A hemiacetal is a functional group or compound containing the function group in the form of: In ecology functional groups are collections of organisms based on morphological, physiological, behavioral, biochemical, or environmental responses or on trophic criteria. ...

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. In general usage, alcohol (from Arabic al-khwl الكحول, or al-ghawl الغول) refers almost always to ethanol, also known as grain alcohol, and often to any beverage that contains ethanol (see alcoholic beverage). ... An acetal is a functional group or molecule containing the functional group of a carbon bonded to two -OR groups. ... An aldehyde is either a functional group consisting of a terminal carbonyl group, or a compound containing a terminal carbonyl group. ... In general usage, alcohol (from Arabic al-khwl الكحول, or al-ghawl الغول) refers almost always to ethanol, also known as grain alcohol, and often to any beverage that contains ethanol (see alcoholic beverage). ...

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

An aldehyde dissolved in water exists in equilibrium with low concentrations of its hydrate [R-CH(OH)2]. Similarly, in excess alcohol, the aldehyde, its hemiacetal, and its acetal all exist in solution. Nucleophilic addition involves the addition of a nucleophile to a chemical compound. ... A carboxyl or carboxylic group is a functional group consisting of a carbon atom and an oxygen atom doubly bonded to each other. ... An aldehyde is either a functional group consisting of a terminal carbonyl group, or a compound containing a terminal carbonyl group. ... A ketone is either the functional group characterized by a carbonyl group linked to two other carbon atoms or a compound that contains this functional group. ... In general usage, alcohol (from Arabic al-khwl الكحول, or al-ghawl الغول) refers almost always to ethanol, also known as grain alcohol, and often to any beverage that contains ethanol (see alcoholic beverage). ... An acid (often represented by the generic formula AH) is typically a water-soluble, sour-tasting chemical compound. ... The common (Arrhenius) definition of a base is a chemical compound that either donates hydroxide ions or absorbs hydrogen ions when dissolved in water. ... Nucleophilic addition involves the addition of a nucleophile to a chemical compound. ... In general usage, alcohol (from Arabic al-khwl الكحول, or al-ghawl الغول) refers almost always to ethanol, also known as grain alcohol, and often to any beverage that contains ethanol (see alcoholic beverage). ... An acid (often represented by the generic formula AH) is typically a water-soluble, sour-tasting chemical compound. ... An acetal is a functional group or molecule containing the functional group of a carbon bonded to two -OR groups. ... Drinking water This article focuses on water as we experience it every day. ...

Hemiacetal results from addition of alcohol's hydroxyl group to carbon in C=O bond. Acetals are products of substitution reactions catalyzed by acid. Presence of acid improves leaving capacity of hydroxyl group and enables its substitution with alkoxyl group (-OR). Coversion of hemiacetal to acetal is an SN1 reaction.

Ketones give hemiketals and ketals. These do not form as readily as hemiacetals and acetals. To increase yields of ketals or acetals water molecules that form during reaction can be removed.

Hemiacetals and hemiketals are unstable compounds. In some cases, stable cyclic hemiacetals and hemiketals can be readily formed. Glucose, for example, exists as a cyclic hemiacetal.