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Enantiomers vs diastereomers
Short answer
Enantiomers are non-superimposable mirror images with identical physical properties and opposite optical rotation. Diastereomers are stereoisomers that are not mirror images, have different physical properties. Example: tartaric acid's (R,R) and (S,S) forms are enantiomers; meso-tartaric acid is a diastereomer of each.
Distinguish between enantiomers and diastereomers. Give an example to support your answer.
Enantiomers vs diastereomers
| Basis | Enantiomers | Diastereomers |
|---|---|---|
| Relationship | Stereoisomers that are non-superimposable mirror images | Stereoisomers that are not mirror images |
| Number of chiral centres | One or more (all centres inverted) | Usually two or more (only some inverted); cis–trans isomers are also diastereomers |
| Physical properties | Identical (m.p., b.p., solubility) | Different |
| Chemical properties | Same with achiral reagents | Different |
| Optical rotation | Equal in magnitude, opposite in sign | Different, unrelated values |
| Separation | Difficult (needs resolution) | Easy (crystallisation, distillation) |
| Example | (+)- and (−)-lactic acid; (2R,3R)- and (2S,3S)-tartaric acid | (2R,3R)-tartaric acid and meso-tartaric acid |
Example: tartaric acid has three forms: (2R,3R), (2S,3S) and meso (2R,3S). The (R,R) and (S,S) forms are enantiomers (mirror images). The meso form is a diastereomer of each, because it is not their mirror image, and it has a different m.p. (140 °C vs 170 °C for the active forms) and solubility.
✓ Answer checked by Claude Opus 5.5 (high effort)
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