What is a diastereomer?

A stereoisomer that is not identical to, and is not a mirror image of, the other stereoisomer being compared.

How do enantiomers differ from one another at stereocenters?

For corresponding stereocenters, enantiomers have opposite configurations at every center.

One of a pair of diastereomers that differ in configuration at exactly one stereocenter.

What do syn and anti mean in a suitable zigzag projection?

Syn means the specified groups are on the same face; anti means they are on opposite faces. These descriptors express relative, not absolute, stereochemistry.

How are erythro and threo distinguished in the relevant Fischer projection?

Erythro has the two identical substituents on the same side; threo has them on opposite sides.

Organic chemistryLesson 1 of 1 in the course Stereochemistry

Diastereomers: Classification, Relative Descriptors, and Chemical Consequences

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

This lesson introduces diastereomers and distinguishes them from enantiomers. It also explains epimers and two naming systems—syn/anti and erythro/threo—that describe relative stereochemistry in particular structures.

Stereoisomers have the same molecular connectivity but differ in the three-dimensional arrangement of their atoms. Diastereomers are stereoisomers that are not identical and are not mirror images of one another.

All flashcards

What is a diastereomer?: A stereoisomer that is not identical to, and is not a mirror image of, the other stereoisomer being compared.
How do enantiomers differ from one another at stereocenters?: For corresponding stereocenters, enantiomers have opposite configurations at every center.
What is an epimer?: One of a pair of diastereomers that differ in configuration at exactly one stereocenter.
What do syn and anti mean in a suitable zigzag projection?: Syn means the specified groups are on the same face; anti means they are on opposite faces. These descriptors express relative, not absolute, stereochemistry.
How are erythro and threo distinguished in the relevant Fischer projection?: Erythro has the two identical substituents on the same side; threo has them on opposite sides.

Quiz questions

What distinguishes a diastereomeric pair from an enantiomeric pair?Answer: Diastereomers are nonidentical stereoisomers that are not mirror images.
When are two diastereomers specifically called epimers?Answer: When they differ in configuration at exactly one stereocenter.
Two structures have configurations $R,R,S$ and $R,S,S$ . How are they related?Answer: They are epimers because they differ at one stereocenter.
In a suitable zigzag projection, what does anti indicate about the specified groups?Answer: They lie on opposite faces of the projection.
In the relevant Fischer projection, how are identical substituents arranged in a threo isomer?Answer: They are on opposite sides of the projection.

Based on the Wikipedia article Diastereomer, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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