The key difference between oxo and formyl is that the term oxo refers to an oxygen atom attached to a molecule whereas the term formyl refers to a –CHO group attached to a molecule.
Oxo and formyl are functional groups in organic compounds. Therefore, these are moieties of organic molecules. These functional groups are usually attached to carbon atoms. The chemical and physical properties of organic compounds are determined by these functional groups.
What is Oxo?
The term oxo refers to a functional group that contains a single oxygen atom. Generally, oxo groups can be observed in carbonyl compounds where an oxygen atom binds to a carbon atom through a double bond. This is a functional group, and we can abbreviate it as “=O”.
There are different classes of oxo compounds (carbonyl compounds) such as aldehydes, ketones, carboxylic acids, and amides. In these compounds, oxygen is more electronegative than the carbon atom it is attached to; thus, the oxo group causes these compounds to show resonance. The ability to form resonance structures can affect the reactivity of the molecule. The C=O bond in the oxo group is a polar bond, and the high electronegativity of oxygen atom causes it to attract the bond electrons toward itself, making the carbon atom slightly positively charged. Therefore, the carbon atoms attached to the oxo group becomes an electrophile.
What is Formyl?
Formyl is a functional group having the chemical formula –CHO. This functional group contains a carbonyl centre. When an R group is attached to this functional group, we name it as an aldehyde. The R group can be aliphatic or aromatic; usually, it is an alkyl group. For example, the simplest compound containing a formyl group is formaldehyde. It is an aldehyde compound composed of formyl group attached to a hydrogen atom. The chemical formula of formaldehyde is HCOH.
A formyl group always occurs at the terminus of a molecule. It cannot occur in the middle of a molecule (because one end of the formyl group contains a hydrogen atom which cannot form another bond other than its single bond with the carbonyl carbon atom).
Usually, the formyl group is highly reactive. Therefore, it tends to participate in many reactions. E.g. condensation reactions. Upon the reduction of the formyl group, it forms a primary alcohol. Similarly, upon oxidation, it readily oxidizes to form carboxylic acids.
What is the Difference Between Oxo and Formyl?
The key difference between oxo and formyl is that the term oxo refers to an oxygen atom attached to a molecule whereas the term formyl refers to a –CHO group attached to a molecule. Moreover, an oxo group always occurs in the middle part of the molecule while a formyl group always occurs in the terminus of the molecule.
The following table summarizes the difference between oxo and formyl.
Summary – Oxo vs Formyl
Oxo and formyl are functional groups in organic molecules. The key difference between oxo and formyl is that the term oxo refers to an oxygen atom attached to a molecule whereas the term formyl refers to a –CHO group attached to a molecule.
1. “Chemical Forums: Organic Nomenclature (Why Treat A Group As A Keytone, Not Aldehyde?)”. Chemical Forum, 2020, Available here.