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Unformatted text preview: CHAPTER 15 Radical Reactions 15.1 Introduction and General Features of Radical Reactions Radicals are species that have an unpaired electron. Because radicals do not have a full octet of electrons, they are electron-deficient and usually highly reactive. Radicals are neutral; they have no formal charge. Because radicals are electrically neutral, a solvent is not necessary for radical reactions (unlike in reactions involving ions where a solvent is required to dissolve the ionic species). There are two general types of free-radical reactions in organic chemistry: substitution and addition . In the generation of radicals, a half-headed arrow is used to show the movement of each electron ( fish-hook ). All radical reactions are chain reactions; the reaction proceeds in a series of discrete steps. Radical reactions proceed through 3 general steps: initiation , propagation , termination . A reaction usually involves radicals if any of these reactants or conditions are present: AIBN (a radical initiator) , peroxides (ROOR) , UV light (h) , or high temperature (300-500C) . Compounds that prevent radical reactions from occurring are called radical inhibitors or radical scavengers ( e.g. O 2 , Vitamin E , Antioxidants ). Done by Dr. Felix N. Ngassa for CHM 242: Organic Chemistry for Life Sciences 2, GVSU, Spring/Summer 2011. 1 A. Geometry: A carbon radical has a trigonal planar geometry with bond angles of 120 about the carbon with the unpaired electron. Carbon radicals are classified as primary (1), secondary (2), or tertiary (3) by the number of carbons ( R groups ) directly bonded to the carbon with the unpaired electron. B. Hybridization: A carbon radical is sp 2 hybridized....
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