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picture1_Aldol Condensation Ppt 82155 | Chem 14cl Lecture 5b Aldol


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File: Aldol Condensation Ppt 82155 | Chem 14cl Lecture 5b Aldol
introduction functional group pk the acidity of organic compounds is often determined a by neighboring groups because they can help stabilizing alkane 50 the resulting anion i e halogen nitro ...

icon picture PPTX Filetype Power Point PPTX | Posted on 09 Sep 2022 | 3 years ago
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                                             Introduction
                                                                                       Functional group      pK
        •    The acidity of organic compounds is often determined                                               a
             by neighboring groups because they can help stabilizing                   Alkane                 ~50
             the resulting anion (i.e., halogen, nitro, etc.) because of               Ester                  ~25
             their electronegative character or due to resonance                       Aldehyde/ketone     ~18-20
             (i.e., enolate in carbonyl compounds)                                     Alcohol             ~15-19
                                                                                       Nitro                ~8-10
        •    For instance, the presence of a carbonyl group greatly increases the acidity of 
             neighboring hydrogen atoms (a-protons) because of the resonance stabilization in the 
             resulting enolate ion (the numbers in parentheses below are from acetone, AM1) 
             127.8 pm
           (123.5 pm)
                             137.4 pm
                           (149.5 pm)
        •    Many of the carbonyl compounds can be deprotonated with moderately strong bases i.e., 
             hydroxide, alcoholates, etc.
                           Aldol Condensation
       • Ketones and aldehydes can be reacted with each other 
           in Aldol or Claisen-Schmidt condensation:
                           H         H         -       O    OH      T         O
                               +            [OH]                                           Aldol
                         O         O                 H                      H
                       Ph   H          H Self condensation of acetaldehyde  to 
                                                        O    OH                 O
                                          form crotonaldehyde also called "aldol"
                                                -                     T
                                +            [OH]
                          O         O                 H        Ph             H        Ph
                                              Formation of cinnamaldehyde
                     Theory for the Experiment I
        • In Chem 14CL, acetone is reacted with two equivalents 
            of benzaldehyde using sodium hydroxide as catalyst:
                                                                                 O
                                   CHO
                                            O     NaOH(aq.)/EtOH
                        2              +                                                             + 2H2O
        • The first step is the formation of the first enolate ion:
                                      O                       O               O
                                                                                         +  H O
                                      C C    + –                                           2
                                                OH            C C             C C
                                        H
                                                                    enolate ion
        • Note that water is one of the products in the enolate formation 
             the amount of water has to be minimized in order to optimize 
            the amount of enolate in the reaction mixture.
             Theory for the Experiment II
      •   The enolate ion acts as the nucleophile, which attacks the 
          carbonyl group of the benzaldehyde to form the new C-C bond:
      •   The trans, trans-isomer is primarily formed and isolated in the 
          reaction.
      Running the Reaction
  • Acetone is reacted with two equivalents of 
   benzaldehyde in a small Erlenmeyer flask.
  • An aqueous ethanolic solution of sodium 
   hydroxide is added slowly (drop wise) while 
   stirring. 
  • The mixture is stirred for 30 minutes.
  • The crude product precipitates as a yellow 
   solid from the solution during the reaction.
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...Introduction functional group pk the acidity of organic compounds is often determined a by neighboring groups because they can help stabilizing alkane resulting anion i e halogen nitro etc ester their electronegative character or due to resonance aldehyde ketone enolate in carbonyl alcohol for instance presence greatly increases hydrogen atoms protons stabilization ion numbers parentheses below are from acetone am pm many be deprotonated with moderately strong bases hydroxide alcoholates aldol condensation ketones and aldehydes reacted each other claisen schmidt h o oh t ph self acetaldehyde form crotonaldehyde also called formation cinnamaldehyde theory experiment chem cl two equivalents benzaldehyde using sodium as catalyst cho naoh aq etoh ho first step c note that water one products amount has minimized order optimize reaction mixture ii acts nucleophile which attacks new bond trans isomer primarily formed isolated running small erlenmeyer flask an aqueous ethanolic solution added ...

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