5.17: Additional Problems
- Page ID
- 459866
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Visualizing Chemistry
Which of the following structures are identical? (Green = Cl.)
(a) (b) (c)
(d)
R or S configurations to the chirality centers in the following molecules (blue = N):
(a)
(b)
(b)
(c)
Problem 5-29
Assign R or S configuration to each chirality center in pseudoephedrine, an over-the-counter decongestant found in cold remedies (blue = N).
R or S configuration:
(a)
(b)
(c)
Chirality and Optical Activity
Problem 5-31
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
2,4-Dimethylheptane
(b)
5-Ethyl-3,3-dimethylheptane
(b)
(c)
Problem 5-29
Assign R or S configuration to each chirality center in pseudoephedrine, an over-the-counter decongestant found in cold remedies (blue = N).
R or S configuration:
(a)
(b)
(c)
Chirality and Optical Activity
Problem 5-31
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
2,4-Dimethylheptane
A chloroalkane, C5H11Cl
Eight alcohols have the formula C5H12O. Draw them. Which are chiral?
A chiral alcohol with four carbons
Erythronolide B is the biological precursor of erythromycin, a broad-spectrum antibiotic. How many chirality centers does erythronolide B have? Identify them.
Assigning Configuration to Chirality Centers
(b)
(c)
(d)
What is the relationship between the specific rotations of (2R,3R)-dichloropentane and (2S,3S)-dichloropentane? Between (2R,3S)-dichloropentane and (2R,3R)-dichloropentane?
What is the stereochemical configuration of the enantiomer of (2S,4R)-2,4-octanediol?
What are the stereochemical configurations of the two diastereomers of (2S,4R)-2,4-octanediol? (A diol is a compound with two – OH groups.)
R or S configuration:
(a)
(b)
(c)
Problem 5-42
Assign Cahn–Ingold–Prelog rankings to the following sets of substituents:
(a)
(b)
(c)
(d)
Problem 5-43
Assign R or S configurations to each chirality center in the following molecules:
(a)
(b)
(c)
Problem 5-44
Assign R or S configuration to each chirality center in the following molecules:
(a)
(b)
(c)
Problem 5-45
Assign R or S configuration to each chirality center in the following biological molecules:
(a)
(b)
Problem 5-46
Draw tetrahedral representations of the following molecules:
(a)
(S)-2-Chlorobutane
What is the relationship between the specific rotations of (2R,3R)-dichloropentane and (2S,3S)-dichloropentane? Between (2R,3S)-dichloropentane and (2R,3R)-dichloropentane?
What is the stereochemical configuration of the enantiomer of (2S,4R)-2,4-octanediol?
What are the stereochemical configurations of the two diastereomers of (2S,4R)-2,4-octanediol? (A diol is a compound with two – OH groups.)
R or S configuration:
(a)
(b)
(c)
Problem 5-42
Assign Cahn–Ingold–Prelog rankings to the following sets of substituents:
(a)
(b)
(c)
(d)
Problem 5-43
Assign R or S configurations to each chirality center in the following molecules:
(a)
(b)
(c)
Problem 5-44
Assign R or S configuration to each chirality center in the following molecules:
(a)
(b)
(c)
Problem 5-45
Assign R or S configuration to each chirality center in the following biological molecules:
(a)
(b)
Problem 5-46
Draw tetrahedral representations of the following molecules:
(a)
(S)-2-ChlorobutaneR or S configuration to each chirality center in the following molecules:
(a)
(b)
Assign R or S configurations to the chirality centers in ascorbic acid (vitamin C).
Assign R or S configurations to the chirality centers in ascorbic acid (vitamin C).
R or S stereochemistry to the chirality centers in the following Newman projections:
(a)
(b)
Problem 5-50
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.
Meso Compounds
A meso compound with the formula C8H18
(b)
(c)
Draw the structure of a meso compound that has five carbons and three chirality centers.
Ribose, an essential part of ribonucleic acid (RNA), has the following structure:
(a)
How many chirality centers does ribose have? Identify them.
Draw the structure of a meso compound that has five carbons and three chirality centers.
Ribose, an essential part of ribonucleic acid (RNA), has the following structure: (a)
How many chirality centers does ribose have? Identify them.On reaction with hydrogen gas in the presence of a platinum catalyst, ribose (Problem 5-54) is converted into ribitol. Is ribitol optically active or inactive? Explain.
Prochirality
R or pro-S:
(a)
(b)
(c)
(b)
Problem 5-58
One of the steps in fat metabolism is the hydration of crotonate to yield 3-hydroxybutyrate. The reaction occurs by addition of – OH to the Si face at C3, followed by protonation at C2, also from the Si face. Draw the product of the reaction, showing the stereochemistry of each step.
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?
(b)
Problem 5-58
One of the steps in fat metabolism is the hydration of crotonate to yield 3-hydroxybutyrate. The reaction occurs by addition of – OH to the Si face at C3, followed by protonation at C2, also from the Si face. Draw the product of the reaction, showing the stereochemistry of each step.
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?
The first step in the metabolism of glycerol, formed by digestion of fats, is phosphorylation of the pro-R – CH2OH group by reaction with adenosine triphosphate (ATP) to give the corresponding glycerol phosphate plus adenosine diphosphate (ADP). Show the stereochemistry of the product.
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?
General Problems
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.
Draw tetrahedral representations of the two enantiomers of the amino acid cysteine, HSCH2CH(NH2)CO2H, and identify each as R or S.
The naturally occurring form of the amino acid cysteine (Problem 5-63) has the R 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.
The 2S,3R enantiomer of 2,3-dibromopentane
Assign R or S configurations to the chiral centers in cephalexin, trade-named Keflex, the most widely prescribed antibiotic in the United States.
Chloramphenicol, a powerful antibiotic isolated in 1947 from the Streptomyces venezuelae bacterium, is active against a broad spectrum of bacterial infections and is particularly valuable against typhoid fever. Assign R or S configurations to the chirality centers in chloramphenicol.
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 [α]D = −130. Explain why mycomycin is chiral.
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?
S)-1-Chloro-2-methylbutane undergoes light-induced reaction with Cl2 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.How many stereoisomers of 2,4-dibromo-3-chloropentane are there? Draw them, and indicate which are optically active.
cis- and trans-1,4-dimethylcyclohexane in their more stable chair conformations. (a)
How many stereoisomers are there of cis-1,4-dimethylcyclohexane, and how many of trans-1,4-dimethylcyclohexane?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?cis-1,2-Dimethylcyclohexane is optically inactive even though it has two chirality centers. Explain.
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, CH3CH2CH(SH)CH3. Is the stereochemistry of the product R or S?