Hemiacetal - Definition and Overview

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, and can dissociate 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