Organic Chemistry

John McMurry

Chapter 5 Stereochemistry at Tetrahedral Centers - all with Video Answers

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Chapter Questions

03:12

Problem 1

Which of the following objects are chiral?
(b) Screwdriver
(d) Shoe
(a) Soda can
(c) Screw

Bobby Barnes

University of North Texas

05:12

Problem 2

Which of the following molecules are chiral? Identify the chirality center(s) in each.

Bobby Barnes

University of North Texas

02:40

Problem 3

Alanine, an amino acid found in proteins, is chiral. Draw the two enantiomers of alanine using the standard convention of solid, wedged, and dashed lines.

Bobby Barnes

University of North Texas

02:59

Problem 4

Identify the chirality centers in the following molecules (green $=\mathrm{Cl}$, yellow-green $=\mathrm{F}$ ):

Bobby Barnes

University of North Texas

01:12

Problem 5

Is cocaine (Worked Example 5.2 ) dextrorotatory or levorotatory?

Bobby Barnes

University of North Texas

02:51

A $1.50 \mathrm{g}$ sample of coniine, the toxic extract of poison hemlock, was dissolved in $10.0 \mathrm{mL}$ of ethanol and placed in a sample cell with a $5.00 \mathrm{cm}$ pathlength. The observed rotation at the sodium D line was $+1.21^{\circ} .$ Calculate $[\alpha]_{\mathrm{D}}$ for conine.

Bobby Barnes

University of North Texas

04:42

Problem 7

Which member in each of the following sets ranks higher?
(a) $-\mathrm{H}$ or $-\mathrm{Br}$
(b) - Cl or $-B r$
(c) $-\mathrm{CH}_{3}$ or $-\mathrm{CH}_{2} \mathrm{CH}_{3}$
(d) $-\mathrm{NH}_{2}$ or $-\mathrm{OH}$
(e) $-\mathrm{CH}_{2} \mathrm{OH}$ or $-\mathrm{CH}_{3}$
(f) $-\mathrm{CH}_{2} \mathrm{OH}$ or $-\mathrm{CH}=\mathrm{O}$

Bobby Barnes

University of North Texas

09:30

Problem 8

Rank the following sets of substituents:
(a) $-\mathrm{H},-\mathrm{OH},-\mathrm{CH}_{2} \mathrm{CH}_{3},-\mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}$
(b) $-\mathrm{CO}_{2} \mathrm{H},-\mathrm{CO}_{2} \mathrm{CH}_{3},-\mathrm{CH}_{2} \mathrm{OH},-\mathrm{OH}$
(c) $-\mathrm{CN},-\mathrm{CH}_{2} \mathrm{NH}_{2},-\mathrm{CH}_{2} \mathrm{NHCH}_{3},-\mathrm{NH}_{2}$
(d) $-\mathrm{SH},-\mathrm{CH}_{2} \mathrm{SCH}_{3},-\mathrm{CH}_{3},-\mathrm{SSCH}_{3}$

Bobby Barnes

University of North Texas

03:10

Problem 9

Orient each of the following drawings so that the lowest-ranked group is toward the rear, and then assign $R$ or $S$ configuration:

Bobby Barnes

University of North Texas

06:12

Problem 10

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

Bobby Barnes

University of North Texas

02:24

Problem 11

Draw a tetrahedral representation of (S)-2-pentanol (2-hydroxypentane).

Bobby Barnes

University of North Texas

02:38

Problem 12

Assign $R$ or $S$ configuration to the chirality center in the following molecular model of the amino acid methionine (blue $=\mathrm{N},$ yellow $=\mathrm{S}$ ):

Bobby Barnes

University of North Texas

06:16

Problem 13

One of the following molecules (a)-(d) is D-erythrose 4-phosphate, an intermediate in the Calvin photosynthetic cycle by which plants incorporate $\mathrm{CO}_{2}$ into carbohydrates. If D-erythrose 4 -phosphate has $R$ stereochemistry at both chirality centers, which of the structures is it? Which of the remaining three structures is the enantiomer of D-erythrose 4-phosphate, and which are diastereomers?

Bobby Barnes

University of North Texas

03:35

Problem 14

How many chirality centers does morphine have? How many stereoisomers of morphine are possible in principle?

Bobby Barnes

University of North Texas

05:25

Problem 15

Assign $R, S$ configuration to each chirality center in the following molecular model of the amino acid isoleucine (blue $=\mathrm{N}$ ):

Bobby Barnes

University of North Texas

06:54

Problem 16

Which of the following structures represent meso compounds?

Bobby Barnes

University of North Texas

05:32

Problem 17

Which of the following have a meso form? (Recall that the -ol suffix refers to an alcohol, ROH.?
(a) 2,3-Butanediol
(b) 2,3-Pentanediol
(c) 2,4-Pentanediol

Bobby Barnes

University of North Texas

02:27

Problem 18

Does the following structure represent a meso compound? If so, indicate the symmetry plane.

Bobby Barnes

University of North Texas

02:04

Problem 19

Suppose that acetic acid $\left(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}\right)$ reacts with (S)-2-butanol to form an ester (see Worked Example 5.6 ). What stereochemistry would you expect the product(s) to have? What is the relationship of the products?

Bobby Barnes

University of North Texas

06:34

Problem 20

What stereoisomers would result from reaction of ( $_{\pm}$ )-lactic acid with (S)-1-phenylethylamine, and what is the relationship between them?

Bobby Barnes

University of North Texas

03:26

Problem 21

What kinds of isomers are the following pairs?
(a) $(S)-5$ -Chloro-2-hexene and chlorocyclohexane
(b) $(2 R, 3 R)$ -Dibromopentane and $(2 S, 3 R)$ -dibromopentane

Bobby Barnes

University of North Texas

03:26

Problem 22

Identify the indicated hydrogens in the following molecules as pro-R or pro-S:

Bobby Barnes

University of North Texas

01:57

Problem 23

Identify the indicated faces of carbon atoms in the following molecules as Re or Si:

Bobby Barnes

University of North Texas

02:46

Problem 24

The lactic acid that builds up in tired muscles is formed from pyruvate. If the reaction occurs with addition of hydrogen to the Re face of pyruvate, what is the stereochemistry of the product?

Bobby Barnes

University of North Texas

02:47

Problem 25

The aconitase-catalyzed addition of water to cis-aconitate in the citric acid cycle occurs with the following stereochemistry. Does the addition of the OH group occur on the Re or the Si face of the substrate? What about the addition of the H? Do the H and OH groups adds from the same side of the double bond or from opposite sides?

Grigoriy Sereda

Numerade Educator

03:54

Problem 26

Which of the following structures are identical? (Green = Cl.)

Travis Maslanik

Numerade Educator

02:19

Problem 27

Assign $R$ or $S$ configuration to the chirality centers in the following molecules (blue $=\mathrm{N}$ ):

Travis Maslanik

Numerade Educator

03:43

Problem 28

Which, if any, of the following structures represent meso compounds? (Blue $=\mathrm{N},$ green $=$ Cl.)

Travis Maslanik

Numerade Educator

02:29

Problem 29

Assign $R$ or $S$ configuration to each chirality center in pseudoephedrine, an over-the-counter decongestant found in cold remedies (blue = N).

Travis Maslanik

Numerade Educator

02:05

Problem 30

Orient each of the following drawings so that the lowest-ranked group is toward the rear, and then assign $R$ or $S$ configuration:

Grigoriy Sereda

Numerade Educator

02:57

Problem 31

Which of the following objects are chiral?
(a) A basketball
(b) A fork
(c) A wine glass
(d) A golf club
(e) A spiral staircase
(f) A snowflake

Travis Maslanik

Numerade Educator

04:28

Problem 32

Which of the following compounds are chiral? Draw them, and label the chirality centers.
(a) 2,4 -Dimethylheptane
(b) 5 -Ethyl-3,3-dimethylheptane
(c) cis-1,4-Dichlorocyclohexane

Travis Maslanik

Numerade Educator

05:12

Problem 33

A Draw chiral molecules that meet the following descriptions:
(a) A chloroalkane, $\mathrm{C}_{5} \mathrm{H}_{11} \mathrm{Cl}$
(b) An alcohol, $\mathrm{C}_{6} \mathrm{H}_{14} \mathrm{O}$
(c) An alkene, $C_{6} \mathrm{H}_{12}$
(d) An alkane, $\mathrm{C}_{8} \mathrm{H}_{18}$

Travis Maslanik

Numerade Educator

05:04

Problem 34

Eight alcohols have the formula $\mathrm{C}_{5} \mathrm{H}_{12} \mathrm{O}$. Draw them. Which are chiral?

Travis Maslanik

Numerade Educator

05:20

Problem 35

Draw compounds that fit the following descriptions:
(a) A chiral alcohol with four carbons
(b) A chiral carboxylic acid with the formula $\mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O}_{2}$
(c) A compound with two chirality centers
(d) A chiral aldehyde with the formula $\mathrm{C}_{3} \mathrm{H}_{5} \mathrm{BrO}$

Travis Maslanik

Numerade Educator

04:42

Problem 36

Erythronolide $\mathrm{B}$ is the biological precursor of erythromycin, a broad-spectrum antibiotic. How many chirality centers does erythronolide B have? Identify them.

Travis Maslanik

Numerade Educator

06:39

Problem 37

Which of the following pairs of structures represent the same enantiomer, and which represent different enantiomers?

Travis Maslanik

Numerade Educator

03:52

Problem 38

What is the relationship between the specific rotations of (2R,3R)-dichloropentane and (25,3S)-dichloropentane? Between (2R,3S)-dichloropentane and $(2 R, 3 R)$ -dichloropentane?

Travis Maslanik

Numerade Educator

04:19

Problem 39

What is the stereochemical configuration of the enantiomer of $(2 S, 4 R)$ 2,4-octanediol? (A diol is a compound with two -OH groups.)

Travis Maslanik

Numerade Educator

05:41

Problem 40

What are the stereochemical configurations of the two diastereomers of $(2 S, 4 R)-2,4$ -octanediol? (A diol is a compound with two - OH groups.)

Travis Maslanik

Numerade Educator

03:42

Problem 41

Orient each of the following drawings so that the lowest-ranked group is toward the rear, and then assign $R$ or $S$ configuration:

Ronald Prasad

Numerade Educator

04:17

Problem 42

Assign Cahn-Ingold-Prelog rankings to the following sets of substituents:
(a) $-\mathrm{CH}=\mathrm{CH}_{2},-\mathrm{CH}\left(\mathrm{CH}_{3}\right)_{2},-\mathrm{C}\left(\mathrm{CH}_{3}\right)_{3},-\mathrm{CH}_{2} \mathrm{CH}_{3}$
(b) $-\mathrm{C} \equiv \mathrm{CH},-\mathrm{CH}=\mathrm{CH}_{2},-\mathrm{C}\left(\mathrm{CH}_{3}\right)_{3}$
(c) $-\mathrm{CO}_{2} \mathrm{CH}_{3},-\mathrm{COCH}_{3},-\mathrm{CH}_{2} \mathrm{OCH}_{3},-\mathrm{CH}_{2} \mathrm{CH}_{3}$
(d) $-\mathrm{C} \equiv \mathrm{N},-\mathrm{CH}_{2} \mathrm{Br},-\mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Br},-\mathrm{Br}$

Ronald Prasad

Numerade Educator

02:36

Problem 43

Assign $R$ or $S$ configurations to the chirality centers in the following molecules:

Travis Maslanik

Numerade Educator

05:25

Problem 44

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

Travis Maslanik

Numerade Educator

03:30

Problem 45

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

Grigoriy Sereda

Numerade Educator

04:38

Problem 46

Draw tetrahedral representations of the following molecules:
(a) $(S)-2-$ Chlorobutane
(b) $(R)-3$ -Chloro-1-pentene $\left[\mathrm{H}_{2} \mathrm{C}=\mathrm{CHCH}(\mathrm{Cl}) \mathrm{CH}_{2} \mathrm{CH}_{3}\right]$

Travis Maslanik

Numerade Educator

04:09

Problem 47

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

Travis Maslanik

Numerade Educator

03:58

Problem 48

Assign $R$ or $S$ configurations to the chirality centers in ascorbic acid (vitamin C).

Travis Maslanik

Numerade Educator

06:40

Problem 49

Assign $R$ or $S$ stereochemistry to the chirality centers in the following Newman projections:

Travis Maslanik

Numerade Educator

04:43

Problem 50

Xylose is a common sugar found in many types of wood, including maple and cherry. Because it is much less prone to cause tooth decay than sucrose, xylose has been used in candy and chewing gum. Assign $R$ or $S$ configurations to the chirality centers in xylose.

Travis Maslanik

Numerade Educator

05:38

Problem 51

Draw examples of the following:
(a) A meso compound with the formula $\mathrm{C}_{8} \mathrm{H}_{18}$
(b) A meso compound with the formula $\mathrm{C}_{9} \mathrm{H}_{20}$
(c) A compound with two chirality centers, one $R$ and the other $S$

Travis Maslanik

Numerade Educator

01:12

Problem 52

Draw the meso form of each of the following molecules, and indicate the plane of symmetry in each:

David Collins

Numerade Educator

01:22

Problem 53

Draw the structure of a meso compound that has five carbons and three chirality centers.

David Collins

Numerade Educator

04:20

Problem 54

(a) How many chirality centers does ribose have? Identify them.
(b) How many stereoisomers of ribose are there?
(c) Draw the structure of the enantiomer of ribose.
(d) Draw the structure of a diastereomer of ribose.

Ronald Prasad

Numerade Educator

00:55

Problem 55

On reaction with hydrogen gas with a platinum catalyst, ribose (Problem 5.54) is converted into ribitol. Is ribitol optically active or inactive? Explain.

Grigoriy Sereda

Numerade Educator

03:00

Problem 56

Identify the indicated hydrogens in the following molecules as pro-R or pro-S:

Ronald Prasad

Numerade Educator

04:04

Problem 57

Identify the indicated faces in the following molecules as Re or Si:

Ronald Prasad

Numerade Educator

02:22

Problem 58

One of the steps in fat metabolism is the hydration of crotonate to yield 3-hydroxybutyrate. The reaction occurs by addition of $-\mathrm{OH}$ to the $S i$ face at C3, followed by protonation at $\mathrm{C} 2,$ also from the $S i$ face. Draw the product of the reaction, showing the stereochemistry of each step.

Grigoriy Sereda

Numerade Educator

01:34

Problem 59

The dehydration of citrate to yield cis-aconitate, a step in the citric acid cycle, involves the pro-R "arm" of citrate rather than the pro-S arm. Which of the following two products is formed?

Grigoriy Sereda

Numerade Educator

01:45

Problem 60

The first step in the metabolism of glycerol, formed by digestion of fats, is phosphorylation of the $p r o-R-\mathrm{CH}_{2} \mathrm{OH}$ group by reaction with adenosine triphosphate (ATP) to give the corresponding glycerol phosphate plus adenosine diphosphate (ADP). Show the stereochemistry of the product.

Grigoriy Sereda

Numerade Educator

02:46

Problem 61

One of the steps in fatty-acid biosynthesis is the dehydration of (R)-3-hydroxybutyryl ACP to give trans-crotonyl ACP. Does the reaction remove the pro-R or the pro-S hydrogen from C2?

Lottie Adams

Numerade Educator

10:46

Problem 62

Draw all possible stereoisomers of 1,2-cyclobutanedicarboxylic acid, and indicate the interrelationships. Which, if any, are optically active? Do the same for 1,3-cyclobutanedicarboxylic acid.

Bobby Barnes

University of North Texas

01:31

Problem 63

Draw tetrahedral representations of the two enantiomers of the amino acid cysteine, $\mathrm{HSCH}_{2} \mathrm{CH}\left(\mathrm{NH}_{2}\right) \mathrm{CO}_{2} \mathrm{H},$ and identify each as $R$ or $S.$

Grigoriy Sereda

Numerade Educator

00:46

Problem 64

The naturally occurring form of the amino acid cysteine (Problem 5.63) has the $S$ configuration at its chirality center. On treatment with a mild oxidizing agent, two cysteines join to give cystine, a disulfide. Assuming that the chirality center is not affected by the reaction, is cystine optically active? Explain.

Grigoriy Sereda

Numerade Educator

03:17

Problem 65

Draw tetrahedral representations of the following molecules:
(a) The $2 S, 3 R$ enantiomer of 2,3-dibromopentane
(b) The meso form of 3,5-heptanediol

Ronald Prasad

Numerade Educator

01:39

Problem 66

Assign $R, S$ configurations to the chiral centers in cephalexin, trade-named Keflex, the most widely prescribed antibiotic in the United States.

Grigoriy Sereda

Numerade Educator

00:53

Problem 67

Chloramphenicol, a powerful antibiotic isolated in 1949 from the Streptomyces venezuelae bacterium, is active against a broad spectrum of bacterial infections and is particularly valuable against typhoid fever. Assign $R, S$ configurations to the chirality centers in chloramphenicol.

Grigoriy Sereda

Numerade Educator

01:40

Problem 68

Allenes are compounds with adjacent carbon-carbon double bonds. Many allenes are chiral, even though they don't contain chirality centers. Mycomycin, for example, a naturally occurring antibiotic isolated from the bacterium Nocardia acidophilus, is chiral and has $[\alpha]_{\mathrm{D}}=-130 .$ Explain why mycomycin is chiral.
$$\mathrm{HC} \equiv \mathrm{C}-\mathrm{C} \equiv \mathrm{C}-\mathrm{CH}=\mathrm{C}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{H}$$

Grigoriy Sereda

Numerade Educator

01:25

Problem 69

Long before chiral allenes were known (Problem 5.68 ), the resolution of 4-methylcyclohexylideneacetic acid into two enantiomers had been carried out. Why is it chiral? What geometric similarity does it have to allenes?

Grigoriy Sereda

Numerade Educator

01:47

Problem 70

(S)-1-Chloro-2-methylbutane undergoes light-induced reaction with Cla to yield a mixture of products, among which are 1,4 -dichloro- 2 -methylbutane and 1,2 -dichloro- 2 -methylbutane.
(a) Write the reaction, showing the correct stereochemistry of the reactant.
(b) One of the two products is optically active, but the other is optically inactive. Which is which?

Grigoriy Sereda

Numerade Educator

02:36

Problem 71

How many stereoisomers of 2,4 -dibromo-3-chloropentane are there? Draw them, and indicate which are optically active.

Nicole Krahulik

Numerade Educator

02:36

Problem 72

Draw both cis- and trans-1,4-dimethylcyclohexane in their more stable chair conformations.
(a) How many stereoisomers are there of $c i s-1,4$ -dimethylcyclohexane, and how many of trans-1,4-dimethylcyclohexane?
(b) Are any of the structures chiral?
(c) What are the stereochemical relationships among the various stereoisomers of 1,4 -dimethylcyclohexane?

Grigoriy Sereda

Numerade Educator

11:10

Problem 73

Draw both cis- and trans-1,3-dimethylcyclohexane in their more stable chair conformations.
(a) How many stereoisomers are there of cis-1,3-dimethylcyclohexane, and how many of trans-1,3-dimethylcyclohexane?
(b) Are any of the structures chiral?
(c) What are the stereochemical relationships among the various stereoisomers of 1,3 -dimethylcyclohexane?

Ronald Prasad

Numerade Educator

01:32

Problem 74

cis-1,2-Dimethylcyclohexane is optically inactive even though it has two chirality centers. Explain.

Grigoriy Sereda

Numerade Educator

01:23

Problem 75

We'll see in Chapter 11 that alkyl halides react with hydrosulfide ion (HS $^{-}$ ) to give a product whose stereochemistry is inverted from that of the reactant.
Draw the reaction of ( $S$ )-2-bromobutane with HS - ion to yield 2-butanethiol, $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}(\mathrm{SH}) \mathrm{CH}_{3} .$ Is the stereochemistry of the product $R$ or $S ?$

Grigoriy Sereda

Numerade Educator

02:22

Problem 76

Ketones react with sodium acetylide (the sodium salt of acetylene, $\left.\mathrm{Na}^{+-}: \mathrm{C} \equiv \mathrm{CH}\right)$ to give alcohols. For example, the reaction of sodium acetylide with 2-butanone yields 3-methyl-1-pentyn-3-ol:
(a) Is the product chiral?
(b) Assuming that the reaction takes place with equal likelihood from both Re and Si faces of the carbonyl group, is the product optically active? Explain.

Grigoriy Sereda

Numerade Educator

02:46

Problem 77

Imagine that a reaction similar to that in Problem 5.76 is carried out between sodium acetylide and ( $R$ )-2-phenylpropanal to yield 4-phenyl-1-pentyn-3-ol:
(a) Is the product chiral?
(b) Draw both major and minor reaction products, assuming that the reaction takes place preferentially from the Re face of the carbonyl group. Is the product mixture optically active? Explain.

Grigoriy Sereda

Numerade Educator