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In chemistry, a ring is an ambiguous term referring to either a simple cycle of atoms and bonds in a molecule (also called a monocycle or simple ring) or to a connected set of atoms and bonds in which every atom and bond is a member of a cycle (also called a ring system). A ring system that is not a simple ring is called a polycycle or polycyclic ring system. In common usage, the terms ring and ring system are frequently used interchangeably with the appropriate definition often depending upon the context. Typically, the term ring denotes a simple ring, unless otherwise qualified, as for example in terms like "polycyclic ring", "fused ring", "spiro ring" and "indole ring", where clearly a polycyclic ring system is intended. Likewise, the term ring system typically denotes a polycyclic ring system, except in terms like "monocyclic ring system" or "pyridine ring system". To reduce ambiguity, IUPAC's recommendations on organic nomenclature avoid the use of the term "ring" by using phrases such as "monocyclic parent" and "polycyclic ring system". A molecule containing one or more rings is termed a cyclic compound, a molecule containing two or more rings (either in the same or different ring systems) is termed a polycyclic compound and a molecule containing no rings is termed an acyclic or open-chain compound. A recursive definition of a ring system, equivalent to the one given above, is that it is either a simple ring, or the union of two ring systems that share one or more atoms in common. A simple or monocyclic ring contains the same number bonds as the number of atoms, and a polycyclic ring system contains a greater number of bonds than the number of atoms. A homocycle or homocyclic ring is a ring in which all atoms are of the same chemical element. A heterocycle or heterocyclic ring is a ring containing atoms of at least two different elements, i.e. a non-homocyclic ring. A carbocycle or carbocyclic ring is a homocyclic ring in which all of the atoms are carbon. An important class of carbocycles are alicyclic rings, and an important subclass of these are cycloalkanes. ==See also== *Cyclic compound *Polycyclic compound *Heterocyclic compound *Bicyclic molecule *Spiro compound 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ring (chemistry)」の詳細全文を読む スポンサード リンク
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