Q: Which of the following statements about Fischer projections is CORRECT?

Rotating a Fischer projection by $180^\\circ$ in the plane of the paper retains the same compound.

Question 1

Which of the following statements about enantiomers is TRUE?

Accepted Answer

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

Question 2

A compound has two stereocenters. How many possible stereoisomers can it have, assuming no symmetry?

Accepted Answer

$2^2 = 4$

Question 3

Which of the following best describes a meso compound?

Accepted Answer

A compound with stereocenters that is achiral due to an internal plane of symmetry.

Question 4

A racemic mixture contains:

Accepted Answer

Equal amounts of both enantiomers and is optically inactive.

Question 5

Which of the following is NOT a property of diastereomers?

Accepted Answer

They have identical physical properties.

Question 6

If a solution of a chiral compound rotates plane-polarized light by $+25^\circ$, what is the observed rotation for a racemic mixture of the same compound?

Accepted Answer

$0^\circ$

Question 7

Which of the following statements about Fischer projections is CORRECT?

Accepted Answer

Rotating a Fischer projection by $180^\circ$ in the plane of the paper retains the same compound.

Question 8

A sample contains $70\%$ of the $(R)$ enantiomer and $30\%$ of the $(S)$ enantiomer. What is the enantiomeric excess (ee)?

Accepted Answer

$40\%$

Question 9

Which of the following best explains why enantiomers can be distinguished by biological molecules?

Accepted Answer

Biological molecules are chiral and interact differently with each enantiomer.

Question 10

Which of the following is TRUE regarding the separation of enantiomers and diastereomers?

Accepted Answer

Diastereomers can be separated by standard laboratory techniques, but enantiomers cannot.

Question 11

A compound has three stereocenters. If one of the stereocenters is the same in two molecules, but the other two are opposite, what is the relationship between the two molecules?

Accepted Answer

They are diastereomers.

Question 12

Which of the following is a requirement for a molecule to be chiral?

Accepted Answer

It must not be superimposable on its mirror image.

Question 13

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

Accepted Answer

They have identical physical properties except for the direction of optical rotation.

Question 14

If a compound is optically inactive but contains stereocenters, what is the most likely explanation?

Accepted Answer

It is a meso compound.

Question 15

Which of the following is TRUE about the interaction of enantiomers with plane-polarized light?

Accepted Answer

Each enantiomer rotates plane-polarized light in equal magnitude but opposite directions.

Question 16

A solution contains $60\%$ $(S)$ and $40\%$ $(R)$ enantiomer. What is the optical rotation if the pure $(S)$ enantiomer rotates light by $+20^\circ$?

Accepted Answer

$+4^\circ$

Question 17

Which of the following is a correct statement about the use of polarimeters in stereochemistry?

Accepted Answer

Polarimeters measure the rotation of plane-polarized light by chiral compounds.

Question 18

Which of the following is the correct formula for calculating enantiomeric excess (ee)?

Accepted Answer

$ee = |\%\ 	ext{major enantiomer} - \%\ 	ext{minor enantiomer}|$

Question 19

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

Accepted Answer

They are enantiomers.

Question 20

Which of the following is TRUE about the chemical reactivity of enantiomers?

Accepted Answer

They react identically with achiral reagents but differently with chiral reagents.

Stereoisomers: Structure, Properties, and Projections

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