- 2067 Mangsir · 4 marks
Enantiomers, racemic mixture, meso compound
Short answer
Enantiomers are non-superimposable mirror images, like (+)- and (−)-lactic acid, each optically active with opposite rotation. A racemic mixture is an equimolar mixture of enantiomers, e.g. (±)-lactic acid, optically inactive by external compensation. A meso compound like meso-tartaric acid has chiral centres but an internal symmetry plane, rendering it inactive.
Define enantiomers, racemic mixture and meso compound giving one example of each. Also comment on their optical activity.
| Term | Definition | Example | Optical activity |
|---|---|---|---|
| Enantiomers | Pair of stereoisomers that are non-superimposable mirror images | (+)- and (−)-lactic acid | Active; equal in magnitude and opposite in direction |
| Racemic mixture | Equimolar mixture of two enantiomers (written ±) | (±)-lactic acid, (±)-tartaric acid | Inactive, because rotations cancel (external compensation) |
| Meso compound | Compound with two or more chiral centres but with an internal plane of symmetry (achiral) | meso-tartaric acid | Inactive, because the rotation of one half cancels the other (internal compensation) |
Racemic mixtures can be resolved into the active enantiomers; meso compounds cannot, as they are a single compound.
✓ Answer checked by Claude Opus 5.5 (high effort)
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