9-WedNov7HLSF07.ppt

9-WedNov7HLSF07.ppt - Br NaOEt EtOH 55 o C + NaBr + EtOH...

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Vinyl and aryl halides do not undergo S N 2 because C C H Cl R H Nu X Br Nu X Vinyl and aryl halides do not undergo S N 1 because RCH CH Cl RCH CH X + Cl - Br X + Br -
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Bruice, P. Organic Chemistry 4th Ed.
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When an alkyl halide can undergo either S N 1 or S N 2 these factors will determine which reaction will predominate : •the concentration of the nucleophile, •the reactivity of the nucleophile, •the solvent of the reaction An S N 2 reaction is favored by a high/low concentration of a poor/good nucleophile in a aprotic/protic solvent. An S N 1 reaction is favored by a high/low concentration of a poor/good nucleophile and a aprotic/protic donor solvents
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Some Biological Methylating Reagents
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In addition to substitution, an alkyl halide can undergo an elimination reaction Elimination reactions useful for synthesis of alkenes When X= halogen = dehydrohalogenation
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Unformatted text preview: Br NaOEt EtOH 55 o C + NaBr + EtOH 79% I. The E2 Reaction - bimolecular (like S N 2) A. Mechanism: H Br H H H H HO B. Stereochemistry of E2 Reaction The bonds to the eliminated groups (H and X) must be antiperiplanar : in the anti conformation - in the same plane X H Example: Cl CH 3 H 3 C Et H H OR Antiperiplanar requirement important for cyclohexane derivatives. Which molecule do you predict would react faster with RO by E2 mechanism? H Br H Br Br Br Br B. The Regioselectivity of the E2 Reaction The major product of an E2 reaction is (usually) the most stable alkene (Zaistevs rule) Recall: the greater the number of substituents, the more stable is the alkene therefore: Why? you ask Reaction Coordinate Diagram Br CH 3 O CH 3 OH...
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This note was uploaded on 05/13/2010 for the course CHEM 151L taught by Professor Roy,christopher during the Fall '08 term at Duke.

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9-WedNov7HLSF07.ppt - Br NaOEt EtOH 55 o C + NaBr + EtOH...

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