See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

Step 1 - Concept: Isomers have the same molecular formula. We need to determine the molecular formula of each compound and identify which one differs. Step 2 - Analyze compound (a): Cyclooctene is an 8-membered ring with one double bond. Molecular formula: C8H14. Degree of unsaturation (DoU) = (2×8+2-14)/2 = (18-14)/2 = 2. Wait, let me recalculate: For C8H14, DoU = (2×8+2-14)/2 = (16+2-14)/2 = 4/2 = 2. One ring + one double bond = 2. That fits C8H14. Step 3 - Analyze compound (b): Two cyclobutane rings connected by a single bond (cyclobutylcyclobutane or bicyclobutane). Two cyclobutane rings each C4H8, connected: C8H14 with two rings and no double bonds. DoU = 2 (two rings). Molecular formula C8H14. This is an isomer of (a). Step 4 - Analyze compound (c): Two fused cyclopentane rings (bicyclo[3.3.0]octane / pentalene). This has 8 carbons and two rings. Molecular formula: C8H14. DoU = 2 (two rings). This is an isomer of (a) and (b). Step 5 - Analyze compound (d): The structure appears to be a tricyclic compound with a central 4-membered ring fused to two cyclopropane rings (like tricyclo structure). This looks like bicyclo[1.1.0]butane fused arrangement or a structure with three rings. Counting carbons: the central ring (4C) fused with two cyclopropane rings sharing edges - this gives a tricyclic system. If it is tricyclo[2.2.0.0^{2,6}]... let me count: the image shows what appears to be two triangles fused to a central 4-membered ring. Carbon count: a central 4-membered ring sharing one bond with each of two cyclopropane rings. Shared atoms mean: 4 + 2 + 2 = 8 carbons but with shared edges, actual count = 6 carbons. With 3 rings and 6 carbons: C6H8 or similar. Three rings = DoU of 3 minimum. For C6H8: DoU = (2×6+2-8)/2 = (14-8)/2 = 3. This matches 3 rings. So compound (d) has molecular formula C6H8, while (a), (b), (c) have C8H14. Compound (d) is NOT an isomer of the others. Step 6 - Why other options fail: (a), (b), and (c) all have molecular formula C8H14 with DoU = 2, making them isomers of each other. Compound (d) has a different molecular formula (fewer carbons, different hydrogen count), so it cannot be an isomer. Therefore, the correct answer is D.