The key difference between imine and Schiff base is that an imine is an organic molecule containing a carbon-nitrogen double bond with three alkyl or aryl groups attached to it. Meanwhile, Schiff base is a sub-class of imine containing carbon-nitrogen double bond attached with only alkyl or aryl groups (no hydrogen atom attached).
Imines are organic compounds containing a C=N double bond. Here, the carbon atom is attached to two other groups that are either alkyl/aryl groups or hydrogen atoms. The nitrogen atom is also attached to either alkyl or aryl group.
CONTENTS
1. Overview and Key Difference
2. What is Imine
3. What is Schiff Base
4. Side by Side Comparison – Imine vs Schiff Base in Tabular Form
5. Summary
What is Imine?
The imine is an organic compound containing a C=N functional group. Since one carbon atom can form four covalent bonds, this carbon atom can form two other covalent bonds with other substituents. These substituents are alkyl groups, aryl groups or a hydrogen atom and an alkyl/aryl group. A nitrogen atom can form three covalent bonds. Therefore, the nitrogen atom in the imine can form another covalent bond with another substituent. This substituent can be a hydrogen atom or an alkyl/aryl group. The general structure of an imine is as follows:
Figure 01: General Structure of the Imine Functional 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. Here, 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.
When considering the preparation of imines, the usual method 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. Also, we can use some other methods such as condensation of carbon acids in the presence of nitroso compounds, dehydration of hemiaminals, etc.
What is Schiff Base?
Schiff base is a type of imine which has only alkyl or aryl groups attached to the carbon and nitrogen atoms. Therefore, there are no hydrogen atoms attached to the carbon and nitrogen atoms of the imine functional group.
Generally, these compounds resemble secondary ketimines or secondary aldimines. These are very useful as ligands that involve in the formation of coordinate complexes. We can prepare Schiff bases from aliphatic or aromatic amines in the presence of a carbonyl group via nucleophilic addition reactions.
What is the Difference Between Imine and Schiff Base?
Imines are organic compounds containing a C=N bond. There are two other groups (alkyl, aryl or hydrogen) attached to the carbon atom and the nitrogen atom has one alkyl or aryl group attached to it. Schiff base is a type of imine. Therefore, the key difference between imine and Schiff base is that an imine is an organic molecule containing a carbon-nitrogen double bond which has three alkyl or aryl groups attached to it, whereas Schiff base is a sub-class of imine containing carbon-nitrogen double bond attached with only alkyl or aryl groups (no hydrogen atom attached).
Below infographic shows more detailed comparisons related to the difference between imine and Schiff base.
Summary – Imine vs Schiff Base
Imines are organic compounds containing a C=N bond. There are two other groups (alkyl, aryl or hydrogen) attached to the carbon atom and the nitrogen atom has one alkyl or aryl group attached to it. Schiff base is a type of imine. Therefore, the key difference between imine and Schiff base is that an imine is an organic molecule containing a carbon-nitrogen double bond which has three alkyl or aryl groups attached to it whereas Schiff base is a sub-class of imine containing carbon-nitrogen double bond attached with only alkyl or aryl groups (no hydrogen atom attached).
Reference:
1. Helmenstine, Anne Marie. “Functional Groups in Organic Chemistry.” ThoughtCo, Nov. 5, 2019, Available here.
Image Courtesy:
1. “Imine general structure B” By Hbf878 – Own work (CC0) via Commons Wikimedia
2. “Imino Group V.1” By Jü – Own work (Public Domain) via Commons Wikimedia