Chapter 3 Multiple Choice Questions

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. In low doses, aspirin is used clinically for its antiplatelet properties.

Which of the following structures, shown below, is a constitutional isomer of aspirin?

Structure 1 correct incorrect

Structure 2 correct incorrect

Structure 3 correct incorrect

Structure 4 correct incorrect

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. Ethambutol is one part of a combination cocktail for the treatment of TB. Consider the plot below representing energy against dihedral angle of the central ethyl group in ethambutol and identify the incorrect statement.
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Point 1 corresponds to structure B and is a preferred staggered conformation. correct incorrect

Point 2 corresponds to structure D and is the most stable conformation. correct incorrect

Point 3 corresponds to a staggered gauche conformation. correct incorrect

Point 4 corresponds to structure A and is a conformation of low stability. correct incorrect

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. The main conformations that can be adopted by the cyclohexane ring of the CNS stimulant, methylphenidate, are shown below. Choose the correct statement relating to the preferred conformation.

Structure 2 is less stable than structure 4. correct incorrect

Structure 3 is more stable than structure 1. correct incorrect

Structure 4 is more stable than structure 3. correct incorrect

Structure 2 is less stable than structure 1. correct incorrect

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. Clomifene is used to treat ovulatory failure in women who want to become pregnant. Study the structure below, and decide which statement is true

Clomifene has 11 π bonds. correct incorrect

The structure shown above is the E isomer of clomifene. correct incorrect

Clomifene has 1 chiral carbon. correct incorrect

The E and Z isomers of clomifene will have identical chemical properties. correct incorrect

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. The structure of paclitaxel, an anticancer agent, is shown below. Study the structure to identify the chiral carbon atoms in paclitaxel and choose the correct statement.

There are 9 chiral centres in paclitaxel. correct incorrect

There are 10 chiral centres in paclitaxel. correct incorrect

There are 11 chiral centres in paclitaxel. correct incorrect

There are 12 chiral centres in paclitaxel. correct incorrect

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. The structure of the active isomer of doxycycline, an antibiotic, is shown below. Identify the correct statement about the stereochemistry of doxycycline.

There are six defined stereogenic carbon atoms in doxycycline with 12 possible stereoisomers. correct incorrect

The stereochemistry can be correctly assigned at C5 as (R). correct incorrect

One alkene can be correctly assigned as Z and the other as E. correct incorrect

The stereochemistry can be correctly assigned at C4 as (S). correct incorrect

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. Consider the four isomers of C₁₃H₁₆ClNO shown below and choose the incorrect statement.

Structures 1 and 4 are conformational isomers. correct incorrect

Structure 2 is a constitutional isomer of structure 1. correct incorrect

Structures 1 and 3 are identical. correct incorrect

Structures 3 and 4 are enantiomers. correct incorrect

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. The active enantiomers of four pharmaceuticals are illustrated below. Assign the stereochemistry of each structure as R or S, as appropriate, and then choose the correct statement.

Levalbuterol and Dexketoprofen have the same stereochemical assignment. correct incorrect

Levobupivacaine and Dexketoprofen show the same stereochemistry. correct incorrect

Dexketoprofen has the same stereochemistry as Levocetirizine. correct incorrect

Three structures show S stereochemistry and 1 shows R stereochemistry. correct incorrect

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. Fischer nomenclature is still commonly used for sugars and amino acids; it uses the D and L assignment of stereochemistry. Which of the following statements about Fischer projections is incorrect?

Fischer projections are drawn as 2D representations of chiral molecules. correct incorrect

The carbon skeleton is drawn vertically with the most oxidised carbon atom at the top of the structure. correct incorrect

An OH or NH₂ group on the right of the carbon chain indicates R-stereochemistry. correct incorrect

Rotation of the whole Fischer projection by 90^o inverts the stereochemistry. correct incorrect

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. Chloramphenicol is a broad-spectrum antibiotic that is commonly used topically – in the form of eye drops or eye ointment – to treat superficial eye infections. From the structure below, deduce how many stereoisomers can exist for chloramphenicol.

2 Stereoisomers correct incorrect

3 Stereoisomers correct incorrect

4 Stereoisomers correct incorrect

5 Stereoisomers correct incorrect