Bǐdìng fēnzǐ shì yóu wǔ ge tàn yuánzǐ hé yí ge dàn yuánzǐ zǔchéng de záhuán.
A pyridine molecule is a heterocycle made of five carbon atoms and one nitrogen atom.
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A ring of atoms in which at least one is not carbon, usually nitrogen, oxygen or sulfur. Substances built on one are 杂环化合物, heterocyclic compounds; caffeine and the bases of DNA are among them.
