Question

Explain why the enantiomers of 1,2-dimethylaziridine can be separated even though one of the “groups” attached to nitrogen is a lone pair.

Short answer

In this compound nitrogen is in sp² hybridization. But it don’t have an angle of 120°. In the transition state of amine inversion the nitrogen atom is sp² hybridized so the bond angle is 120°. A nitrogen is three membered ring cannot achieve a bond angle of 120°. So the amine inversion that would interconvert the enantiomers cannot occur. Therefore the enantiomers can’t be separated.

Step-by-step solution

What is enantiomer

Pair of enantiomers will exist if the compound has asymmetric centre or a chiral carbon. So the mirror images of compounds don’t superimpose.

Chiral objects are those objects which have no same mirror images. The mirror images don’t superimpose each other. whose mirror images superimpose each other that compounds are called achiral objects.

Final answer

In the transition state of amine inversion the nitrogen atom is sp² hybridized so the bond angle is 120°. A nitrogen is three membered ring cannot achieve a bond angle of 120°. So the amine inversion that would interconvert the enantiomers cannot occur. Therefore the enantiomers can’t be separated.