Organic Chemistry

T.W. Graham Solomons, Craig B. Fryhle, Scott A. Snyder

Chapter 22

Carbohydrates - all with Video Answers

Educators

Chapter Questions

Problem 1

How many chirality centers are contained in (a) the aldotctrose and (b) the ketopentose just given? (c) How many stereo-isomers would you expect from each general structure?

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 2

Write three-dimensional formulas for each aldotctrose and ketopentose isomer in Practice Problem 22.1 and designate each as a $\mathrm{D}$ or $\mathrm{L}$. sugar.

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 3

Draw the $\beta$ -pyranose form of (a) in its lowest energy chair conformation, and a Fischer projection for (b).
a.(FIGURE CAN'T COPY)
b.(FIGURE CAN'T COPY)

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 4

(a) What products would be formed if salicin were treated with dilute aqucous HCl?
(b) Outline a mechanism for the reactions involved in their formation.

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 5

How would you convert D-glucose to a mixture of ethyl $\alpha$ -p-glucopyranoside and ethyl $\beta$ -p-glucopyranoside? Show all steps in the mechanism for their formation.

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 6

How might you distinguish between $\alpha$ -p-glucopyranose (i.e., p-glucose) and methyl $\alpha$ -p-glucopyranoside?

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 7

(a) Would you expect p-glucaric acid to be optically active?
(b) Write the open-chain structure for the aldaric acid (mannaric acid) that would be obtained by nitric acid oxidation of D-man-nose.
(c) Would you expect mannaric acid to be optically active?
(d) What aldaric acid would you expect to obtain from perythrose?
(e) Would the aldaric acid in (d) show optical activity?
(f) D-Threose, a diastereomer of D-erythrocyte, yields an optically active aldaric acid when
it is subjected to nitric acid oxidation. Write Fischer projection formulas for D-threose and its nitric acid oxidation product.
(g) What are the names of the aldaric acids obtained from perythrose and p-threose?

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 8

p-Glucaric acid undergoes lactonization to yield two different $y$ -lactones. What are their structures?

Rashmi Sinha

Numerade Educator

Problem 9

What products would you expect to be formed when each of the following compounds is treated with an appropriate amount of periodic acid? How many molar equivalents of HIO $_{4}$ would be consumed in each case?
a.(FIGURE CAN'T COPY)
b.(FIGURE CAN'T COPY)
c.(FIGURE CAN'T COPY)
d.(FIGURE CAN'T COPY)
e.(FIGURE CAN'T COPY)
f.(FIGURE CAN'T COPY)
g.(FIGURE CAN'T COPY)
h.(FIGURE CAN'T COPY)

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 10

Show how periodic acid could be used to distinguish between an aldohcxose and a ketohexose. What products would you obtain from each, and how many molar equivalents of HIO $_{4}$ would be consumed?

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 11

(a) Would you expect p-glucitol to be optically active? (b) Write Fischer projection formulas for all of the $\mathbf{p}$ -aldohexoses that would yield optically inactive alditols.

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 12

Although D-fructose is not an epimer of D-glucose or $\mathrm{D}$ -mannose (D-fructose is a ketohexose), all three yield the same phenylosazone. (a) Using Fischer projection formulas, write an equation for the reaction of fructose with phenylhydrazine. (b) What information about the stereo-chemistry of $\mathrm{D}$ -fructose does this experiment yield?

Shubham Kumar

Numerade Educator

Problem 13

(a) What are the structures of $\mathrm{L}-(+)$ -threose and $\mathrm{i}-(+)$ -erythrose? (b) What aldotriose would you use to prepare them in a Kiliani-Fischer synthesis?

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 14

(a) Outline a Kiliani-Fischer synthesis of epimeric aldopentoses starting with D-(-)-erythrose (use Fischer projections). (b) The two epimeric aldopentoses that one obtains are $\mathrm{D}-(-)$ -arabinose and $\mathrm{D}-(-)$ -ribose. Nitric acid oxidation of $\mathrm{D}-(-)$ -ribose yields an optically inactive aldaric acid, whereas similar oxidation of $\mathrm{D}-(-)$ -arabinose yields an optically active product. On the basis of this information alone, which Fischer projection represents $\mathrm{D}-(-)$ -arabinose and which represents $\mathrm{D}-(-)$ -ribose?

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 15

Subjecting $\mathrm{D}-(-)$ -threose to a Kiliani-Fischer synthesis yields two other epimeric aldopentoses, $\mathrm{D}-(+)$ -xylose and $\mathrm{D}-(-)$ -lyxose. $\mathrm{D}-(+)$ - Xylose can be oxidized (with nitric acid) to an optically inactive aldaric acid, while similar oxidation of $\mathrm{D}-(-)$ -lyxose gives an optically active product. What are the structures of $\mathrm{D}-(+)$ -xylose and $\mathrm{D}-(-)$ -lyxose?

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 16

There are eight aldopentoses. In Practice Problems 22.14 and 22.15 you have arrived at the structures of four. What are the names and structures of the four that remain?

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 17

The aldohexose $\mathrm{D}-(+)$ -galactose can be obtained by hydrolysis of lactose, a disaccharide found in milk. When $\mathrm{D}-(+)$ -galactose is treated with nitric acid, it yields an optically inactive aldaric acid. When $\mathrm{D}-(+)$ - galactose is subjected to Ruff degradation, it yields D-(-)-lyxose (see Practice Problem 22.15 ). Using only these data, write the Fischer projection formula for $\mathrm{D}-(+)$ -galactose.

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 18

Fischer actually had to subject both $y$ -lactones of $\mathrm{D}$ -glucaric acid (Practice Problem 22.8 ) to the procedure just outlined. What product does the other $y$ -lactone yield?

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 19

Direct oxidation of an aldose affects the aldehyde group first, converting it to a carboxylic acid (Section $22.6 \mathrm{B}$ ), and most oxidizing agents that will attack $1^{\circ}$ alcohol groups will also attack $2^{\circ}$ alcohol groups. Clearly, then, a laboratory synthesis of a uronic acid from an aldose requires protecting these groups from oxidation. Keeping this in mind, suggest a method for carrying out a specific oxidation that would convert D-galactose to D-galacturonic acid. (Hint: See Section 22.5E.)

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 20

Give appropriate structural formulas to illustrate each of the following:
(in) Epimers
(q) A polysaccharide
$\begin{array}{lllll}\text { (b) A ketohexose } & \text { (f) An aldaric acid } & \text { (i) A reducing sugar } & \text { (n) Anomers } & \text { (r) A nonreducing sugar }\end{array}$
$\begin{array}{llll}\text { (a) An aldopentose } & \text { (e) An aldonic acid } & \text { (i) A furanose } & \text { (m) Epimers } \\ \text { (b) A ketohexose } & \text { (f) An aldaric acid } & \text { (i) A reducing sugar } & \text { (n) Anom } \\ \text { (c) An L-monosaccharide } & \text { (g) An aldonolactone } & \text { (k) A pyranoside } & \text { (o) } \\ \text { (d) A glycoside } & \text { (h) A pyranose } & \text { (I) A furanoside } & \text { (p) A disacchas }\end{array}$
(o) A phenyloszane

Maryam Riaz

Numerade Educator

Problem 21

Draw conformational formulas for cach of the following: (a) $\alpha$ -D-allopyranose, ( b) methyl $\beta$ -D-allopyranoside, and (c) methyl 2,3,4,6 -tetra- $Q$ -methyl- $\beta$ -p-allopyranoside.

Allison Krajewski

Allison Krajewski

Numerade Educator

Problem 22

Draw structures for furanose and pyranose forms of D-ribose. Show how you could use periodate oxidation to distinguish between a methyl ribofuranoside and a methyl ribopyranoside.

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 23

One reference book lists $\mathrm{D}$ -mannose as being dextrorotatory; another lists it as being levorotatory. Both references are correct. Explain.

Brenda Sanchez

Numerade Educator

Problem 24

The starting material for a commercial synthesis of vitamin $C$ is 1 -sorbose (see the following reaction); it can be synthesized from p-glucose through the following reaction sequence: (FIGURE CAN'T COPY)
The second step of this sequence illustrates the use of a bacterial oxidation; the microorganism $A$, suboxydans accomplishes this step in 90\% yicld. The overall result of the synthesis is the transformation of a D-aldohexose (D-glucosc) into an I-ketohexose ( I-sorbose). What docs this mean about the specificity of the bacterial oxidation?

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 25

What two aldoses would yield the same phenylosazone as $1 \text { -sorbose (Problem } 22.24) ?$

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 26

In addition to fructose (Practice Problem 22.12 ) and sorbose (Problem 22.24 ), there are two other 2 -ketohexoses, psicose and tagatose. D-Psicose yields the same phenylosazone as $\mathrm{D}$ -allose (or D-altrose); D-tagatose yiclds the same osazone as $\mathrm{D}$ -galactose (or D-talose). What are the structures of D-psicose and D-tagatose?

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 27

A, B, and C are three aldohexoses. Compounds A and B yield the same optically active alditol when they are reduced with hydrogen and a caralyst; A and B yield different phenylosazones when treated with phenylhydrazine; B and C give the same phenylosazone but different alditols. Assuming that all are $\mathrm{D}$ sugars, give names and structures for $\mathbf{A}, \mathbf{B},$ and $\mathbf{C}$.0

Shazia Naz

Numerade Educator

Problem 28

Xylitol is a sweetener that is used in sugarless chewing gum. Starting with an appropriate monosaccharide, outline a possible synthesis of xylitol. (FIGURE CAN'T COPY)

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 29

Although monosaccharides undergo complex isomerizations in base (see Section $22.5 \mathrm{A}$ ), aldonic acids are epimerized specifically at C2 when they are heated with pyridine. Show how you could make use of this reaction in a synthesis of D-mannose from D-glucose.

Dalton Hilovsky

Dalton Hilovsky

Numerade Educator

Problem 30

The most stable conformation of most aldopyranoses is one in which the largest group, the $-\mathrm{CH}_{2} \mathrm{OH}$ group, is equatorial. However, p-idopyranose exists primarily in a conformation with an axial $-\mathrm{CH}_{2} \mathrm{OH}$ group. Write formulas for the two chair conformations of $\alpha$ -D-idopyranose (one with the $-\mathrm{CH}_{2} \mathrm{OH}$ group axial and one with the $-\mathrm{CH}_{2} \mathrm{OH}$ group equatorial) and provide an explanation.

Ly Tran

Numerade Educator

Problem 31

(a) Heating p-altrose with dilute acid produces a nonreducing anbydro sugar (C $_{6} \mathrm{H}_{10} \mathrm{O}_{5}$ ). Methylation of the anhydro sugar followed by acid hydrolysis yiclds 2,3,4 -tri- $Q$ -methyl-p-altrose. The formation of the anhydro sugar takes place through a chair conformation of $\beta$ -D-altropyranose in which the $-\mathrm{CH}_{2} \mathrm{OH}$ group is axial. What is the structure of the anhydro sugar, and how is it formed? (b) p-Glucose also forms an anhydro sugar but the conditions required are much more drastic than for the corresponding reaction of D-altrose. Explain.

Ian Kaigh

Numerade Educator

Problem 32

Show how the following experimental evidence can be used to deduce the structure of lactose (Section $22.12 \mathrm{D}$ ) :
1. Acid hydrolysis of lactose $\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right)$ gives equimolar quantitics of D-glucose and D-galactose. Lactose undergocs a similar hydrolysis
in the presence of a $\beta$ -galactosidase.
2. Lactose is a reducing sugar and forms a phenylosazone; it also undergoes mutarotation.
3. Oxidation of lactose with bromine water followed by hydrolysis with dilute acid gives $\mathbf{p}$ -galactose and $\mathbf{p}$ -gluconic acid.
4. Bromine water oxidation of lactose followed by methylation and hydrolysis gives 2,3,6 -tri- $O$ -methylgluconolactone and 2,3,4,6 -terra- $O$ -methyl-p-galactose.
5. Methylation and hydrolysis of lactose give 2,3,6 -tri- $Q$ -methyl-p-glucose and 2,3,4,6 -terra- $Q$ -methyl-p.galactose.

Zubair Abdulla

Numerade Educator

Problem 33

Deduce the structure of the disaccharide melibiose from the following data:
1. Melibiose is a reducing sugar that undergoes mutarotation and forms a phenylosazone.
2. Hydrolysis of melibiose with acid or with an $\alpha$ -galactosidase gives $\mathrm{p}$ -galactose and $\mathrm{p}$ -glucose.
3. Bromine water oxidation of melibiose gives melibionic acid. Hydrolysis of melibionic acid gives D-galactose and D-gluconic acid. Methylation of melibionic acid followed by hydrolysis gives 2,3,4,6 -tetra- $Q$ -methy-p-galactose and 2,3,4,5 -terra- $Q$ -methyl-p.gluconic acid.

Ronald Prasad

Numerade Educator

Problem 34

Trehalose is a disaccharide that can be obtained from yeasts, fungi, sea urchins, algae, and insects. Deduce the structure of trehalose from the following information:
1. Acid hydrolysis of trehalose yields only b-glucose.
2. Trehalose is hydrolyzed by $\alpha$ -glucosidase but not by $\beta$ -glucosidase enzymes.
3. Trehalose is a nonreducing sugar; it does not mutarotate, form a phenylosazone, or react with bromine water.
4. Methylation of trehalose followed by hydrolysis yields two molar equivalents of 2,3,4,6 -terra- $Q$ -methyl-p-glucose.

Shazia Naz

Numerade Educator

Problem 35

Outline chemical tests that will distinguish between members of each of the following pairs:
(a) D-Glucose and D-glucitol
(b) D-Glucitol and D-glucaric acid
(c) D-Glucose and $\mathbf{p}$ -fructose
(d) D-Glucose and D-galactose
(e) Sucrose and maltose
(f) Maltose and maltonic acid
(g) Methyl $\beta$ -D-glucopyranoside and 2,3,4,6 -tetra- $O$ -methyl- $\beta$ -D-glucopyranose
(h) Methyl $\alpha$ -D-ribofuranoside (I) and methyl 2 -deoxy- $\alpha$ -Dribofuranoside ( $\mathbf{I I}$ ):
(FIGURE CAN'T COPY)

Ronald Prasad

Numerade Educator

Problem 36

A group of oligosaccharides called Schardinger dextrins can be isolated from Bacillus macenans when the bacillus is grown on a medium rich in amylose. These oligosaccharides are all nonreducing. A typical Schardinger dextrin undergoes hydrolysis when treated with an acid or an $\alpha$ -glucosidase to yicld six, scren, or cight molecules of D-glucosse. Complete methylation of a Schardingcr dextrin followed by acid hydrolysis yields only 2,3,6 -tri- $O$ -methyl-p-glucose. Propose a general structure for a Schardinger dextrin.

Narayan Hari

Numerade Educator

Problem 37

Isomalose is a disaccharide that can be obtained by enzymatic hydrolysis of amylopectin. Deduce the structure of isomaltose from the following data:
1. Hydrolysis of 1 mol of isomaltose by acid or by an $\alpha$ -glucosidase gives 2 mol of $\mathrm{D}$ -glucose.
2. Isomaltose is a reducing sugar.
3. Isomaltose is oxidized by bromine water to isomaltonic acid. Methylation of isomaltonic acid and subsequent hydrolysis yields 2,3,4,6 -tetra- $Q$ -methyl-p-glucose and 2,3,4,5 -tetra- $Q$ -methyl-p-gluconic acid.

Ly Tran

Numerade Educator

Problem 38

Stachyose occurs in the roots of several species of plants. Deduce the structure of stachyose from the following data:
1. Acidic hydrolysis of 1 mol of stachyose yields 2 mol of D-galactose, 1 mol of $\mathrm{D}$ -glucose, and 1 mol of $\mathrm{D}$ -fructose.
2. Stachyose is a nonreducing sugar.
3. Treating stachyose with an $\alpha$ -galactosidase produces a mixture containing p-galactose, sucrose, and a nonreducing trisaccharide called raffinose.
4. Acidic hydrolysis of raffinose gives p-glucose, p-fructose, and p-galactose. Treating raffinose with an $\alpha$ -galactosidase yields p-galactose and sucrose. Treating raffinose with invertase (an enzyme that hydrolyzes sucrose) yields fructose and melibiose (see Problem 22.33 ).
5. Methylation of stachyose followed by hydrolysis yiclds 2,3,4,6 -tetra- $Q$ -methyl-p-galactose, 2,3,4 -tri- $Q$ -methyl-p-galactose, 2,3,4 -tri- $Q$ -methyl-p-glucosce, and 1,3,4,6 -tetra- $Q$ -methyl-p-fructose.

Jennifer Hudspeth

Jennifer Hudspeth

Numerade Educator

Problem 39

Arbutin, a compound that can be isolated from the leaves of barberry, cranberry, and pear trees, has the molecular formula $\mathrm{C}_{12} \mathrm{H}_{16} \mathrm{O}_{7} .$ When arbutin is treated with aqueous acid or with a $\beta$ -glucosidase, the reaction produces $\mathrm{D}$ -glucose and a compound $\mathrm{X}$ with the molecular formula $\mathrm{C}_{6} \mathrm{H}_{6} \mathrm{O}_{2}$. The 'H NMR spectrum of compound $\mathrm{X}$ consists of two singlets, one at $\delta 6.8(4 \mathrm{H})$ and one at $\delta 7.9(2 \mathrm{H}) .$ Methylation of arbutin followed by acidic hydrolysis yiclds 2,3,4,6 -tetra- $Q$ -methyl-p-glucoss and a compound $\mathbf{Y}\left(\mathrm{C}_{7} \mathrm{H}_{8} \mathrm{O}_{2}\right) .$ Compound
Y is soluble in dilute aqueous NaOH but is insoluble in aqueous NaHCO, The 'H NMR spectrum of Y shows a singlet at $\delta 3.9(3 \mathrm{H}),$ a singler at $\delta 4.8(1 \mathrm{H}),$ and a multiplet (that resembles a singlet) at $\delta 6.8(4 \mathrm{H}) .$ Treating compound $\mathbf{Y}$ with aqueous $\mathrm{NaOH}$ and $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{SO}_{4}$ produces compound $\mathbf{Z}\left(\mathrm{C}_{8} \mathrm{H}_{10} \mathrm{O}_{2}\right) .$ The 'H NMR spectrum of $\mathbf{Z}$ consists of two singlets, one at $\delta 3.75(6 \mathrm{H})$ and one at $\delta 6.8(4 \mathrm{H}) .$ Propose structures for arbutin and for compounds $\mathbf{X}, \mathbf{Y},$ and $\mathbf{Z}$.

Zubair Abdulla

Numerade Educator

Problem 40

When subjected to a Ruff degradation, a D-aldopentose, $A$, is converted to an aldotetrose, B. When reducced with sodium borohydride, the aldotetrose B forms an optically active alditol. The '3C NMR spectrum of this alditol displays only two signals. The alditol obtained by direct reduction of A with sodium borohydride is not optically active. When A is used as the starting material for a KilianiFischer synthesis, two diastereomeric aldohexoses, $\mathbf{C}$ and $\mathbf{D}$, are producced. On treatment with sodium borohydride, C leads to an alditol E, and D leads to F. The '3C NMR spectrum of E consists of three signals; that of $\mathbf{F}$ consists of six. Propose structures for $\mathbf{A}-\mathbf{F}$.

Ronald Prasad

Numerade Educator

Problem 41

Figure 22.21 shows the $^{13} \mathrm{C}$ NMR spectrum for the product of the reaction of D-( $+$ )-mannose with acctone containing a trace of acid. This compound is a mannofuranose with some hydroxyl groups protected as accetone acceals (as acetonides). Use the $^{13} \mathrm{C}$ NMR spectrum to determine how many acetonide groups are present in the compound.

Mikayla Stephens

Mikayla Stephens

Numerade Educator

Problem 42

D-(+)-Mannose can be reduced with sodium borohydride to form D-mannitol. When D-mannitol is dissolved in acetone containing a trace amount of acid and the product of this reaction subsequently oxidized with NalO, a compound whose $^{13} \mathrm{C}$ NMR spectrum consists of six signals is produced. One of these signals is near $\delta$ ) $200 .$ What is the structure of this compound?

Nicole Krahulik

Nicole Krahulik

Numerade Educator

Problem 43

Of the rwo anomers of methyl 2, 3-anhydro-p-ribofuranoside, I, the $\beta$ form has a strikingly lower boiling point. Suggest an explanation using their structural formulas. (FIGURE CAN'T COPY)

Pronoy Sinha

Numerade Educator

Problem 44

The following reaction sequence represents an elegant method of synthesis of 2-deoxy-D-ribose, IV, published by D. C. C. Smith in 1955: (FIGURE CAN'T COPY)

Grigoriy Sereda

Grigoriy Sereda

Numerade Educator

Problem 45

D-Glucose $\frac{\text { acetic anhydride }}{\text { anhydrous }}$ D-Glucopyranose pentaacetate, sodium acetate $$\begin{array}{c}\text { acetic anhydride } \\\text { cat. HA }\end{array} \begin{array}{c}\text { D-Glucopyranose pentaacetate, } \\\text { anomer } \mathbf{V I}\end{array}$$
The 'H NMR data for the two anomers included very comparable peaks in the $\delta 2.0-5.6$ region but differed in that, as their highest $\delta$ peaks, anomer $\mathbf{V}$ had a doublet at $\delta 5.8(1 \mathrm{H}, J=12 \mathrm{Hz})$ while anomer $\mathbf{V I}$ had a doublet at $\delta 6.3(1 \mathrm{H}, J=4 \mathrm{Hz})$
(a) Which proton in these anomers would be expected to have these highest $\delta$ values?
(b) Why do the signals for these protons appear as doublets?
(c) The relationship between the magnitude of the observed coupling constant and the dihedral angle (when measured using a Newman projection) between $\mathrm{C}-\mathrm{H}$ bonds on the adjaccht carbons of a $\mathrm{C}-\mathrm{C}$ bond is given by the Karplus cquation. It indicates that an axialaxial relationship results in a coupling constant of about $9 \mathrm{Hz}$ (observed range is $8-14 \mathrm{Hz}$ ) and an cquatorial-axial relationship results in a coupling constant of about $2 \mathrm{Hz}$ (observed range is $1-7 \mathrm{Hz}$ ). Which of $\mathrm{V}$ and $\mathrm{VI}$ is the $\alpha$ anomer and which is the $\beta$ anomer?
(d) Draw the most stable conformer for each of $\mathbf{V}$ and $\mathbf{V}$.

Anish Wadhwa

Numerade Educator