Kharasch

Part of speech: noun

Definitions

1. A chemical reaction named after the American chemist Morris Selig, in which hydrogen bromide adds across a double bond in anti-Markovnikov fashion
2. The peroxide-initiated addition of hydrogen bromide to an alkene, named for the American chemist Morris Selig who studied it
3. A radical addition process credited to the American chemist Morris Selig, where HBr attaches to the less substituted carbon of an alkene

Etymology: Kharasch is a surname, and the reaction bears the name of Morris Selig Kharasch, the American chemist who studied it at the University of Chicago. The word itself is therefore a person's name turned into a technical term: a "Kharasch addition" is a reaction in which a reagent adds across a double bond in a way that places the new group on the carbon with more hydrogen atoms, the opposite of the outcome predicted by the older rule for these additions. Kharasch's work centred on the effect of peroxides, which were found to reverse the expected orientation of addition, most famously with hydrogen bromide. Chemists later spoke of "anti-Markovnikov" addition, a label that works as a contrast with the earlier Markovnikov rule, but "Kharasch addition" is the name used when the peroxide-initiated, radical-driven pathway is the focus.