Pyridine is a heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one CH group replaced by a nitrogen atom. It is used as a precursor to agrochemicals and pharmaceuticals and is also an important solvent and reagent. It is a colorless liquid with a distinctive, unpleasant fish-like odor. The pyridine ring occurs in many important compounds, including the vitamins nicotinamide and pyridoxal.