Q: Which of the following is the correct formula for specific rotation?

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

Question 1

Which of the following molecules is most likely to be chiral?

Accepted Answer

A molecule with a tetrahedral carbon bonded to four different substituents

Question 2

Which statement best describes enantiomers?

Accepted Answer

They are non-superimposable mirror images of each other

Question 3

Which of the following groups cannot serve as a chirality center in organic molecules?

Accepted Answer

A carbon atom in a CH2 group

Question 4

Which of the following best explains why lactic acid is chiral?

Accepted Answer

Its central carbon is bonded to four different groups and lacks a plane of symmetry

Question 5

Which of the following statements about optical activity is TRUE?

Accepted Answer

Optically active compounds rotate plane-polarized light

Question 6

A solution of (+)-lactic acid has a specific rotation $$[\alpha]_D = +3.82. $$What is the specific rotation of (−)-lactic acid?

Accepted Answer

$$[\alpha]_D = -3.82$$

Question 7

Which of the following best describes the relationship between R/S configuration and optical rotation?

Accepted Answer

There is no simple correlation between R/S configuration and the direction or magnitude of optical rotation

Question 8

Which of the following is the correct formula for specific rotation?

Accepted Answer

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

Question 9

If the concentration of an optically active sample is doubled and the pathlength is kept constant, what happens to the observed rotation?

Accepted Answer

The observed rotation doubles

Question 10

Pasteur’s discovery of enantiomers involved which of the following observations?

Accepted Answer

He separated two kinds of crystals that were non-superimposable mirror images and found their solutions to be optically active with equal and opposite specific rotations

Question 11

According to the Cahn–Ingold–Prelog sequence rules, which group ranks highest when attached to a chirality center?

Accepted Answer

The atom with the highest atomic number

Question 12

Which of the following statements about the assignment of R and S configuration is correct?

Accepted Answer

If the lowest-ranked group is oriented away from the observer, and the sequence from highest to lowest (1 → 2 → 3) is clockwise, the configuration is R

Question 13

Which of the following molecules is achiral?

Accepted Answer

Propanoic acid, because it has a plane of symmetry

Question 14

Which scenario would result in a racemic mixture being optically inactive?

Accepted Answer

A 50:50 mixture of two enantiomers, each with equal and opposite specific rotations

Question 15

Which of the following is NOT a consequence of the Cahn–Ingold–Prelog sequence rules?

Accepted Answer

The sign of optical rotation is determined by the R/S configuration

Question 16

Which of the following best describes the physical properties of enantiomers?

Accepted Answer

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

Question 17

A polarimeter is used to measure which property of a compound?

Accepted Answer

The angle of rotation of plane-polarized light

Question 18

Which of the following would NOT be considered a chirality center?

Accepted Answer

A carbon atom in a C=O group

Question 19

Which of the following is TRUE regarding the effect of wavelength on optical rotation?

Accepted Answer

The angle of rotation depends on the wavelength of light used

Stereochemistry at Tetrahedral Centers: Chirality, Enantiomers, and Optical Activity

Study Guide - Practice Questions

Study Guide - Flashcards