Ch_322a_7.06

Ch_322a_7.06 - Alkenes by the Dehydrohalogenation of Alkyl...

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Alkenes by the Dehydrohalogenation of Alkyl Halides For synthesis, the E2 reaction is a better choice than the E1 where carbocation intermediates could lead to undesirable rearrangements. Factors that promote the E2 reaction include: use of a secondary or tertiary alkyl halide to slow down nucleophilic substitution. use of a relatively nonpolar or low polarity solvent to slow down the highly polar E1/S N 1 pathway. a high concentration of a strong, relatively nonpolarizable base such as RO - or HO - . Some typical reaction conditions are: sodium ethoxide in ethanol potassium tert-butoxide in tert-butyl alcohol potassium hydroxide in ethanol
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Examples CH 3 CH 2 CH 2 Cl KOH ethanol, heat CH 3 CH=CH 2 + KCl + H 2 O CH 3 CCH 3 CH 3 Br C 2 H 5 ONa ethanol, 55 o C CH 2 =CCH 3 CH 3 + NaBr In these examples, only a single alkene product may be formed. Nucleophilic substitution reactions compete with elimination as already discussed.
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E2 Reactions: Orientation of the Double Bond In most dehydrohalogenation reactions, more than one
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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_7.06 - Alkenes by the Dehydrohalogenation of Alkyl...

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