See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Step 1: Identify the compound. The structure shown is 1,2,4,5-tetramethylcyclohex-2-ene (or equivalently described as a cyclohexene with methyl groups at four positions). Looking carefully at the structure: there is a six-membered ring with one double bond, and four methyl groups. The double bond carbons (C1 and C2, say) each bear one methyl group — these are sp2 carbons and are NOT stereocenters. The remaining two sp3 carbons bearing methyl groups (C4 and C5, or whichever two saturated carbons carry methyls) are the potential stereocenters. Step 2: Identify stereocenters. Only the two sp3 ring carbons that each carry a methyl group are potential stereocenters. The sp2 (double bond) carbons cannot be stereocenters. So we have 2 stereocenters. Step 3: Apply the 2^n formula cautiously. With n = 2 stereocenters, the maximum number of stereoisomers = 2^2 = 4. However, we must check for meso forms due to molecular symmetry. Step 4: Check for symmetry / meso compounds. The molecule has a plane of symmetry consideration. With the double bond fixed in the ring and the two sp3 methyl-bearing carbons, we need to enumerate: (R,R), (S,S), (R,S), and (S,R). Due to the symmetry of the ring (the two stereocenters are related by the plane of symmetry passing through the double bond midpoint and the opposite bond), the (R,S) and (S,R) configurations represent the same meso compound. So (R,S) = (S,R) = 1 meso compound, (R,R) = 1 enantiomer, (S,S) = 1 enantiomer. Step 5: Count total stereoisomers. We get: (R,R), (S,S) as one enantiomeric pair, and one meso form. Total = 3 stereoisomers. Step 6: Why other options fail. Option (a) 2 is wrong because it ignores the meso form. Options (c) 32 and (d) 64 are vastly too large — they would require 5 or 6 stereocenters, which this molecule does not have. Therefore, the correct answer is B.