See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Concept: C7H14 has the molecular formula corresponding to one degree of unsaturation (DoU = (2×7+2-14)/2 = 1), which means one ring or one double bond. Since we restrict to only 5-membered ring cycloalkanes, we need cyclopentane (C5H10) as the base ring with the remaining 2 carbons attached as substituents. Step 1: Identify the base ring. A cyclopentane ring uses 5 carbons; we have 7 total, so 2 carbons remain as substituents (as alkyl groups) attached to the ring. Step 2: Enumerate ways to attach 2 carbons to cyclopentane as alkyl substituents. Case A: One substituent containing both carbons = one ethyl group on cyclopentane. - Ethylcyclopentane: 1 isomer (all ring positions equivalent for monosubstitution) Case B: Two separate methyl groups (each substituent is CH3) on cyclopentane = dimethylcyclopentane. - The two methyl groups can be placed on the ring at different relative positions: 1,1-dimethylcyclopentane: both methyls on the same carbon → 1 isomer 1,2-dimethylcyclopentane: methyls on adjacent carbons → cis and trans stereoisomers → 2 isomers 1,3-dimethylcyclopentane: methyls separated by one carbon → cis and trans stereoisomers → 2 isomers (1,4 and beyond on a 5-membered ring are equivalent to 1,2 or 1,3 by symmetry, so no new constitutional isomers) Step 3: Count all structural and stereoisomers. - Ethylcyclopentane: 1 - 1,1-dimethylcyclopentane: 1 - 1,2-dimethylcyclopentane (cis): 1 - 1,2-dimethylcyclopentane (trans): 1 - 1,3-dimethylcyclopentane (cis): 1 - 1,3-dimethylcyclopentane (trans): 1 That gives 1+1+2+2 = 6 so far. Wait — re-examining: the question asks for total isomers including stereoisomers, giving 8. Re-check: 1,2-dimethylcyclopentane trans has two enantiomers (R,R and S,S) that are non-superimposable, so it counts as 2 distinct stereoisomers. Similarly, 1,3-dimethylcyclopentane trans has two enantiomers counting as 2. - Ethylcyclopentane: 1 - 1,1-dimethylcyclopentane: 1 - cis-1,2-dimethylcyclopentane: 1 (meso-like, achiral) - trans-1,2-dimethylcyclopentane: 2 (R,R and S,S enantiomers) - cis-1,3-dimethylcyclopentane: 2 (two enantiomers, R,S pair) - trans-1,3-dimethylcyclopentane: 1 (achiral, meso) Total: 1+1+1+2+2+1 = 8 Therefore, the correct answer is 8.