Question

Identify the correct IUPAC name of the following compound.

(a) 3-Methylcyclopent-2-en-1-one

(b) 1-Methylcyclopent-1-en-3-one

(c) Cyclo-1-methyl-pent-1-en-3-one

(d) Cyclo-3-methyl-pent-2-en-1-one

The question was asked in an internship interview.

I need to ask this question from Nomenclature and Structure of Carbonyl Groups in portion Aldehydes, Ketones and Carboxylic Acids of Chemistry – Class 12

Answer 1

Correct answer is (a) 3-Methylcyclopent-2-en-1-one

To elaborate: This is a cyclic ketone with a double bond and a substituted methyl group. In this compound the keto carbon will be given the lowest number. Hence, the double bond is at second carbon and methyl group at the third carbon. It is named as a substituted cyclopentanone.