaccharide trehalose from the following data. Trehalose is the "blood sugar" of the insect world. It is found in bacterial spores, fungi, and many insects whose natural environment has large variations in temperature.
[1] Hydrolysis yields D-glucose exclusively.
[2] Trehalose is hydrolyzed by $\alpha$-glycosidase enzymes.
[3] Trehalose is a nonreducing sugar.
[4] Methylation with excess CH$_3$I, Ag$_2$O, followed by hydrolysis with H$_3$O$^+$, forms only one product:

Check back soon!

Problem 75

Draw the structure of each of the following compounds:
a. a polysaccharide formed by joining D-glucosamine in 1$\rightarrow$6-$\alpha$-glycosidic linkages
b. a disaccharide formed by joining D-mannose and D-glucose in a 1$\rightarrow$4-$\beta$-glycosidic linkage using mannose's anomeric carbon
c. an $\alpha$-$N$-glycoside formed from D-arabinose and C$_6$H$_5$CH$_2$NH$_2$
d. a ribonucleoside formed from D-ribose and thymine

Ly T.
Numerade Educator

Problem 76

(a) Draw the more stable chair form of fucose, an essential monosaccharide needed in the diet and a component of carbohydrates on mammalian and plant cell surfaces. (b) Classify fucose as a D- or L-monosaccharide. (c) What two structural features are unusual in fucose?

Check back soon!

Problem 77

As we have seen in Chapter 28, monosaccharides can be drawn in a variety of ways, and in truth, often a mixture of cyclic compounds is present in a solution. Identify each monosaccharide, including its proper D,L designation, drawn in a less-thantypical
fashion.

Check back soon!

Problem 78

Draw a stepwise mechanism for the following reaction.

Check back soon!

Problem 79

Deduce the structure of the trisaccharide ($\textbf{X}$) from the given information.
[1] Methylation with excess CH$_3$I, Ag$_2$O and then hydrolysis with H$_3$O$^+$ forms three products.
[2] $\textbf{X}$ is cleaved with a $\beta$-glycosidase enzyme to give a disaccharide and D-galactose.
[3] $\textbf{X}$ is cleaved with an $\alpha$-glycosidase enzyme to give a disaccharide and D-fructose.

Ly T.
Numerade Educator