Ch_322a_6.016

Ch_322a_6.016 - Factors Influencing the Rates of the SN1...

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Factors Influencing the Rates of the S N 1 and S N 2 Reactions The S N 1 and S N 2 are always potentially competitive pathways for any nucleophilic substitution reaction. However, because of structural, electronic, and other factors, one pathway usually dominates. Effect of Structure on the S N 1 and S 2 2 Reactions A change in alkyl group substitution around the reacting carbon influences nucleophilic substitution by the S N 1 and S N 2 mechanisms in opposite ways. The S N 2 Mechanism Increasing alkyl substitution slows down this reaction: R-X + Nu: - R = methyl > primary > secondary >> tertiary fastest R- Nu + X: - A special case of a primary alkyl bromide that does not react readily by the S N 2 mechanism is neopentyl bromide . CH 3 -C-CH 2 Br CH 3 CH 3 "neopentyl bromide" 1-bromo-2,2-dimethylpropane
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An Example: Incorporation of isotopic bromine in RBr Relative second-order rate constants in acetone at 25 o C for the S N 2 reaction: Br - * isotope label + R-Br Br -R * + Br - acetone R = CH 3 - CH 3 CH 2 - CH 3 CH CH 3 CH 3
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This note was uploaded on 07/22/2009 for the course CHEM 322AL taught by Professor Jung during the Summer '07 term at USC.

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Ch_322a_6.016 - Factors Influencing the Rates of the SN1...

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