Q: The specific rotation $$[\alpha] of a $$compound is calculated using which formula?

$$[\alpha] = \frac{\alpha(\text{observed})}{c \cdot l}$$

Q: A solution of 6 g of 2-butanol in 40 mL solution is placed in a 200-mm polarimeter tube and gives an observed rotation of $$-4.05^{\circ}. $$What is the specific rotation $$[\alpha]$$?

$$[\alpha] = \frac{-4.05}{0.15 \times 2} = -13.5$$^{\circ}$$

Question 1

Which of the following statements best describes a chiral molecule?

Accepted Answer

A molecule whose mirror image is not superimposable on itself.

Question 2

Which of the following compounds is achiral?

Accepted Answer

A molecule with a plane of symmetry.

Question 3

Which of the following is true about enantiomers?

Accepted Answer

They have identical physical properties except for their interaction with plane-polarized light and other chiral molecules.

Question 4

A carbon atom is considered a chirality center if:

Accepted Answer

It is bonded to four different groups.

Question 5

Which of the following best describes a racemic mixture?

Accepted Answer

A mixture containing equal amounts of both enantiomers.

Question 6

The specific rotation $$[\alpha] of a $$compound is calculated using which formula?

Accepted Answer

$$[\alpha] = \frac{\alpha(	ext{observed})}{c \cdot l}$$

Question 7

A solution of 6 g of 2-butanol in 40 mL solution is placed in a 200-mm polarimeter tube and gives an observed rotation of $$-4.05^{\circ}. $$What is the specific rotation $$[\alpha]$$?

Accepted Answer

$$[\alpha] = \frac{-4.05}{0.15 	imes 2} = -13.5$$^{\circ}$$

Question 8

Which of the following is NOT a property of diastereomers?

Accepted Answer

They are mirror images of each other.

Question 9

How many stereoisomers are possible for a molecule with three chiral centers, assuming no plane of symmetry?

Accepted Answer

8

Question 10

Which of the following statements about meso compounds is correct?

Accepted Answer

Meso compounds have a plane of symmetry and are achiral.

Question 11

Which of the following is the correct sequence for assigning priorities in the Cahn-Ingold-Prelog system?

Accepted Answer

Assign priorities based on atomic number; higher atomic number gets higher priority.

Question 12

A compound rotates plane-polarized light clockwise. Which term describes this property?

Accepted Answer

Dextrorotatory (+)

Question 13

Which of the following best explains why only one enantiomer of alanine is metabolized by enzymes in the human body?

Accepted Answer

Enzymes are chiral and only recognize one enantiomer.

Question 14

Which of the following is true about the optical activity of a racemic mixture?

Accepted Answer

It does not rotate plane-polarized light.

Question 15

Which of the following molecules can be chiral even though it does NOT have a chiral carbon?

Accepted Answer

Allene with different groups at each end.

Question 16

Which of the following is a correct statement about Fischer projections?

Accepted Answer

A 180° rotation in the plane of the paper does not change the configuration.

Question 17

A mixture of (R)- and (S)-2-iodobutane has a specific rotation of $$-3.18^{\circ}. If $$the specific rotation of pure (S)-2-iodobutane is $$+15.90^{\circ}$$, what is the percentage of the (R)-enantiomer in the mixture?

Accepted Answer

40%

Question 18

Which of the following is a practical method for separating enantiomers in a racemic mixture?

Accepted Answer

Reacting with a pure chiral compound to form diastereomers.

Question 19

Which of the following best describes the relationship between cis- and trans-1,2-dimethylcyclopentane?

Accepted Answer

They are diastereomers.

Stereochemistry: Chirality, Enantiomers, Diastereomers, and Optical Activity

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