Organic Chemistry

John McMurry

Chapter 25 Biomolecules: Carbohydrates - all with Video Answers

Educators

Chapter Questions

02:36

Problem 1

Classify each of the following monosaccharides:
a) Threose
b) Ribulose
c) Tagatose
d) 2-Deoxyribose

Ricajoy Montero

Numerade Educator

06:08

Problem 2

Convert each of the following Fischer projections into a tetrahedral representation, and assign $R$ or $S$ stereochemistry:

Ricajoy Montero

Numerade Educator

03:12

Problem 3

Which of the following Fischer projections of glyceraldehyde represent the same enantiomer?

Mikayla Stephens

Numerade Educator

04:57

Problem 4

Redraw the following molecule as a Fischer projection, and assign $R$ or $S$ configuration to the chirality center (green $=\mathrm{Cl})$ :

Ricajoy Montero

Numerade Educator

06:21

Problem 5

Redraw the following aldotetrose as a Fischer projection, and assign $R$ or $S$ configuration to each chirality center:

Ricajoy Montero

Numerade Educator

06:43

Problem 6

Assign $R$ or $S$ configuration to each chirality center in the following monosaccharides, and tell whether each is a D sugar or an L sugar:

Ricajoy Montero

Numerade Educator

03:44

$(+)-$Arabinose, an aldopentose that is widely distributed in plants, is systematically named $(2 R, 3 S, 4 S)-2,3,4,5$ -tetrahydroxypentanal. Draw a Fischer projection of $(+)$ -arabinose, and identify it as a D sugar or an L sugar.

Ricajoy Montero

Numerade Educator

04:23

Problem 8

Only the D sugars are shown in Figure 25.3. Draw Fischer projections for the following L sugars:
(a) L-Xylose
(b) L-Galactose
(c) L-Allose

Ricajoy Montero

Numerade Educator

01:40

Problem 9

How many aldoheptoses are there? How many are D sugars, and how many are L sugars?

Ricajoy Montero

Numerade Educator

06:00

Problem 10

The following model is that of an aldopentose. Draw a Fischer projection of the sugar, name it, and identify it as a D sugar or an L sugar.

Ricajoy Montero

Numerade Educator

02:44

Problem 11

Ribose exists largely in a furanose form, produced by addition of the C4-OH group to the C1 aldehyde. Draw D-ribose in its furanose form.

Ricajoy Montero

Numerade Educator

04:34

Problem 12

Figure 25.5 shows only the $\beta$-pyranose and $\beta$-furanose anomers of $\mathrm{D}$-fructose. Draw the $\alpha$-pyranose and $\alpha$-furanose anomers.

Ricajoy Montero

Numerade Educator

01:54

Problem 13

Draw $\beta$-D-galactopyranose and $\beta$-D-mannopyranose in their more stable chair conformations. Label each ring substituent as either axial or equatorial. Which would you expect to be more stable, galactose or mannose?

Mikayla Stephens

Numerade Educator

04:53

Problem 14

Draw $\beta$-L-galactopyranose in its more stable chair conformation, and label the substituents as either axial or equatorial.

Ricajoy Montero

Numerade Educator

04:56

Problem 15

Identify the following monosaccharide, write its full name, and draw its open-chain form in Fischer projection.

Ricajoy Montero

Numerade Educator

03:37

Problem 16

Draw the products you would obtain by reaction of $\beta$ - $\mathrm{D}$ -ribofuranose with:
(a) $\mathrm{CH}_{3} \mathrm{I}, \mathrm{Ag}_{2} \mathrm{O}$
(b) $\left(\mathrm{CH}_{3} \mathrm{CO}\right)_{2} \mathrm{O},$ pyridine

Ricajoy Montero

Numerade Educator

03:14

Problem 17

Reduction of D-glucose leads to an optically active alditol (D-glucitol), whereas reduction of D-galactose leads to an optically inactive alditol. Explain.

Ricajoy Montero

Numerade Educator

02:33

Problem 18

Reduction of L-gulose with $\mathrm{NaBH}_{4}$ leads to the same alditol (D-glucitol) as reduction of D-glucose. Explain.

Ricajoy Montero

Numerade Educator

02:15

Problem 19

D-Glucose yields an optically active aldaric acid on treatment with $\mathrm{HNO}_{3}$, but D-allose yields an optically inactive aldaric acid. Explain.

Ricajoy Montero

Numerade Educator

05:11

Problem 20

Which of the other six $\mathrm{D}$ aldohexoses yield optically active aldaric acids on oxidation, and which yield optically inactive (meso) aldaric acids? (See Problem 25.19.)

Ricajoy Montero

Numerade Educator

03:26

Problem 21

What product(s) would you expect from Kiliani-Fischer reaction of D-ribose?

Ricajoy Montero

Numerade Educator

03:05

Problem 22

What aldopentose would give a mixture of L-gulose and L-idose on Kiliani-Fischer chain extension?

Ricajoy Montero

Numerade Educator

01:58

Problem 23

Two of the four $\mathrm{D}$ aldopentoses yield $\mathrm{D}$ -threose on Wohl degradation. What are their structures?

Ricajoy Montero

Numerade Educator

02:19

Problem 24

Show how neuraminic acid can arise by an aldol reaction of $N$ -acetylmannosamine with pyruvate $\left(\mathrm{CH}_{3} \mathrm{COCO}_{2}^{-}\right)$.

Ricajoy Montero

Numerade Educator

02:17

Problem 25

Show the product you would obtain from the reaction of cellobiose with the following reagents:
(a) $\mathrm{NaBH}_{4}$
(b) $\mathrm{Br}_{2}, \mathrm{H}_{2} \mathrm{O}$
(c) $\mathrm{CH}_{3} \mathrm{COCl},$ pyridine

Anand Jangid

Numerade Educator

02:27

Problem 26

Identify the following aldoses, and tell whether each is a D or L sugar:

Mikayla Stephens

Numerade Educator

03:03

Problem 27

Draw Fischer projections of the following molecules, placing the carbonyl group at the top in the usual way. Identify each as a D or L sugar.

Ricajoy Montero

Numerade Educator

00:57

Problem 28

The following structure is that of an L aldohexose in its pyranose form. Identify it, and tell whether it is an $\alpha$ or $\beta$ anomer.

Ricajoy Montero

Numerade Educator

04:06

Problem 29

The following model is that of an aldohexose:
(a) Draw Fischer projections of the sugar, its enantiomer, and a diastereomer.
(b) Is this a n sugar or an L sugar? Explain.
(c) Draw the $\beta$ anomer of the sugar in its furanose form.

Mikayla Stephens

Numerade Educator

02:19

Problem 30

Classify each of the following sugars. (For example, glucose is an aldohexose.)
(a) $\mathrm{CH}_{2} \mathrm{OH}$
(b) $\mathrm{CH}_{2} \mathrm{OH}$
(c) CHO

Ricajoy Montero

Numerade Educator

05:53

Problem 31

Write open-chain structures for the following:
(a) A ketotetrose
(b) A ketopentose
(c) A deoxyaldohexose
(d) A five-carbon amino sugar

Ricajoy Montero

Numerade Educator

01:58

Problem 32

What is the stereochemical relationship of D-ribose to L-xylose? What generalizations can you make about the following properties of the two sugars?
(a) Melting point
(b) Solubility in water
(c) Specific rotation
(d) Density

Ricajoy Montero

Numerade Educator

02:01

Problem 33

Does ascorbic acid (vitamin $\mathrm{C}$ ) have a D or L configuration?

Ricajoy Montero

Numerade Educator

04:32

Problem 34

Draw the three-dimensional furanose form of ascorbic acid (Problem 25.33 ), and assign $R$ or $S$ stereochemistry to each chirality center.

Ricajoy Montero

Numerade Educator

02:06

Problem 35

Assign $R$ or $S$ configuration to each chirality center in the following molecules:

Mikayla Stephens

Numerade Educator

04:53

Problem 36

Draw Fischer projections of the following molecules:
(a) The $S$ enantiomer of 2-bromobutane
(b) The $R$ enantiomer of alanine, $\mathrm{CH}_{3} \mathrm{CH}\left(\mathrm{NH}_{2}\right) \mathrm{CO}_{2} \mathrm{H}$
(c) The $R$ enantiomer of 2-hydroxypropanoic acid
(d) The $S$ enantiomer of 3-methylhexane

Ricajoy Montero

Numerade Educator

02:28

Problem 37

Draw Fischer projections for the two $\mathrm{D}$ aldoheptoses whose stereochemistry at $\mathrm{C} 3, \mathrm{C} 4, \mathrm{C} 5,$ and $\mathrm{C} 6$ is the same as that of D-glucose at $\mathrm{C} 2, \mathrm{C} 3, \mathrm{C} 4,$ and $\mathrm{C} 5.$

Ricajoy Montero

Numerade Educator

02:14

Problem 38

The following cyclic structure is that of allose. Is this a furanose or pyranose form? Is it an $\alpha$ or $\beta$ anomer? Is it a D or L sugar?

Ricajoy Montero

Numerade Educator

00:40

Problem 39

What is the complete name of the following sugar?

Mikayla Stephens

Numerade Educator

01:23

Problem 40

Write the following sugars in their open-chain forms:

Mikayla Stephens

Numerade Educator

02:37

Problem 41

Draw D-ribulose in its five-membered cyclic $\beta$ -hemiacetal form.

Ricajoy Montero

Numerade Educator

04:07

Problem 42

Look up the structure of D-talose in Figure $25.3,$ and draw the $\beta$ anomer in its pyranose form. Identify the ring substituents as axial or equatorial.

Ricajoy Montero

Numerade Educator

03:28

Problem 43

Draw structures for the products you would expect to obtain from reaction of $\beta$ -D-talopyranose with each of the following reagents:
(a) $\mathrm{NaBH}_{4}$ in $\mathrm{H}_{2} \mathrm{O}$
(b) Warm dilute HNO $_{3}$
(c) $\mathrm{Br}_{2}, \mathrm{H}_{2} \mathrm{O}$
(d) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}, \mathrm{HCl}$
(e) $\mathrm{CH}_{3} \mathrm{I}, \mathrm{Ag}_{2} \mathrm{O}$
(f) $\left(\mathrm{CH}_{3} \mathrm{CO}\right)_{2} \mathrm{O},$ pyridine

Mikayla Stephens

Numerade Educator

04:24

Problem 44

How many D-2-ketohexoses are possible? Draw them.

Ricajoy Montero

Numerade Educator

01:45

Problem 45

One of the D-2-ketohexoses is called sorbose. On treatment with $\mathrm{NaBH}_{4},$ sorbose yields a mixture of gulitol and iditol. What is the structure of sorbose?

Ricajoy Montero

Numerade Educator

01:53

Problem 46

Another D-2-ketohexose, psicose , yields a mixture of allitol and altritol when reduced with $\mathrm{NaBH}_{4} .$ What is the structure of psicose?

Ricajoy Montero

Numerade Educator

01:24

Problem 47

L-Gulose can be prepared from D-glucose by a route that begins with oxidation to D-glucaric acid, which cyclizes to form two six-membered-ring lactones. Separating the lactones and reducing them with sodium amalgam gives D-glucose and L-gulose. What are the structures of the two lactones, and which one is reduced to L-gulose?

Mikayla Stephens

Numerade Educator

01:27

Problem 48

Gentiobiose, a rare disaccharide found in saffron and gentian, is a reducing sugar and forms only D-glucose on hydrolysis with aqueous acid. Reaction of gentiobiose with iodomethane and $\mathrm{Ag}_{2} \mathrm{O}$ yields an octamethyl derivative, which can be hydrolyzed with aqueous acid to give 1 equivalent of 2,3,4,6-tetraO-methyl-D-glucopyranose and 1 equivalent of 2,3,4-tri-O-methyl-p-glucopyranose. If gentiobiose contains a $\beta$-glycoside link, what is its structure?

Mikayla Stephens

Numerade Educator

02:19

Problem 49

All aldoses exhibit mutarotation. For example, $\alpha$ -D-galactopyranose has $[\alpha]_{\mathrm{D}}=+150.7,$ and $\beta$ -D-galactopyranose has $[\alpha]_{\mathrm{D}}=+52.8 .$ If either anomer is dissolved in water and allowed to reach equilibrium, the specific rotation of the solution is $+80.2 .$ What are the percentages of each anomer at equilibrium? Draw the pyranose forms of both anomers.

Mikayla Stephens

Numerade Educator

03:44

Problem 50

What other $\mathrm{D}$ aldohexose gives the same alditol as $\mathrm{D}$ -talose?

Ricajoy Montero

Numerade Educator

06:56

Problem 51

Which of the eight $\mathrm{D}$ aldohexoses give the same aldaric acids as their L enantiomers?

Ricajoy Montero

Numerade Educator

03:27

Problem 52

Which of the other three $\mathrm{D}$ aldopentoses gives the same aldaric acid as D-lyxose?

Ricajoy Montero

Numerade Educator

01:35

Problem 53

Draw the structure of L-galactose, and then answer the following questions:
(a) Which other aldohexose gives the same aldaric acid as L-galactose on oxidation with warm HNO $_{3} ?$
(b) Is this other aldohexose a D sugar or an L sugar?
(c) Draw this other aldohexose in its most stable pyranose conformation.

Mikayla Stephens

Numerade Educator

02:04

Problem 54

Galactose, one of the eight essential monosaccharides (Section $25.7),$ is biosynthesized from UDP glucose by galactose 4 -epimerase, where UDP $=$ uridylyl diphosphate (a ribonucleotide diphosphate; Section 28.1). The enzyme requires $\left.\mathrm{NAD}^{+} \text {for activity (Section } 17.7\right),$ but it is not a stoichiometric reactant, and NADH is not a final reaction product. Propose a mechanism.

Mikayla Stephens

Numerade Educator

03:45

Problem 55

Mannose, one of the eight essential monosaccharides (Section $25.7),$ is biosynthesized as its 6-phosphate derivative from fructose 6-phosphate. No enzyme cofactor is required. Propose a mechanism.

Mikayla Stephens

Numerade Educator

03:42

Problem 56

Glucosamine, one of the eight essential monosaccharides (Section 25.7 ), is biosynthesized as its 6-phosphate derivative from fructose 6-phosphate by reaction with ammonia. Propose a mechanism.

Mikayla Stephens

Numerade Educator

04:02

Problem 57

Amygdalin, or laetrile, is a cyanogenic glycoside isolated in 1830 from almond and apricot seeds. Acidic hydrolysis of amygdalin liberates HCN, along with benzaldehyde and 2 equivalents of n-glucose. If amygdalin is a $\beta$-glycoside of benzaldehyde cyanohydrin with gentiobiose (Problem $21.56)$ what is its structure?

Ricajoy Montero

Numerade Educator

00:52

Problem 58

Trehalose is a nonreducing disaccharide that is hydrolyzed by aqueous acid to yield 2 equivalents of D-glucose. Methylation followed by hydrolysis yields 2 equivalents of $2,3,4,6-$ tetra-O-methylglucose. How many structures are possible for trehalose?

Mikayla Stephens

Numerade Educator

01:17

Problem 59

Trehalose (Problem 25.58 ) is cleaved by enzymes that hydrolyze $\alpha$-glycosides but not by enzymes that hydrolyze $\beta$-glycosides. What is the structure and systematic name of trehalose?

Mikayla Stephens

Numerade Educator

01:50

Problem 60

Isotrehalose and neotrehalose are chemically similar to trehalose (Problems 25.58 and 25.59 ) except that neotrehalose is hydrolyzed only by $\beta$-glycosidase enzymes, whereas isotrehalose is hydrolyzed by both $\alpha$- and $\beta$-glycosidase enzymes. What are the structures of isotrehalose and neotrehalose?

Mikayla Stephens

Numerade Educator

02:18

Problem 61

D-Glucose reacts with acetone in the presence of acid to yield the nonreducing 1,$2: 5,6-$ diisopropylidene-D-glucofuranose. Propose a mechanism.

Mikayla Stephens

Numerade Educator

02:55

Problem 62

D-Mannose reacts with acetone to give a diisopropylidene derivative (Problem 25.61 ) that is still reducing toward Tollens' reagent. Propose a likely structure for this derivative.

Ricajoy Montero

Numerade Educator

02:45

Problem 63

Glucose and mannose can be interconverted (in low yield) by treatment with dilute aqueous NaOH. Propose a mechanism.

Mikayla Stephens

Numerade Educator

03:25

Problem 64

Propose a mechanism to account for the fact that D-gluconic acid and D-mannonic acid are interconverted when either is heated in pyridine solvent.

Mikayla Stephens

Numerade Educator

02:27

Problem 65

The cyclitols are a group of carbocyclic sugar derivatives having the general formulation 1,2,3,4,5,6-cyclohexanehexol. How many stereoisomeric cyclitols are possible? Draw them in their chair forms.

Mikayla Stephens

Numerade Educator

03:51

Problem 66

Compound $A$ is a $D$ aldopentose that can be oxidized to an optically inactive aldaric acid B. On Kiliani-Fischer chain extension, A is converted into C and $\mathbf{D} ; \mathbf{C}$ can be oxidized to an optically active aldaric acid $\mathbf{E},$ but $\mathbf{D}$ is oxidized to an optically inactive aldaric acid F. What are the structures of A-F?

Mikayla Stephens

Numerade Educator

03:53

Problem 67

Simple sugars undergo reaction with phenylhydrazine, PhNHNH_, to yield crystalline derivatives called osazones. The reaction is a bit complex, however, as shown by the fact that glucose and fructose yield the same osazone.
(a) Draw the structure of a third sugar that yields the same osazone as glucose and fructose.
(b) Using glucose as the example, the first step in osazone formation is reaction of the sugar with phenylhydrazine to yield an imine called a phenylhydrazone. Draw the structure of the product.
(c) The second and third steps in osazone formation are tautomerization of the phenylhydrazone to give an enol, followed by elimination of aniline to give a keto imine. Draw the structures of both the enol tautomer and the keto imine.
(d) The final step is reaction of the keto imine with 2 equivalents of phenylhydrazine to yield the osazone plus ammonia. Propose a mechanism for this step.

Mikayla Stephens

Numerade Educator

04:06

Problem 68

(a) Draw D-idose in its pyranose form, showing the more stable chair conformation of the ring.
(b) Which is more stable, $\alpha$-D-idopyranose or $\beta$ -D-idopyranose? Explain.
(c) Draw 1,6 -anhydro-D-idopyranose in its most stable conformation.
(d) When heated to $100^{\circ} \mathrm{C}$ under the same conditions as those used for D-idose, D-glucose does not lose water and does not exist in a 1,6 -anhydro form. Explain.

Mikayla Stephens

Numerade Educator

02:16

Problem 69

Acetyl coenzyme $A$ (acetyl CoA) is the key intermediate in food metabolism. What sugar is present in acetyl CoA?

Ricajoy Montero

Numerade Educator

02:03

Problem 70

One of the steps in the biological pathway for carbohydrate metabolism is the conversion of fructose 1,6-bisphosphate into dihydroxyacetone phosphate and glyceraldehyde 3-phosphate. Propose a mechanism for the transformation.

Mikayla Stephens

Numerade Educator

08:13

Problem 71

L-Fucose, one of the eight essential monosaccharides (Section 25.7 ), is biosynthesized from GDP-D-mannose by the following three-step reaction sequence, where GDP$=$ guanosine diphosphate (a ribonucleoside diphosphate; Section28.1):
(a) Step 1 involves an oxidation to a ketone, a dehydration to an enone, and a conjugate reduction. The step requires $\mathrm{NADP}^{+},$ but no NADPH is formed as a final reaction product. Propose a mechanism.
(b) Step 2 accomplishes two epimerizations and utilizes acidic and basic sites in the enzyme but does not require a coenzyme. Propose a mechanism.
(c) Step 3 requires NADPH as coenzyme. Show the mechanism.

Mikayla Stephens

Numerade Educator