Heterocyclic ring
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In chemistry, a heterocyclic ring is a ring-like backbone whose atoms are not all of the same element.

That is, unlike the carbon-only ring like in benzene and napthalene, there are other elements in the backbone, such as in pyrimidine and purine.

The original article can be found at: http://en.wikipedia.org/wiki/Heterocyclic_ring.
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