See image — IUPAC and Nomenclature Chemistry Question

💡 Solution & Explanation

Step 1 - Identify the principal characteristic group to determine the parent chain/ring name. The compound contains three substituents on a benzene ring: -OH (hydroxyl), -CN (cyano/nitrile), and -Br (bromo). In IUPAC nomenclature, the principal characteristic group determines the suffix. -CN (nitrile) has higher seniority than -OH as a suffix group when named as benzonitrile. Therefore, the compound is named as a benzonitrile. Step 2 - Number the ring with CN as C1 (the carbon bearing the principal characteristic group gets the lowest locant). The carbon bearing -CN is C1. Looking at the structure: CN is at the bottom-right, Br is at the bottom (adjacent to CN), and OH is at the top (para to Br). Step 3 - Assign locants to substituents. With CN carbon as C1: - CN is at C1 (part of the name 'benzonitrile', no locant needed) - Br is adjacent to CN, so Br is at C2 - OH is para to Br, meaning OH is at C5 (counting from C1: C1=CN, C2=Br, C3=H, C4=H, C5=OH, C6=H) Step 4 - Verify numbering gives lowest locants. Numbering gives Br at 2 and OH at 5, yielding locants {2, 5}. The alternative direction would give Br at 6 and OH at 3, yielding {3, 6}. Comparing sets: {2,5} vs {3,6} — {2,5} is lower at first point of difference (2 < 3), so numbering with Br=2, OH=5 is correct. Step 5 - Construct the name. The name is 2-Bromo-5-hydroxybenzonitrile. Why other options fail: (a) 4-Bromo-3-cyanophenol — uses phenol as parent (OH as principal group) and gives incorrect locants for this structure. (c) 2-Cyano-4-hydroxybromobenzene — incorrect parent name format; bromo cannot be the parent. (d) 6-Bromo-3-hydroxybenzonitrile — uses the higher locant set {3,6} instead of the correct lower set {2,5}. Therefore, the correct answer is B.