Why does imidazolium ring contain a positive charge?

[scilearner]

 

Just interested how this positive charge occurs. Thank you

[Horza2002]

If you draw the aromatic ring with double bonds instead, you will find one of the nitrogens as 4 bonds around it...its lone pair has acted as a nucleophile and been alkyalted in this case. However, this positive charge can be delocalised onto every position within the ring (try drawing the curly arrows) and so overal, the ring has a poisitve charge that is spread out over it entirly. Thats what the positive charge means

[UC]

Here's a "snapshot" of one of the resonance forms of the ion. As you can see, there is a quaternary nitrogen present. If you use Huckel's rule, I believe that you will find this is an aromatic ring, and the positive charge is delocalized for that reason.

 

[Horza2002]

yer the image provided by UC is what I was trying to explain...picture paints a thousand words!