Lecture26CHM233final(10)

Lecture26CHM233final(10) - Organic Chemistry Third Edition...

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1 Organic Chemistry, Third Edition Janice Gorzynski Smith University of Hawai’i Chapter 15 Radical Reactions
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2 A radical is a reactive intermediate with a single unpaired electron, formed by homolysis of a covalent bond. A radical contains an atom that does not have an octet of electrons. Half-headed arrows are used to show the movement of electrons in radical processes. Radicals
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3 Carbon radicals are classified as 1°, 2°, or 3° . A carbon radical is sp 2 hybridized and trigonal planar , like carbocations. The unhybridized p orbital contains the unpaired electron and extends above and below the trigonal planar carbon. Structure of Radicals
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4 Stability of Radicals (like cabocations) Figure 15.1
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5 Radicals are formed from covalent bonds by adding energy in the form of heat ( ! ) or light ( h " ) . Some radical reactions are carried out in the presence of a radical initiator such as peroxides, RO–OR . Radicals undergo two main types of reactions – they react with # bonds, and they add to $ bonds. General Features of Radical Reactions
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6 A radical X• rapidly reacts with whatever is available, like a # or $ bond. A radical X• abstracts a hydrogen atom from a C–H # bond to form H–X and a carbon radical. Reaction of a Radical X• with a C–H Bond
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7 A radical X• adds to the $ bonds. Reaction of a Radical X• with a C=C Bond In radical reactions (with a # or $ bond) a new radical is created.
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Two radicals can react to form a sigma bond. An example is the reaction of a radical with oxygen (O 2 is a diradical in its ground state electronic configuration). Reaction with O 2 causes a radical chain reaction to slow down or stop; X–O–O• radicals are not as reactive as halogen radicals. Compounds that prevent radical reactions from occurring are called radical inhibitors or radical scavengers. Inhibition of Radicals by O
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This note was uploaded on 01/03/2012 for the course CHEM 233 taught by Professor Anamoore during the Fall '10 term at ASU.

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Lecture26CHM233final(10) - Organic Chemistry Third Edition...

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