91Ó°ÊÓ

A tetrahedral atom bonded to four different groups is called a stereogenic center.

In a stereogenic center, if two atoms are exchanged, an isomer is obtained.

The presence of a stereogenic center is the primary criterion for a compound to show optical activity.

It is also called a chiral center or asymmetric center.

Stereogenic centers are present only in tetrahedral atoms.

Therefore, any sp³ carbon attached to four different groups can be considered as stereogenic center in amines.

Quaternary ammonium salts are also tetrahedral. Therefore, they can also be stereogenic centers if they have four different substituents.

a. It does not have any tetrahedral carbon with different substituents. There is two quarternium nitrogen. One of them has different substituents. Therefore, the compound has one stereogenic center.

Compound a with a circled chiral center

b. The compound does not have any quaternium amine. One sp³ carbon atom has different substituents. Therefore, the compound has one stereocenter.

Compound b with chiral atom circled