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Exam 6: Principles of Stereochemistry

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Question 1

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The structure of the beta-blocker drug Nadolol is given. For the two non-racemic stereocenters, C2 and C3 (labeled), please give the absolute configuration of each.

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For C2, the configur...

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Question 2

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The structures of two of the stereoisomers of tartaric acid are shown. a. Give the structures of all other stereoisomer(s) of tartaric acid on the templates below. You may or may not need all the templates. Put a large "X" through the ones that you do not need, if any. b. What is the stereochemical relationship of each stereoisomer you drew to each of the two stereoisomers shown above? c. What, if anything, can you say about the optical activity of each of the stereoisomers that you drew?

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a. While the (2R,3S)-tartaric acid and (...

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Linezolid is an antibiotic used against gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). It is sold by Pfizer under the trade name Zyvox® as a single enantiomer. a. Mark the asymmetric center with an asterisk (*) in the structure of (−)-linezolid. The Cahn-Ingold-Prelog configuration of the asymmetric center in (−)-linezolid is ___________. b. Assuming that linezolid is synthesized as a racemic mixture, name a method that chemists at Pfizer might be able to utilize to isolate the two enantiomers from racemic linezolid.

Using the templates provided, draw the four possible diastereomers of 1-bromo-2-methylcyclopentane. (You must add the methyl group at a carbon adjacent to the bromine with wedge or dashed wedge bond, as appropriate.) diastereomer 1 (1R,2R)-1-bromo-2-methylcyclopentane diastereomer 2 (1S,2R)-1-bromo-2-methylcyclopentane diastereomer 3 $( 1 R , 2 S )$ -1-bromo-2-methylcyclopentane diastereomer 4 $( 1 S , 2 S )$ -1-bromo-2-methylcyclopentane

A mixture of enantiomers of 5-penten-2-ol has an apparent specific rotation of +9.89º mL g⁻¹ dm⁻¹ at temperature = 25 ºC in ether solvent. The sample is known to have an optical purity (= enantiomeric excess) of 67%. a. What is the specific rotation of the pure S enantiomer under the same conditions? Show your work. b. What percentage of each enantiomer is present in the mixture? Show your work. %S enantiomer:_________________; %R enantiomer: ______________

Identify whether the molecule is chiral or achiral by circling the appropriate work below the structure. Then identify any asymmetric carbons with an asterisk.

Determine the relationship between the two compounds.

The structure of atorvastatin, an important drug used for lowering cholesterol, is shown. (This is sold under the trade name Lipitor with about $13 billion in annual sales.) a. Circle the two asymmetric carbons of atorvastatin and, next to each, give its absolute configuration (R or S). b. What, if anything, can you say about the optical activity of atorvastatin?

Vasotec, a drug prescribed to treat hypertension, is a salt of enalapril cation and maleate anion. a. What is the number of asymmetric centers in Vasotec? b. What is the number of stereocenters in Vasotec? c. There are multiple asymmetric centers in Vasotec. Mark an asymmetric center in the structure of Vasotec above with an asterisk (*). What is the configuration of the asymmetric center you have identified (R/S)? d. What is the configuration of the double bond in maleate anion (E/Z)?

The structure of pseudoephedrine, a common decongestant, is shown below. Compare the structure of pseudoephedrine with the Newman projection of compound X. The relationship between pseudoephedrine and compound X is

Imagine a hypothetical reaction to make a chiral molecule that gives the desired product (the R enantiomer, which has a specific rotation of −80ᵒ mL g⁻¹ dm⁻¹) in 75% EE. Assuming a path length of 1 dm, what would be the observed optical rotation of a solution of 1 g of this 75% EE product mixture dissolved in 1 mL of solvent? (Show your work.) $[ \alpha ] _ { \mathrm { D } } ^ { 20 }$

Select the two chiral compounds in this set.

What is the stereochemistry of the stereoisomeric salt that has the same melting point as this salt? (The numbers refer to the carbons whose stereochemistry is given below.)

Imagine a hypothetical reaction to make a chiral molecule that gives the desired product (the R enantiomer, which has a specific rotation of −55^o mL g⁻¹ dm⁻¹) in 40% EE. What is the specific rotation of the S enantiomer? $[ \alpha ] _ { \mathrm { D } } ^ { 20 }$

Which of the following structures represents a meso compound?

Select the true statements.

Imagine a hypothetical reaction to make a chiral molecule that gives the desired product (the R enantiomer, which has a specific rotation of −95^o mL g⁻¹ dm⁻¹) in 68% EE. What percentage of the product is R, and what percentage is S? (Show your work.) $[ \alpha ] _ { \mathrm { D } } ^ { 20 }$

Identify the stereocenters in the structure.

Enantiomerically pure (S)-2-bromobutane has a specific optical rotation = +23.1ᵒ. A sample of 2-bromobutane containing some of each enantiomer has a specific rotation of −9.2ᵒ. a. The enantiomeric excess of the dominant enantiomer in the mixture is ________________. b. The percentage of the R enantiomer in the mixture is ________________, and the S enantiomer is ________________.

Identify the asymmetric carbons in the structure.