Question

Which of the following is optically active
A. Ethylene glycol
B. Oxalic acid
C. Glycerol
D. Tartaric acid

Answer 1

Hint: The compound which rotates the plane polarised light in a clockwise or in an anticlockwise direction is called an optically active compound. For a compound to be optically active it must contain at least one chiral carbon.

Complete answer:The optical activity of any compound can be determined by passing the plane-polarised light through the compound, if the compound rotates the plane-polarised light in a clockwise direction it is called dextrorotatory and if the compound rotates the plane-polarised light in an anti-clockwise direction it is called levorotatory. For a compound to be optically active compound must contain a chiral carbon or a chiral center, a chiral carbon is a carbon that is attached to four different substituents and a chiral center is a stereogenic center containing four different substituents.

The structures of the given compounds are –
1. Ethylene glycol


In ethylene glycol, we can see that there is no chiral carbon because with both the carbons two hydrogens are attached.
2. Oxalic Acid


In oxalic acid, we can see that there is no chiral carbon because oxygen is attached with a double bond with both carbons.
3. Glycerol


In glycerol as well there is no chiral carbon because CH2OH is a common substituent attached to the center carbon.
4. Tartaric Acid



In tartaric acid, we can see that there are two chiral carbons so tartaric acid is optically active.

Thus, Option (D) is correct

Note: Tartaric acid have three optical isomerism. D- tartaric acid, l- tartaric acid and meso- tartaric acid. Among these three isomers D- tartaric acid and l- tartaric acid are optically active and meso- tartaric acid is optically inactive.