Pyridinium

Pyridinium
Names
	Preferred IUPAC name Pyridin-1-ium
Identifiers
CAS Number	16969-45-2 [PubChem];
3D model (JSmol)	Interactive image;
ChemSpider	4169387 ;
PubChem CID	4989215;
UNII	RNZ2DM8Q8K ;
CompTox Dashboard (EPA)	DTXSID20407294 ;
	InChI InChI=1S/C5H5N/c1-2-4-6-5-3-1/h1-5H/p+1 Key: JUJWROOIHBZHMG-UHFFFAOYSA-O ; InChI=1S/C5H5N/c1-2-4-6-5-3-1/h1-5H/p+1; InChI=1S/C5H5N/c1-2-4-6-5-3-1/h1-5H/p+1 Key: JUJWROOIHBZHMG-UHFFFAOYSA-O;
	SMILES c1cc[nH+]cc1;
Properties
Chemical formula	[C5H5NH]+
Molar mass	80.110 g·mol−1
Acidity (pKa)	~5
Conjugate base	Pyridine
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Pyridinium refers to the cation [C₅H₅NH]⁺. It is the conjugate acid of pyridine. Many related cations are known involving substituted pyridines, e.g. picolines, lutidines, collidines. They are prepared by treating pyridine with acids.

As pyridine is often used as an organic base in chemical reactions, pyridinium salts are produced in many acid-base reactions. Its salts are often insoluble in the organic solvent, so precipitation of the pyridinium leaving group complex is an indication of the progress of the reaction.

Pyridinium cations are aromatic, as determined through Hückel's rule. They are isoelectronic with benzene.