CH2CHO

CH2CHO is a small, carbon-centered radical with the chemical formula C2H3O. It is commonly described as a formylmethyl radical, consisting of a formyl group (CHO) bonded to a methylene unit (CH2) and bearing an unpaired electron, typically localized on the methylene carbon (CH2•–CHO).

The radical arises in gas-phase reactions involving acetaldehyde (CH3CHO) and related hydrocarbons, via hydrogen abstraction by radicals such as H, OH, or O, or by photolysis of larger aldehydes. It is a transient intermediate in combustion chemistry and is also discussed in astrochemical models as part of reaction networks in space environments.

In chemical kinetics, CH2CHO participates in oxidation and chain-propagating steps, including reactions with molecular oxygen to form peroxy derivatives and reactions with hydrogen to reform acetaldehyde. It can also add to unsaturated hydrocarbons to form larger carbonyl-containing species. Studying CH2CHO helps constrain detailed mechanisms of hydrocarbon oxidation and the formation of aldehydes in flames and, potentially, in interstellar processes.

CH2CHO has been detected and characterized in laboratory experiments using spectroscopic techniques that probe its rotational and electronic structure, such as microwave spectroscopy and laser-based methods. These measurements support identification in gas-phase experiments and aid in modeling reactive combustion and astrochemical pathways. As a reactive intermediate, CH2CHO remains short-lived and is typically studied under controlled, high-temperature or low-temperature conditions to elucidate its behavior.