The formyl group is a functional group in organic chemistry. It has the chemical formula −C=OH. It is the simplest carbonyl functional group. Compounds where formyl groups are attached to hydrogen or carbon atoms are called aldehydes. Heteroatom formyl compounds are derivatives of formic acid.
The name "formyl" is not commonly used in chemical nomenclature. Systematic names prefer to use the suffix form, aldehyde, unless more senior groups are on the molecule. When more senior groups are on the molecule, the prefix form oxo- is used rather than "formylalkyl" for side chains (e.g. oxobutyl, not formylpropyl). This leaves "formyl" only for −COH substituents right next to the main structure of a molecule that has a more senior group.
