Enantiomer vs Diastereomer

Quick Answer

Enantiomers are mirror images that you cannot superimpose. Diastereomers are stereoisomers that are not mirror images at all.

What Each One Really Means

Stereochemistry is where many students start to panic, but let me make it simple. Both enantiomers and diastereomers are stereoisomers. They have the same molecular formula and the same connectivity, but different spatial arrangements. The difference is in the relationship. Enantiomers are mirror images of each other. Think of your left hand and your right hand. You cannot rotate one to look exactly like the other. Non-superimposable. Diastereomers are stereoisomers that are not mirror images. Think of your left hand and your left foot. Related, but not mirror images. Now this is what really matters in practice. Enantiomers have almost identical physical properties. Same boiling point, same melting point, same density. The only thing that differs is how they interact with plane-polarized light and with other chiral molecules. That is why separating enantiomers is so hard. Diastereomers, on the other hand, have different physical properties. Different boiling points, different solubilities. So you can separate them by ordinary methods like distillation or crystallization. This is actually the trick behind resolving enantiomers. You react the enantiomer mixture with a pure chiral reagent, and that converts them into diastereomers. Then you separate them by normal means. Then you convert them back. Understand the relationship first, and the separation will follow.

Side-by-Side Comparison

Memory Device

Enantiomers are left and right hands. Diastereomers are left hand and left foot.

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