Question

Which of the following molecules is expected to rotate the plane polarised light?

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

The plane of polarised light is rotated by optically active compound. These compounds are called optical isomers. Major criteria for a molecule to be optically active is to be a chiral compound.
Chiral compounds has asymmetric carbon atom where all the 4 substituents are different.

In the given compounds, (a) has asymmetrical carbon and it is a chiral molecule. Thus, it is optically active. Hence, it will rotate plane polarised light.

In compound (b), there is no chiral carbon.
In compound (c), there is a symmetry in the molecule. Hence, it is optically inactive.
In compound (d), there is no chiral carbon.