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I have come across 6-element rings, 5-element rings, but very rarely 3,4, or 7,8, etc. -element rings. I am not sure of the reason for the rarity of other rings than 5 or 6. Is it just what I have encountered so far do not include non-5/6 rings a whole lot, or is it because of some reasons that there just are not that many non-5/6 rings around?

Edit: The rings I am referring to include both same-element (e.g. benzene, octasulfur, etc.) and different-element (e.g. glucose, fructose, etc.) ones.

Tri Le
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Rings are known in all sorts of sizes. It's just that five- and six-atom rings are most stable under Earthly conditions. Things are different "out there", as in three-membered ring species appearing in interstellar space (http://iopscience.iop.org/article/10.1086/501121/meta) and in the atmosphere of Saturn's moon Titan (http://www.sciencedirect.com/science/article/pii/S0032063313001864). Might such species be precursors to some of the organic compounds we know and love here?

Oscar Lanzi
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