Imine
Imine
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Imine

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Imine

In organic chemistry, an imine (/ɪˈmn/ or /ˈɪmɪn/) is a functional group or organic compound containing a carbonnitrogen double bond (C=N). The nitrogen atom can be attached to a hydrogen or an organic group (R). The carbon atom has two additional single bonds. Imines are common in synthetic and naturally occurring compounds and they participate in many reactions.

Distinction is sometimes made between aldimines and ketimines, derived from aldehydes and ketones, respectively.

In imines the five core atoms (C2C=NX, ketimine; and C(H)C=NX, aldimine; X = H or C) are coplanar. Planarity results from the sp2-hybridization of the mutually double-bonded carbon and the nitrogen atoms. The C=N distance is 1.29–1.31 Å for nonconjugated imines and 1.35 Å for conjugated imines. By contrast, C−N distances in amines and nitriles are 1.47 and 1.16 Å respectively. Rotation about the C=N bond is slow. Using NMR spectroscopy, both E and Z isomers of aldimines have been detected. Owing to steric effects, the E isomer is favored.

The term "imine" was coined in 1883 by the German chemist Albert Ladenburg.

Usually imines refer to compounds with the general formula R2C=NR, as discussed below. In the older literature, imine refers to the aza-analogue of an epoxide. Thus, ethylenimine is the three-membered ring species aziridine C2H4NH. The relationship of imines to amines having double and single bonds can be correlated with imides and amides, as in succinimide vs acetamide.

Imines are related to ketones and aldehydes by replacement of the oxygen with an NR group. When R = H, the compound is a primary imine, when R is hydrocarbyl, the compound is a secondary imine. If this group is not a hydrogen atom, then the compound can sometimes be referred to as a Schiff base. When R3 is OH, the imine is called an oxime, and when R3 is NH2 the imine is called a hydrazone.

A primary imine in which C is attached to both a hydrocarbyl and a H (derived from an aldehyde) is called a primary aldimine; a secondary imine with such groups is called a secondary aldimine. A primary imine in which C is attached to two hydrocarbyls (derived from a ketone) is called a primary ketimine; a secondary imine with such groups is called a secondary ketimine.

N-Sulfinyl imines are the Schiff amides of sulfinic acids.

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