Final answer:
Optical isomerism, or enantiomerism, occurs in organic compounds with chiral carbon atoms. Optical isomers are mirror images of each other and cannot be superimposed. To determine optical isomerism, look for the presence of a chiral carbon, which causes rotation of plane-polarized light in opposite directions.
Step-by-step explanation:
Optical isomerism, also known as enantiomerism, refers to a type of isomerism that arises due to the presence of an asymmetric (chiral) carbon atom in a molecule. Chiral carbons are those that are bonded to four different groups or atoms. Optical isomers exist as mirror images of each other and cannot be superimposed.
To determine whether an organic compound exhibits optical isomerism, you need to identify the presence of a chiral carbon. If a molecule has a chiral carbon, it will exhibit optical activity and rotate plane-polarized light in either a clockwise (dextro) or counterclockwise (levo) direction.
In the case of 1-bromo-1-chloroethane, the compound is optically active because it contains a chiral carbon. On the other hand, 1-bromo-2-chloroethane does not exhibit optical activity as it lacks a chiral carbon.