How do you assign R or S to a stereocentre? This video builds up the Cahn–Ingold–Prelog (CIP) rules one at a time: atomic number first, then how to break a tie, how to count double bonds, and what to do when the lowest-priority group points toward you. The examples get harder as we go, from bromochlorofluoromethane to carvone and ephedrine, which has two stereocentres. Each rule has its own chapter, so you can jump back to the one you need.
Chapters
0:00 An exam question
0:26 The method in four steps
0:51 Finding the stereocentre
1:30 Rule one: atomic number
2:06 Reading in 3D
2:30 Rule two: break the tie
3:09 Atoms, not size
3:46 Going further out
4:19 Rule three: double bonds
5:03 Putting it together: carvone
6:04 When group four points the wrong way
6:36 Two stereocentres: ephedrine
7:39 Checklist
Sources
– Cahn, R. S., Ingold, C. & Prelog, V. (1966). Specification of molecular chirality. Angew. Chem. Int. Ed. Engl. 5, 385–415.
– Favre, H. A. & Powell, W. H. (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013, section P-92. Royal Society of Chemistry.
Molecule models are computed geometries. Every R/S label in the video was checked against RDKit.
Narration is an AI voice; script, chemistry and visuals are written and checked by a chemistry lecturer.
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