See image — Isomerism and Stereochemistry Chemistry Question

💡 Solution & Explanation

Sativene is a tricyclic sesquiterpene with molecular formula C15H24. To identify stereogenic (chiral) centers, we look for sp3 carbon atoms bearing four different substituents. Step 1 - Identify the carbon skeleton: Sativene contains a tricyclo[2.2.1.0] type framework (a norbornane-derived tricyclic system) with substituents including a methyl group and an exocyclic methylene (=CH2, making that carbon sp2 and NOT a stereocenter). Step 2 - Exclude sp2 carbons: The carbon bearing the exocyclic =CH2 (isopropenyl/methylene group) is sp2 and therefore cannot be a stereogenic center. Step 3 - Examine the bridgehead and ring-junction carbons: In the sativene skeleton, the bridgehead carbons that are at ring junctions and carry four different carbon substituents are the stereocenters. Analyzing the structure: - The bridgehead carbon bearing the methyl group (lower right) has four different substituents → stereocenter 1. - The bridgehead carbon at the top of the norbornane bridge has four different substituents → stereocenter 2. - The ring-junction carbon connecting the cyclopropane ring to the rest of the framework has four different substituents → stereocenter 3. Step 4 - Count: Three carbons qualify as stereogenic centers. Step 5 - Eliminate other options: Option (a) 2 undercounts the ring-junction stereocenters. Options (c) 4 and (d) 5 overcount by including the sp2 carbon or other carbons that do not bear four distinct substituents. Therefore, the correct answer is B.