See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Step 1: Analyze compound (C). Compound (C) is 1-(1-methylethylidene)-3-methylcyclohexane, more precisely it is (ethylidene)cyclohexane with a methyl substituent at C3. The structure shows a cyclohexane ring with an exocyclic double bond at C1 (=CH-CH3, i.e., the carbon bears one H and one CH3) and a CH3 group at C3. Step 2: Identify stereocenters and sources of stereoisomerism in (C). - The exocyclic double bond C1=CH-CH3: This is a trisubstituted alkene. The C1 of the ring is connected to two ring carbons (C2 and C6), and the exocyclic carbon bears H and CH3. This gives geometric (E/Z) isomerism about the exocyclic double bond: E and Z isomers exist. - C3 of the ring bears CH3, H, and two different ring segments (since C1 has the exocyclic double bond making C2 side different from C4 side). C3 is a stereocenter, giving R and S configurations. - Therefore, stereoisomers of (C): E/Z × R/S = 2 × 2 = 4 stereoisomers. Step 3: Analyze compound (D). Cyclohexene (C6H10) reacts with H2/Ni (catalytic hydrogenation) to give cyclohexane (C6H12) as the major product. This is a straightforward syn addition of H2 across the double bond. Step 4: Calculate degree of unsaturation (DoU) of (D). Cyclohexane has molecular formula C6H12. DoU = (2×6 + 2 - 12) / 2 = (12 + 2 - 12) / 2 = 2/2 = 1. The ring itself accounts for 1 degree of unsaturation. Step 5: Calculate the sum. Number of stereoisomers of (C) = 4 Degree of unsaturation of (D) = 1 Sum = 4 + 1 = 5. Therefore, the correct answer is 5.