See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

Double bond equivalents (DBE), also called degrees of unsaturation, are calculated using the formula: DBE = (2C + 2 + N - H - X) / 2, where C = carbons, N = nitrogens, H = hydrogens, X = halogens. Oxygen and sulfur do not affect the count. Step 1: Determine the molecular formula of amoxicillin. Amoxicillin has the molecular formula C16H19N3O5S. Step 2: Apply the DBE formula. DBE = (2×16 + 2 + 3 - 19) / 2 = (32 + 2 + 3 - 19) / 2 = (18) / 2 = 9 Step 3: Verify by counting structural features. - Benzene ring: 4 DBE (3 C=C + 1 ring) - Amide carbonyl (C=O from side chain): 1 DBE - Beta-lactam carbonyl (C=O in 4-membered ring): 1 DBE - Beta-lactam ring (4-membered ring): 1 DBE - Thiazolidine ring (5-membered ring): 1 DBE - Carboxylic acid (CO2H): 1 DBE Total = 4 + 1 + 1 + 1 + 1 + 1 = 9 DBE Step 4: Why other options fail. - (a) 5 and (b) 6 and (c) 7 all undercount the degrees of unsaturation; they miss contributions from the rings and/or carbonyl groups when tallied carefully. Therefore, the correct answer is D.