Usually imines refer to compounds with the connectivity R2C=NR, as discussed below. In the older literature, imine refers to the aza analogue of an epoxide. Thus, ethyleneimine is the three-membered ring species C2H4NH.
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. Imines exhibit diverse reactivity and are commonly encountered throughout chemistry. 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 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 is called a primary ketimine; a secondary imine with such groups is called a secondary ketimine.
Aziridine and its derivatives are sometimes referred to as imines.
One way of naming aldimines is to take the name of the radical, remove final "e", and add "-imine", for example ethanimine. Alternately, an imine is named as a derivative of a carbonyl, adding the word "imine" to the name of a carbonyl compound whose oxo group is replaced by an imino group, for example sydnone imine and acetone imine (an intermediate in the synthesis of acetone azine).
N-Sulfinyl imines are a special class of imines having a sulfinyl group attached to the nitrogen atom.
An iminium cation is a related functional group in which the nitrogen has a fourth bond, giving it a positive charge.
An aldimine is an imine that is an analog of an aldehyde.
As such, aldimines have the general formula R-CH=N-R'. Aldimines are similar to ketimines, which are analogs of ketones.
Somewhat like the parent amines, imines are mildly basic and reversibly protonate to give iminium salts. Iminium derivatives are particularly susceptible to reduction to the amines using transfer hydrogenation or by the stoichiometric action of sodium cyanoborohydride. Since imines derived from unsymmetrical ketones are prochiral, their reduction is a useful method for the synthesis of chiral amines.
^Ladenburg, A. (1883) "Ueber die Imine" (About imines), Berichte der Deutschen Chemischen Gesellschaft, 16 : 1149-1152 ; see p. 1150. From p. 1150: "Denn offenbar gehört auch das Piperidin in die Klasse der von mir gesuchten Verbindungen, für welche der Name Imine durch die bestehende Nomenklatur angezeigt ist." (For obviously piperidine also belongs in the class of compounds that are sought by me, for which the name "imines" is indicated by the prevailing nomenclature.)
^Reeves, Jonathan T.; Visco, Michael D.; Marsini, Maurice A.; Grinberg, Nelu; Busacca, Carl A.; Mattson, Anita E.; Senanayake, Chris H. (2015-05-15). "A General Method for Imine Formation Using B(OCH2CF3)3". Organic Letters. 17 (10): 2442-2445. doi:10.1021/acs.orglett.5b00949. ISSN1523-7060. PMID25906082.
^Morales, Sara; Guijarro, Fernando G.; García Ruano, José Luis; Cid, M. Belén (2014-01-22). "A General Aminocatalytic Method for the Synthesis of Aldimines". Journal of the American Chemical Society. 136 (3): 1082-1089. doi:10.1021/ja4111418. ISSN0002-7863. PMID24359453.
^Collados, Juan F.; Toledano, Estefanía; Guijarro, David; Yus, Miguel (2012-07-06). "Microwave-Assisted Solvent-Free Synthesis of Enantiomerically Pure N-(tert-Butylsulfinyl)imines". The Journal of Organic Chemistry. 77 (13): 5744-5750. doi:10.1021/jo300919x. ISSN0022-3263. PMID22694241.
^Mandler, Michael; Truong, Phong; Zavalij, Peter; Doyle, Michael (Jan 14, 2014). "Catalytic Conversion of Diazocarbonyl Compounds to Imines: Applications to the Synthesis of Tetrahydropyrimidines and ?-Lactams". Organic Letters. 16 (3): 740-743. doi:10.1021/ol403427s. PMID24423056.
^Koos, Miroslav; Mosher, Harry S. (1993). "?-Amino-?-trifluoromethyl-phenylacetonitrile: A potential reagent for NMR determination of enantiomeric purity of acids". Tetrahedron. 49 (8): 1541-1546. doi:10.1016/S0040-4020(01)80341-0.
^Moureu, Charles; Mignonac, Georges (1920). "Les Cetimines". Annales de Chimie. 9 (13): 322-359. Retrieved 2014.
^J. Martens: Reduction of Imino Groups (C=N) in (G. Helmchen, R. W. Hoffmann, J. Mulzer, E. Schaumann) Houben-Weyl Stereoselective Synthesis, Workbench Edition E21 Volume 7, S. 4199-4238, Thieme Verlag Stuttgart, 1996, ISBN3-13-106124-3.