Are there compounds that are rings of non-carbon atoms, say a ring of six oxygen atoms, or 5-6 nitrogen atoms with attached hydrogens? Or are these too unstable to exist for long (if at all), like long oxygen chains ($\ce{HO_{n}H}$)?
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1This one’s pretty close ;) – Jan Jun 17 '16 at 17:30
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2Are you looking for a single element around the ring? Otherwise borazine would count: https://en.wikipedia.org/wiki/Borazine – jerepierre Jun 17 '16 at 17:32
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2Sulphur forms many cyclic allotropes, and phosphorous has some as well. – bon Jun 17 '16 at 17:34
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There are many common rings with more than one element in them and no carbons. Single element rings seem harder. – matt_black Jun 17 '16 at 19:22
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Good answers so far. Anyone know anything about rings of Oxygen? It wouldn't be aromatic since there wouldn't be any bonds left over. Right? – Justsalt Jun 17 '16 at 19:44
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You can have oxygen atoms in aromatic rings (furan, pyrilium ion), but making such a ring out of oxygen alone would force it to have too much concentrated positive charge. – Oscar Lanzi Jun 17 '16 at 23:36
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Non-carbon cyclic structures can also be found in 3D; boranes yield several examples of cages, as well as some few-atom metal clusters. – Nicolau Saker Neto Jun 18 '16 at 02:04
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see this:-http://chemistry.stackexchange.com/questions/42612/stability-of-isomers-of-n4o – Nilay Ghosh Jun 18 '16 at 03:22
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It seems there is theoretically an O4 square ring https://en.wikipedia.org/wiki/Tetraoxygen, but it doesn't actually exist. But there is an O8 square block if you squeeze hard enough: https://en.wikipedia.org/wiki/Solid_oxygen#Red_oxygen – Justsalt Jun 21 '16 at 17:24
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Pentazole exists - an $\ce{N5H}$ ring. It is stabilised by aromaticity, with 6 $\pi$-electrons in a cyclic, planar system.
Sulphur forms many allotropes which are rings but these do not contain hydrogen. $\ce{S8}$ and $\ce{S7}$ are the most common.
Phosphorus also forms cyclic allotropes such as white phosphorous, $\ce{P4}$.
DavePhD also mentioned in his answer that a silicon analogue of benzene has been synthesised recently but it is not $\ce{Si6H6}$ because it has other groups attached to some of the silicon atoms.
bon
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Pentazole does not quite exist. I mean, well, it kinda does, but that's not quite the same kind of "exists" as benzene or anything... – Ivan Neretin Jun 17 '16 at 20:03
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I doubt that counting lone pairs in pentazole is good idea here. Also many substituted ones are more stable. – Mithoron Jun 17 '16 at 21:36
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You can also have $S_8$: https://upload.wikimedia.org/wikipedia/commons/thumb/f/f1/Molecular_Sulfur_%28S8%29_V.1.svg/2000px-Molecular_Sulfur_%28S8%29_V.1.svg.png – timaeus222 Jun 18 '16 at 21:06
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See Silicon goes aromatic :
Chemists in the UK have constructed a structural analogue of benzene made from silicon atoms. The molecule is not flat like benzene, but it reveals a new type of aromatic stabilisation.
DavePhD
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See Why isn't the Silicon analogue of Benzene flat? for more details. – Ali Caglayan Jun 17 '16 at 21:39
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Do not forget the trihydrogen cation (https://en.wikipedia.org/wiki/Trihydrogen_cation, https://en.wikipedia.org/wiki/Triatomic_hydrogen). This has been found in the interstellar medium and in hydrogen-rich planetary atmospheres, and is believed to be responsible for the formation of early-generation stars.
Oscar Lanzi
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2The trihydrogen cation is an interesting case. Though you can draw a triangular ring between the nuclei, as far as I understand the highest electron density is actually at the centre of the resulting triangle, so you could think of it more like three atoms joined by a Y-shaped bond than a ring. – Nicolau Saker Neto Jun 18 '16 at 02:00