Massachusetts Institute of Technology 5.43: Advanced Organic Chemistry Cahn-Ingold-Prelog convention Tetrahedral/sp3 stereocenters: R or S Step 1: Assign priorities to substituents, giving higher priority to atoms of higher atomic number (e.g., S > O > N > C > H) • If there is a "tie," then compare the substituents attached to the groups in question. • If there is a multiple bond, then each formal bond is counted once. • Lone pairs have atomic number 0. Step 2: Place the lowest priority substituent in back. substituents decrease in priority in: • a clockwise direction ⇒ R • a counterclockwise direction ⇒ S 1 4 3 1 2 2 1 3 3 1 2 R 4 2 3 S If the other three

Stereochemistry and Cahn-Ingold-Prelog Convention

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