Iminium cations adopt
alkene-like geometries: the central C=N unit is nearly coplanar with all four substituents. Unsymmetrical iminium cations can exist as cis and trans isomers. The C=N bonds, which are near 129 picometers in length, are shorter than C-N single bonds. Cis/trans isomers are observed. The C=N distance is slightly shorter in iminium cations than in the parent imine, and computational studies indicate that the C=N bonding is also stronger in iminium vs imine, although the C=N distance contracts only slightly. These results indicate that the barrier for rotation is higher than in the parent imines.[3][4]
Iminium derivatives are common in biology.
Pyridoxal phosphate reacts with amino acids to give iminium derivatives. Many iminium salts are encountered in synthetic organic chemistry.
Reactions
Iminium salts hydrolyse to give the corresponding ketone or aldehyde:[8]
Unsymmetrical iminium cations undergo cis-trans isomerization. The isomerization is catalyzed by nucleophiles, which add to the unsaturated carbon, breaking the C=N double bond.[3]
^
abJohnson, James E.; Morales, Nora M.; Gorczyca, Andrea M.; Dolliver, Debra D.; McAllister, Michael A. (2001). "Mechanisms of Acid-Catalyzed Z/E Isomerization of Imines". The Journal of Organic Chemistry. 66 (24): 7979–7985.
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10.1021/jo010067k.
PMID11722194.
^Wang, Youliang; Poirier, Raymond A. (1997). "Factors That Influence the CN Stretching Frequency in Imines". The Journal of Physical Chemistry A. 101 (5): 907–912.
Bibcode:
1997JPCA..101..907W.
doi:
10.1021/jp9617332.
^Erkkilä, Anniinä; Majander, Inkeri; Pihko, Petri M. (2007). "Iminium Catalysis". Chem. Rev. 107 (12): 5416–70.
doi:
10.1021/cr068388p.
PMID18072802.
^E. F. Kleinman (2004). "Dimethylmethyleneammonium Iodide and Chloride". Encyclopedia of Reagents for Organic Synthesis. New York: J. Wiley & Sons.
doi:
10.1002/047084289X.rd346.
^C. Schmit; J. B. Falmagne; J. Escudero; H. Vanlierde; L. Ghosez (1990). "A General Synthesis of Cyclobutanones from Olefins and Tertiary Amides: 3-Hexylcyclobutanone". Org. Synth. 69: 199.
doi:
10.15227/orgsyn.069.0199.