Editing Imidazole (section)

==Structure and properties==
Imidazole is a planar 5-membered ring, that exists in two equivalent [[tautomer]]ic forms because hydrogen can be bound to one or another [[nitrogen]] atom. Imidazole is a highly polar compound, as evidenced by its [[electric dipole moment]] of 3.67&nbsp;[[debye|D]],<ref>{{cite journal|last1=Christen|first1=Dines|last2=Griffiths|first2=John H.|last3=Sheridan|first3=John|date=1981|title=The Microwave Spectrum of Imidazole; Complete Structure and the Electron Distribution from Nuclear Quadrupole Coupling Tensors and Dipole Moment Orientation|journal=Zeitschrift für Naturforschung A|volume=36|issue=12|pages=1378–1385|doi=10.1515/zna-1981-1220|bibcode=1981ZNatA..36.1378C|s2cid=3522351|doi-access=free}}</ref> and is highly soluble in water. The compound is classified as [[aromaticity|aromatic]] due to the presence of a planar ring containing 6 [[pi bond|π-electron]]s (a pair of electrons from the protonated nitrogen atom and one from each of the remaining four atoms of the ring). Some [[resonance (chemistry)|resonance]] structures of imidazole are shown below:
:[[File:Resonance-imidazole.svg|none|467x467px]]
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===Amphoterism===
Imidazole is [[amphoteric]], which is to say that it can function both as an acid and as a base. As an acid, the [[Dissociation constant#Acid–base reactions|p''K''<sub>a</sub>]] of imidazole is 14.5, making it less acidic than carboxylic acids, phenols, and imides, but slightly more acidic than alcohols. The acidic proton is the one bound to nitrogen. Deprotonation gives the imidazolide anion, which is symmetrical. As a base, the p''K''<sub>a</sub> of the conjugate acid (cited as p''K''<sub>BH<sup>+</sup></sub> to avoid confusion between the two) is approximately 7, making imidazole approximately sixty times more basic than [[pyridine]]. The basic site is the nitrogen with the lone pair (and not bound to hydrogen). Protonation gives the imidazolium cation, which is symmetrical.