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Three-Dimensional Representations

Assigning Priorities

Determining Stereochemical Relationships

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Definitions: Rotation of Light

Enantiomers rotate light by equal amounts, but in opposite directions. (One enantiomer is the d enantiomer and the other enantiomer is the l enantiomer.) Experiments or calculations can be used to determine which way a molecule will rotate a plane of polarized light.

For example, consider the following molecules.

These molecules are enantiomers of glyceraldehyde. (Check for yourself that they are mirror images and non-superimposable.) The molecule on the left is the l enantiomer of glyceraldehyde, and the molecule on the right is the d enantiomer of glyceraldehyde. Therefore, these molecules will rotate light by the same amount, but in different directions.

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