JEE Chemistry 2024 Question with Solution

Given: The compound depicted in the image is a cyclohexane derivative with additional alkyl groups attached.

Find: The correct IUPAC name of compound P.

The base structure is a cyclohexane ring. There is one ethyl group attached to the ring, and there are two methyl groups attached to the same carbon atom.

Number the carbon atoms in the ring to give the substituents the lowest possible set of locants. The carbon bearing the two methyl groups is numbered as 1. On continuing the numbering around the ring, the ethyl group gets position 3.

Therefore, the name becomes 3-Ethyl-1,1-dimethylcyclohexane.

Checking the options:

• 1-Ethyl-5,5-dimethylcyclohexane gives a non-minimal numbering.
• 3-Ethyl-1,1-dimethylcyclohexane is correct.
• 1-Ethyl-3,3-dimethylcyclohexane gives incorrect substituent positions.
• 1,1-Dimethyl-3-ethylcyclohexane uses incorrect substituent order.

Therefore, the correct option is B.

Given: A cyclohexane ring with one ethyl substituent and two methyl groups on the same carbon.

Find: The correct IUPAC name.

A quick way is to first assign carbon number 1 to the ring carbon that carries the two methyl groups, because this gives the lowest locants immediately as 1,1. Then choose the direction that gives the ethyl group the smaller number, which is 3.

Hence the compound is named 3-Ethyl-1,1-dimethylcyclohexane. So the correct option is B.