The key difference between imine and enamine is that imine molecule has a C=N bond whereas enamine molecule has a C-N bond.
Imine and enamine molecules are organic compounds containing nitrogen and carbon atoms bonded to each other along with hydrogen atoms or hydrocarbyl groups attached to the carbon and nitrogen atom. These two molecules differ from each other chemically depending on the chemical bond between carbon and nitrogen atom.
What is Imine?
Imines are organic compounds consisting of a C=N functional group. The carbon atom in this functional group can form two other covalent bonds with other substituents (because a carbon atom can form four covalent chemical bonds). These substituents are alkyl groups, aryl groups or a hydrogen atom and an alkyl/aryl group. Since a nitrogen atom can form three covalent bonds, the nitrogen atom in the imine functional group can form another covalent bond with another substituent. This substituent can be a hydrogen atom or an alkyl/aryl group.
The term imine was introduced by the scientist Albert Ladenburg. If the oxygen atom of an aldehyde or a ketone is replaced by an N-R group (where N is a nitrogen atom, and R is an alkyl/aryl group), the compound we get is either an aldimine or a ketimine. In these molecules, if the R group is a hydrogen atom, then we can name the compound as a primary aldimine or primary ketamine. However, if the R group is a hydrocarbyl group, then the compound is a secondary structure.
Usually, the method we use to prepare an imine is the condensation of primary amines or aldehydes. Ketones are used less commonly for this preparation. The synthesis of an imine occurs via nucleophilic addition. Further, we can use some other methods such as condensation of carbon acids in the presence of nitroso compounds, dehydration of hemiaminals, etc.
What is Enamine?
Enamines are organic compounds consisting of an amine group adjacent to a C=C double bond. An enamine is formed from the condensation of an aldehyde or ketone with a secondary amine. These molecules are considered as nitrogen analogues of enols.
Enamines react in a similar way to that of enolate anions. When compared to enols and enolates, the nucleophilic reactivity of enamines is moderate to that of enols and enolates. This moderate nucleophilicity of enamines is a result of the low electronegativity of nitrogen atom compared to the oxygen atom in enols and enolates. However, the reactivity of enamines is different from each other based on the alkyl group attached to the molecule.
What is the Difference Between Imine and Enamine?
Imine and enamine are nitrogen-containing organic compounds. Imines are organic compounds consisting of a C=N functional group while enamines are organic compounds consisting of an amine group adjacent to a C=C double bond. The key difference between imine and enamine is that imine molecule has a C=N bond whereas enamine molecule has a C-N bond.
The following infographic lists the differences between imine and enamine in tabular form.
Summary – Imine vs Enamine
Imine and enamine molecules differ from each other chemically depending on the chemical bond between carbon and nitrogen atom. The key difference between imine and enamine is that imine molecule has C=N bond whereas enamine molecule has C-N bond.
1. “19.8: Nucleophilic Addition of Amines: Imine and Enamine Formation.” Chemistry LibreTexts, Libretexts, 13 Jan. 2021, Available here.