Hemiacetal and Acetal Functional Groups - PowerPoint PPT Presentation

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Hemiacetal and Acetal Functional Groups

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Hemiacetal and Acetal Functional Groups Hemiacetal: alcohol and ether on same carbon Acetal: Two ethers on same carbon Mechanism Must be acid-catalyzed. – PowerPoint PPT presentation

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Title: Hemiacetal and Acetal Functional Groups


1
Hemiacetal and Acetal Functional Groups
  • Hemiacetal alcohol and ether on same carbon
  • Acetal Two ethers on same carbon

2
Mechanism
  • Must be acid-catalyzed.
  • Adding H to carbonyl makes it more reactive with
    weak nucleophile, ROH.
  • Hemiacetal forms first, then acid-catalyzed loss
    of water, then addition of second molecule of ROH
    forms acetal.
  • All steps are reversible.
    gt

3
Hemiacetal Synthesis aldehyde alcohol
  • Alcohol aldehyde --gt hemiacetal
  • Ethanal methanol
  • Alcohol oxygen becomes an ether
  • Carbon double bond oxygen becomes an alcohol

4
Mechanism for Hemiacetal
5
Aldehyde and Ketone Reactions
6
Synthesis of Acetal Functional Group
  • Acetal alcohol plus hemiacetal (ether synthesis)
  • Acetal Two ethers on same carbon

7
gt
8
Aldehyde and Ketone Reactions
9
Mechanism Hemiacetal to Acetal
10
Cyclic Acetals
  • Addition of a diol produces a cyclic acetal.
  • Sugars commonly exist as acetals or hemiacetals.
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