The Hemiacetal reference article from the English Wikipedia on 24-Apr-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Hemiacetal

A hemiacetal is a functional group or compound containing the function group in the form of:

where R and R' are any carbon backbones.

A hemiacetal can react with an alcohol under very acidic conditions to form an acetal, can hydrolyse to form an aldehyde and an alcohol.

Reactions

Synthesis

1. Nucleophilic addition of an alcohol to a carboxyl group
   • aldehyde or ketone + alcohol + acid (catalyst) or base (catalyst) ↔ hemiacetal
     • Nucleophilic addition of an alcohol to a resonance stabilized hemiacetal cation
       • hemiacetal + alcohol + acid (catalyst) ↔ acetal + water

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