Q: A sample of 2-bromobutane has a specific rotation of $$-11.55^\circ. $$The literature value for pure $$(S)-2-$$bromobutane is $$-23.1^\circ. $$What is the optical purity of the sample?

$$\frac{-11.55}{-23.1} \times 100\% = 50\%$$

Question 1

Which of the following statements best describes the difference between constitutional isomers and stereoisomers?

Accepted Answer

Constitutional isomers have the same molecular formula but different connectivity of atoms, while stereoisomers have the same connectivity but differ in spatial arrangement.

Question 2

Which of the following molecules is chiral?

Accepted Answer

A molecule with a tetrahedral carbon atom bonded to four different groups.

Question 3

Which of the following best describes a meso compound?

Accepted Answer

A compound with two or more chiral centers and a plane of symmetry, making it achiral.

Question 4

How many stereoisomers are possible for a molecule with three chiral centers?

Accepted Answer

$$2^3 = 8$

Question 5

Which of the following statements about enantiomers is FALSE?

Accepted Answer

Enantiomers are superimposable mirror images.

Question 6

A sample of 2-bromobutane has a specific rotation of $$-11.55^\circ. $$The literature value for pure $$(S)-2-$$bromobutane is $$-23.1^\circ. $$What is the optical purity of the sample?

Accepted Answer

$$\frac{-11.55}{-23.1} 	imes 100\% = 50\%$$

Question 7

Which of the following is NOT a property of diastereomers?

Accepted Answer

They have identical physical properties.

Question 8

Which of the following best describes the Cahn-Ingold-Prelog priority rules for assigning R/S configuration?

Accepted Answer

Assign priorities based on atomic number; if there is a tie, move to the next atom along the chain until a difference is found.

Question 9

A molecule has two chiral centers and is found to be superimposable on its mirror image. What type of compound is this?

Accepted Answer

A meso compound

Question 10

Which of the following statements about conformational isomers is TRUE?

Accepted Answer

They interconvert rapidly at room temperature and cannot be separated.

Question 11

Which of the following is a real-world example where stereochemistry is crucial for biological activity?

Accepted Answer

Thalidomide, where one enantiomer is a sedative and the other is teratogenic.

Question 12

Which of the following statements about optical activity is CORRECT?

Accepted Answer

A racemic mixture does not rotate plane-polarized light.

Question 13

Which of the following is the correct relationship between (2R,3S)-dibromobutane and (2S,3R)-dibromobutane?

Accepted Answer

They are enantiomers.

Question 14

Which of the following is NOT a requirement for a carbon atom to be a chiral center?

Accepted Answer

It must be bonded to four identical groups.

Question 15

A compound has two chiral centers and no plane of symmetry. Which of the following statements is TRUE?

Accepted Answer

It can have both enantiomers and diastereomers.

Question 16

Which of the following best describes the relationship between (R,R)-tartaric acid and meso-tartaric acid?

Accepted Answer

They are diastereomers.

Question 17

Which of the following is TRUE regarding the assignment of R and S configuration?

Accepted Answer

If the lowest priority group is pointing away, trace from 1 to 2 to 3; clockwise is R, counterclockwise is S.

Question 18

Which of the following is a property that enantiomers share?

Accepted Answer

Identical boiling points

Question 19

Which of the following is the correct formula for calculating optical purity?

Accepted Answer

$$	ext{Optical purity} = \frac{[\alpha]_{	ext{sample}}}{[\alpha]_{	ext{pure enantiomer}}} 	imes 100\%$$

Question 20

Which of the following is a correct statement about the relationship between R/S configuration and optical rotation?

Accepted Answer

There is no direct correlation between R/S configuration and the direction of optical rotation.

Chapter 6: Stereoisomers – Stereochemistry and Isomerism in Organic Molecules

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