Q: Which of the following is the correct formula for calculating the specific rotation $$[\alpha]_D of an $$optically active compound?

$$[\alpha]_D = \frac{\alpha}{l \times c}$$

Question 1

Which of the following statements best explains why lactic acid is chiral while propanoic acid is achiral?

Accepted Answer

Lactic acid has four different groups attached to its central carbon, while propanoic acid does not.

Question 2

Which of the following molecules would NOT be expected to rotate plane-polarized light?

Accepted Answer

A racemic mixture of (+)- and (−)-lactic acid

Question 3

Which of the following best describes an enantiomer?

Accepted Answer

A molecule that is not superimposable on its mirror image

Question 4

A student is given a sample of 2-methylcyclohexanone. Which property can be used to confirm its chirality?

Accepted Answer

It rotates plane-polarized light.

Question 5

Which of the following is the correct formula for calculating the specific rotation $$[\alpha]_D of an $$optically active compound?

Accepted Answer

$$[\alpha]_D = \frac{\alpha}{l 	imes c}$$

Question 6

Which of the following best describes a molecule that is achiral?

Accepted Answer

It has a plane of symmetry in any conformation.

Question 7

A solution of camphor is placed in a polarimeter and is found to rotate plane-polarized light to the right. How is this rotation described?

Accepted Answer

Dextrorotatory, with a plus sign (+)

Question 8

Which of the following molecules is chiral?

Accepted Answer

5-Bromodecane

Question 9

Which of the following is a correct statement about the relationship between enantiomers?

Accepted Answer

They have identical physical properties except for the direction in which they rotate plane-polarized light.

Question 10

A chemist isolates two crystalline forms of sodium ammonium tartrate, one dextrorotatory and one levorotatory. What is the relationship between these two forms?

Accepted Answer

They are enantiomers.

Question 11

Which of the following best explains why a racemic mixture does not rotate plane-polarized light?

Accepted Answer

The optical activities of the two enantiomers cancel each other out.

Question 12

Which of the following is a necessary condition for a carbon atom to be a stereocenter (chiral center)?

Accepted Answer

It must be attached to four different groups.

Question 13

Which of the following molecules would be expected to have a plane of symmetry?

Accepted Answer

Methylcyclohexane

Question 14

A sample of (+)-lactic acid has a specific rotation of $$+32.0^\circ. If $$the path length is $$2 dm $$and the concentration is $$0.5 g/cm$^3$$, what is the observed rotation $$\alpha$$?

Accepted Answer

$$\alpha = [\alpha]_D 	imes l 	imes c = 32.0 	imes 2 	imes 0.5 = 32.0^\circ$$

Question 15

Which of the following best describes the relationship between the left and right hands as shown in the mirror image diagram?

Accepted Answer

They are non-superimposable mirror images, analogous to enantiomers.

Question 16

Which of the following is true about the optical activity of a solution containing only one enantiomer of a chiral compound?

Accepted Answer

It will rotate plane-polarized light in a specific direction.

Question 17

Which of the following best explains why norbornane is classified as a polycyclic molecule?

Accepted Answer

It contains more than one ring structure fused together.

Question 18

Which of the following is a real-world application of chirality in organic chemistry?

Accepted Answer

The effectiveness and safety of many drugs depend on their chirality.

Question 19

Which of the following statements about the use of a polarimeter is correct?

Accepted Answer

A polarimeter measures the angle by which plane-polarized light is rotated when passing through a solution of an optically active compound.

Cycloalkanes and Stereochemistry: Chirality, Enantiomers, and Optical Activity

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