Formyl (2597-44-6) Physical and Chemical Properties
Formyl
One-carbon carbonyl radical (formyl, HCO•) commonly used as a reactive fragment in mechanistic studies, gas‑phase chemistry, and method development for R&D and analytical workflows.
| CAS Number | 2597-44-6 |
| Family | Formyl radical (carbonyl fragment) |
| Typical Form | Reactive gaseous species |
| Common Grades | EP |
Formyl is the one-carbon carbonyl radical with molecular formula \(\ce{CHO}\). It is an open‑shell, monovalent radical derived formally from formaldehyde by removal of one hydrogen: the unpaired electron resides principally on the carbon atom with π-interaction to the carbonyl oxygen. Structurally the fragment is the smallest representative of acyl radicals and exhibits the electronic features of a carbonyl group (partial double-bond character) combined with radical reactivity (highly electrophilic and short-lived under ordinary conditions).
Because it is an open‑shell species of very low molecular weight, formyl exists in practice as a transient gas‑phase or matrix‑isolated intermediate rather than a stable, isolable compound. It has effectively no rotatable bonds, low complexity and a small topological polar surface area, but the radical and polar carbonyl motifs produce reactivity that dominates phase behavior and partitioning. Acid–base chemistry is not applicable in the conventional sense (no stable protonation equilibria as an isolated radical); under condensed‑phase conditions rapid reactions (hydration, hydrogen atom abstraction, recombination, oxidation) control its fate rather than classical solubility equilibria.
Common commercial grades reported for this substance include: EP.
Basic Physical Properties
Density
No experimentally established value for this property is available in the current data context. As a small gaseous radical under ambient conditions, bulk density is not a meaningful material specification; gas‑phase partial density when generated depends on the generation method and conditions.
Melting Point
No experimentally established value for this property is available in the current data context. The formyl radical is not an isolable crystalline material under standard laboratory conditions.
Boiling Point
No experimentally established value for this property is available in the current data context. The entity behaves as a transient gas‑phase species at temperatures where it is formed.
Vapor Pressure
No experimentally established value for this property is available in the current data context. Vapor‑pressure descriptions are not applicable to an unstable radical that is normally observed only transiently in the gas phase or in low‑temperature matrices.
Flash Point
No experimentally established value for this property is available in the current data context. The formyl radical is not handled as a bulk liquid and flash‑point testing is not applicable.
Chemical Properties
Solubility and Phase Behavior
The formyl radical is a very small, gas‑phase reactive intermediate; it does not have a stable, meaningful solubility value in conventional solvents. In contact with condensed phases it is rapidly consumed by bimolecular reactions (hydrogen abstraction, radical recombination, addition to unsaturated systems) or by reaction with dissolved O2 to form peroxy intermediates. Predictions based on computed descriptors (topological polar surface area 17.1; hydrogen‑bond acceptor count 1) indicate limited polar surface area, but the radical nature and high reactivity make standard partitioning or equilibrium solubility descriptors of limited practical use.
Reactivity and Stability
The defining feature is its open‑shell electronic structure: high chemical reactivity toward radical traps, molecular oxygen, unsaturated bonds, and hydrogen donors. Typical reaction channels include recombination to closed‑shell carbonyl products, oxidation to formyl peroxy species in the presence of O2, and hydrogen‑atom abstraction or transfer. The species is thermally and chemically unstable under ambient conditions and is typically observed only under gas‑phase, plasma, flame, or matrix isolation conditions or produced in situ at very low steady‑state concentrations in radical reaction systems.
Thermodynamic Data
Standard Enthalpies and Heat Capacity
No experimentally established value for this property is available in the current data context. Thermochemical characterization of transient radicals is normally obtained from high‑level electronic structure calculations or specialized spectroscopic/kinetic studies rather than routine bulk calorimetry.
Molecular Parameters
Molecular Weight and Formula
- Molecular formula: \(\ce{CHO}\)
- Molecular weight: 29.018 (reported) — units: \(\mathrm{g}\,\mathrm{mol}^{-1}\)
- Exact mass: 29.002739651
- Monoisotopic mass: 29.002739651
Additional computed descriptors: heavy atom count 2; complexity 2; formal charge 0; rotatable bond count 0; topological polar surface area 17.1.
SMILES: [CH]=O
InChI: InChI=1S/CHO/c1-2/h1H
InChIKey: CFHIDWOYWUOIHU-UHFFFAOYSA-N
LogP and Polarity
- XLogP3‑AA (computed): 1.2
The computed XLogP value indicates modest predicted lipophilicity for a neutral small fragment, but practical partitioning behavior for a radical is dominated by reactivity and short lifetime. The TPSA of 17.1 and a single hydrogen‑bond acceptor site reflect the presence of the carbonyl oxygen; however, hydrogen‑bonding interactions in solution are transient because the radical rapidly undergoes chemical reactions rather than establishing equilibrium solvation.
Structural Features
Formyl is a planar (sp2‑like) carbonyl fragment with an unpaired electron delocalized between the carbon and the oxygen to some extent; resonance stabilization by the oxygen atom partially stabilizes the radical center but does not confer long‑term persistence. The fragment contains only two heavy atoms (C and O) and one hydrogen, giving minimal steric shielding. Conformer generation using standard molecular mechanics methods is not applicable because of unsupported atom valence for a radical electronic structure in those force fields.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS: 2597-44-6
- ChEBI ID: CHEBI:29327
- Nikkaji number: J247.870F
- Wikidata: Q27110014
SMILES: [CH]=O
InChI: InChI=1S/CHO/c1-2/h1H
InChIKey: CFHIDWOYWUOIHU-UHFFFAOYSA-N
Synonyms and Structural Names
Depositor‑supplied synonyms and labels found in registration metadata include:
Formyl; 2597-44-6; RefChem:1085542; Formyl radical; hydridooxidocarbon(.); HCO(.); CHEBI:29327
(Additional deprecated or removed synonym strings are present in historical annotations but are not reproduced here as primary synonyms.)
Industrial and Commercial Applications
Representative Uses and Industry Sectors
As an isolated bulk substance, formyl is not a commercial product. Its relevance to industry is as a transient reactive intermediate encountered in gas‑phase chemistry, combustion and flame chemistry, atmospheric oxidation processes, and mechanistic studies of radical reactions. It is of interest to researchers modeling oxidation pathways of one‑carbon compounds and to those studying radical chain mechanisms.
Role in Synthesis or Formulations
Formyl functions principally as a short‑lived intermediate in synthetic radical chemistry and in mechanistic pathways rather than as a reagent or formulation component. In synthetic contexts it can be generated in situ under controlled conditions to probe reaction kinetics or to effect single‑electron transfer steps; it is not available or used as a stable, shipped material.
Safety and Handling Overview
Acute and Occupational Toxicity
The formyl radical itself is an extremely reactive transient species rather than a conventional toxicant with established exposure limits. Occupational and acute hazards associated with systems that generate formyl include exposure to reactive carbonyls (for example formaldehyde), combustion products, and oxidants. When generated, the radical can participate in chain reactions that produce secondary toxic or irritating species; appropriate engineering controls, respiratory protection, and avoidance of uncontrolled exposures are required when working with processes that produce radical intermediates.
Storage and Handling Considerations
Formyl is not stored as a bulk material; it must be generated and consumed in situ if required for experimental or process chemistry. Handling considerations therefore focus on control of generation points: use of inert atmospheres where appropriate, elimination of ignition sources, containment to prevent release of related volatile carbonyls, and scrubbing or quenching of effluent streams. Standard laboratory and industrial hygiene practices should be applied: local exhaust ventilation, appropriate personal protective equipment, and procedures to minimize worker exposure to reactive intermediates and their by‑products. For detailed hazard, transport and regulatory information, users should refer to the product‑specific Safety Data Sheet (SDS) and local legislation.
