CHEM 203 Lecture Notes - Lecture 12: Halonium Ion, Alkene, Nucleophile
Document Summary
The question of regioselectivity in the sn2-like reaction of unsymmetrical halonium ions, e. g. propene: a simple unsymmetrical. A nucleophile, nu (=electron-rich species, therefore electrostaticallly negative), will be attracted to the site of greater + character, so one may predict that it will preferentially attack carbon atom b. Principle: an external nucleophile will attack an unsymmetrical chloronium (bromonium, halonium) ion preferentially at the carbon that can sustains the greatest fraction of positive charge (= the more highly polarized c atom) Driving force in the above reactions: the electronegative halogen atoms, initially in an unfavorable oxidation state of 0, are reduced to the favorable oxidation state of 1. Reactions of alkenes with other agents that incorporate an electronegative atom in a high oxidation state: the case of elemental oxygen. Principle: elemental oxygen, o2, can (and does) react with alkenes, but through mechanisms that we have not yet covered in chem 203 and that will be discussed in the near future.
