page_title: Hemiacetal
section_title: Formula and formation
hierarchical_section_title: Hemiacetal / Formula and formation
context_page_description: A hemiacetal or a hemiketal is a compound that results from the addition of an alcohol to an aldehyde or a ketone, respectively. The Greek word hèmi, meaning half, refers to the fact that a single alcohol has been added to the carbonyl group, in contrast to acetals or ketals, which are formed when a second alkoxy group has been added to the structure.
context_section_description: The general formula of a hemiacetal is R¹R²C(OH)OR,where R¹ or R² is often hydrogen and R (bonded to O) is not hydrogen.
  While in the IUPAC definition of a hemiacetal R₁ or R₂ may or may not be a hydrogen, in a hemiketal none of the R-groups can be a hydrogen. Hemiketals are regarded as hemiacetals where none of the R-groups are H, and are therefore a subclass of the hemiacetals.
caption: Above: 1-ethoxybutan-1-ol, a hemiacetal. Below: 1,1-diethoxybutan, an acetal