Iminium
= Iminium
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= Iminium ion
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An <iminium> ion contains a positively charged nitrogen associated with a carbon-nitrogen double bond, commonly $\mathrm{R_2C{=}NR_2^+}$. Protonation or alkylation of an imine can produce such a species.
The carbon is electrophilic, supporting nucleophilic addition. Iminium formation therefore provides a way to activate carbonyl-derived substrates through temporary nitrogen-containing intermediates.