Nomenclature
The systematic name of pyridine, within the Hantzsch–Widman nomenclature recommended by the IUPAC, is azine. However, systematic names for simple compounds are used very rarely, instead heterocyclic nomenclature follows historically established common names. IUPAC discourages the use of azine in favor of pyridine. The numbering of the ring atoms in pyridine starts at the nitrogen (see infobox). An allocation of positions by letter of the Greek alphabet (α-γ) and the substitution pattern nomenclature common for homoaromatic systems (ortho, meta, para) are used sometimes. Here α (ortho), β (meta) and γ (para) refer to the 2, 3 and 4 position, respectively. The systematic name for the pyridine derivatives is pyridinyl, wherein the position of the substituted atom is preceded by a number. However, here again the historical name pyridyl is encouraged by the IUPAC and used instead of the systematic name. The cationic derivative formed by the addition of an electrophile to the nitrogen atom is called pyridinium.
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4-bromopyridine
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2,2′-bipyridine
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pyridine-2,6-dicarboxylic acid (dipicolinic acid)
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General form of the pyridinium cation
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