See image — IUPAC and Nomenclature Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the parent chain/base structure: The compound contains a benzene ring with an aldehyde (–CHO) group attached directly to the ring, making it a benzaldehyde derivative. Step 2 - Identify the principal characteristic group for numbering: The aldehyde (–CHO) group is the principal characteristic group and receives the lowest locant, so the carbon bearing –CHO is C1. Step 3 - Identify substituents and their positions: Looking at the structure, the –Br (bromine) substituent is at the meta position relative to –CHO (C3), and the –SH (thiol/sulpho) group is at the para position relative to –CHO (C4). Step 4 - Note the answer key terminology: The provided correct answer uses 'sulpho' to refer to the –SH (thiol) group at position 4. In the context of this question bank, the –SH group is being named as 'sulpho' (an older or regional naming convention sometimes used in Indian chemistry curricula for –SH groups on benzene). Step 5 - Construct the IUPAC-style name as given: C1 = CHO (benzaldehyde base), C3 = Br (3-bromo), C4 = SH (4-sulpho), giving 3-bromo-4-sulphobenzaldehyde. Step 6 - Why other names fail: Any numbering that gives higher locants to the principal group, or that misidentifies the positions of Br and SH relative to CHO, would be incorrect. Therefore, the correct answer is 3-bromo-4-sulphobenzaldehyde.