Read the passage carefully and answer the Questions.
Aldehydes, carboxylic acids and ketones are widespread in the animal and plant kingdoms. They play a pivotal role in various biochemical processes of life. Their presence in nature adds fragrance and flavor. These compounds are widely used in food products, pharmaceuticals, paints, resins and other important product industries. These compounds are prepared by various laboratory methods, which mainly include oxidation, formylation, acylation and reduction. Due to the polar nature of the carbonyl group in aldehydes and ketones, they can exhibit different reactions like nucleophilic addition. They do exhibit redox and various condensation reactions which lead to the formation of various important compounds. On the other hand, the carboxylic acids are mainly prepared by oxidation and hydrolysis of different compounds. The carboxylic acid consists of a carbonyl group and the hydroxy group (attached to the carbonyl carbon atom). This makes it possible for the carboxylic acid to participate in various chemical reactions which involve cleavage of the C-OH bond and the O-H bond along with the reactions involving the complete -COOH group.
The IUPAC name of following compound is
\( OHC-C_6H_4-CHO-p \)
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Benzene-1,4-dicarbaldehyde
In IUPAC names the suffix “-al” is used only when the carbon of the –CHO group is part of the parent chain (as in ethanal or butanal). When the –CHO group is attached to a ring, its carbon cannot be counted in the ring, so the suffix “-carbaldehyde” is added to the name of the ring. That is why benzaldehyde is benzenecarbaldehyde.
The given compound, \( \ce{OHC-C6H4-CHO} \) (p), has two –CHO groups on a benzene ring at positions 1 and 4. Both are principal groups, so both are shown in the suffix with the multiplying prefix “di” and their locants: benzene-1,4-dicarbaldehyde.
Why the other options are incorrect
Option (1) Benzene-1,4-dial — Incorrect. The ending “-dial” would mean that the two carbonyl carbons are part of the parent; here they sit outside the ring.
Option (2) 1,4-Dioxobenzene — Incorrect. The prefix “oxo” stands for an =O on a ring carbon itself, as in a quinone; it does not describe –CHO groups.
Option (3) 4-Formylbenzaldehyde — Incorrect. It treats one –CHO group as the principal group and the other as a substituent; when identical principal groups are present, all of them are cited in the suffix.
NCERT (2026-27 edition):
Nomenclature – “… When the aldehyde group is attached to a ring, the suffix carbaldehyde is added after the full name of the cycloalkane. The numbering of the ring carbon atoms start from the carbon atom attached to the aldehyde group. The name of the simplest aromatic aldehyde carrying the aldehyde group on a benzene ring is benzenecarbaldehyde. However, the common name benzaldehyde is also accepted by IUPAC.”
Note: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| – | 30-05 S2 16-05 S1 | – | – | – |