Question

How many aldehydic groups does the compound phthaldehyde have?

(a) 1

(b) 2

(c) 3

(d) 4

This question was posed to me in an internship interview.

Question is taken from Nomenclature and Structure of Carbonyl Groups topic in division Aldehydes, Ketones and Carboxylic Acids of Chemistry – Class 12

Answer 1

Right option is (b) 2

To explain I would say: Phthaldehyde is an aromatic compound containing two CHO groups, one on each adjacent carbon of the benzene ring. To give equal importance to both the aldehydic groups, it is named as benzene-1,2-dicarbaldehyde in the IUPAC system.