216%20W09-Expt%205 - 216 Winter 09 Notes Dr Masato Koreeda...

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216 Winter 09 Notes - Dr. Masato Koreeda Date: January 22, 2009 Topic : _Experiment 5 __ page 1 of 3. Experiment 5 . The Aldol Reaction (or Condensation) [see: Ege’s 17.4A, pp 701-705] H 3 C H O 2 NaOH H 2 O 5 °C, 1 h H 3 O + workup H 3 C H HO H O H H β α H 3 C H H OH O H H β α + ~50% ( β -hydroxy-aldehyde) Aldol products [ ald ehyde + ol ] Note these specfic reaction conditions. Often difficult to stop at the stage of a β -hydroxy-aldehyde or ketone. Aldol condensation reaction H O H 3 C O NaOH 95% EtOH rt O O + H 2 + H O H 3 C O H In this combination, O C O H H H this is the only "acidic" H (pK a ~18). Note: H O O not acidic base x The resulting carbanion is not stabilized by the C=O π -electrons. orthogonal : no orbital overlap O C O C O H H H HO O O H H O O H H (resonance stabilized) α -hydrogens pK a of H-OH is 15.7 1. 2. Whenever a nucleophilic base (e.g., HO - , H 3 CO - ) is used, the base adds to the C=O carbon. H O O H 3 C O HO HO OH O H O H 3 C O OH However, these adducted compounds are less stable than the original C=O compounds and do not undergo any other reactions but to go back to the original aldehyde/ketone.
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This note was uploaded on 01/31/2010 for the course CHEM 216 taught by Professor Nolta during the Winter '07 term at University of Michigan.

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216%20W09-Expt%205 - 216 Winter 09 Notes Dr Masato Koreeda...

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