Editing Heterocyclic compound (section)

== Classification ==
The study of organic heterocyclic chemistry focuses especially on organic unsaturated derivatives, and the preponderance of work and applications involves unstrained organic 5- and 6-membered rings.  Included are [[pyridine]], [[thiophene]], [[pyrrole]], and [[furan]].  Another large class of organic heterocycles refers to those fused to [[benzene ring]]s. For example, the fused benzene derivatives of pyridine, thiophene, pyrrole, and furan are [[quinoline]], [[benzothiophene]], [[indole]], and [[benzofuran]], respectively.  The fusion of two benzene rings gives rise to a third large family of organic compounds. Analogs of the previously mentioned heterocycles for this third family of compounds are [[acridine]], [[dibenzothiophene]], [[carbazole]], and [[dibenzofuran]], respectively.  

Heterocyclic organic compounds can be usefully classified based on their electronic structure. The saturated organic heterocycles behave like the acyclic derivatives. Thus, [[piperidine]] and [[tetrahydrofuran]] are conventional [[amines]] and [[ethers]], with modified steric profiles. Therefore, the study of organic heterocyclic chemistry focuses on organic unsaturated rings.

===Inorganic rings===
Some heterocycles contain no carbon. Examples are [[borazine]] (B<sub>3</sub>N<sub>3</sub> ring), [[phosphazene]] (P<sub>3</sub>N<sub>3</sub> ring), and [[tetrasulfur tetranitride]] (S<sub>4</sub>N<sub>4</sub> ring). In comparison with organic heterocycles, which have numerous commercial applications, inorganic ring systems are mainly of theoretical interest. [[International Union of Pure and Applied Chemistry|IUPAC]] recommends the [[Hantzsch-Widman nomenclature]] for naming heterocyclic compounds.<ref>{{GoldBookRef|title=Hantzsch–Widman name|file=H02737}}</ref>