Q: A solution of 2.0 g of (+)-glyceraldehyde in 10.0 mL of water was placed in a 100-mm cell. Using the sodium D line, a rotation of +1.74° was found at 25 °C. What is the specific rotation $$[\alpha] of (+)-$$glyceraldehyde?

$$[\alpha] = \frac{+1.74^\circ}{0.2 \times 1} = +8.7^\circ$$

Question 1

Which of the following statements best describes a chiral molecule?

Accepted Answer

A molecule whose mirror image is not superimposable on the original molecule.

Question 2

Which of the following compounds is achiral?

Accepted Answer

trans-1,2-dichlorocyclopentane

Question 3

What is the relationship between maleic acid and fumaric acid?

Accepted Answer

They are geometric (cis-trans) isomers.

Question 4

Which feature is most commonly responsible for chirality in organic molecules?

Accepted Answer

A carbon atom bonded to four different groups.

Question 5

Which of the following statements about enantiomers is correct?

Accepted Answer

Enantiomers have identical melting points, boiling points, and densities.

Question 6

A molecule with two chirality centers can have a maximum of how many stereoisomers?

Accepted Answer

4

Question 7

Which of the following is true about meso compounds?

Accepted Answer

They have asymmetric carbon atoms but are achiral due to a plane of symmetry.

Question 8

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

Accepted Answer

Assign priorities based on decreasing atomic number and orient the lowest priority group away from you.

Question 9

Which of the following statements about optical activity is correct?

Accepted Answer

A racemic mixture is optically inactive.

Question 10

A solution of 2.0 g of (+)-glyceraldehyde in 10.0 mL of water was placed in a 100-mm cell. Using the sodium D line, a rotation of +1.74° was found at 25 °C. What is the specific rotation $$[\alpha] of (+)-$$glyceraldehyde?

Accepted Answer

$$[\alpha] = \frac{+1.74^\circ}{0.2 	imes 1} = +8.7^\circ$$

Question 11

Which of the following is NOT a stereoisomer?

Accepted Answer

Structural isomer

Question 12

Which of the following best explains why (R)-carvone and (S)-carvone have different odors?

Accepted Answer

They interact differently with chiral receptor sites in the nose.

Question 13

Which of the following statements about the physical properties of enantiomers is correct?

Accepted Answer

Enantiomers have identical boiling points and densities.

Question 14

A sample of limonene has an enantiomeric ratio (er) of 97.5:2.5. What is the percent enantiomeric excess (ee)?

Accepted Answer

$$ee = 97.5\% - 2.5\% = 95\%$$

Question 15

Which of the following is a correct statement about racemic mixtures?

Accepted Answer

They contain equal amounts of both enantiomers.

Question 16

Which of the following is a correct application of the 2^n rule for stereoisomers?

Accepted Answer

A molecule with three chirality centers can have up to 8 stereoisomers.

Question 17

Which of the following statements about diastereomers is correct?

Accepted Answer

Diastereomers have different physical and chemical properties.

Question 18

Which of the following is true about the chirality center in 2-butanol?

Accepted Answer

The carbon atom at C2 is bonded to four different groups and is a chirality center.

Question 19

Which of the following best describes the effect of a chiral molecule on plane-polarized light?

Accepted Answer

It rotates the plane of polarized light either clockwise or counterclockwise.

Stereochemistry: Structure, Chirality, and Isomerism in Organic Molecules

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