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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1$\begingroup$ This one’s pretty close ;) $\endgroup$– JanJun 17, 2016 at 17:30
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2$\begingroup$ Are you looking for a single element around the ring? Otherwise borazine would count: en.wikipedia.org/wiki/Borazine $\endgroup$– jerepierreJun 17, 2016 at 17:32
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2$\begingroup$ Sulphur forms many cyclic allotropes, and phosphorous has some as well. $\endgroup$– bonJun 17, 2016 at 17:34
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$\begingroup$ There are many common rings with more than one element in them and no carbons. Single element rings seem harder. $\endgroup$– matt_blackJun 17, 2016 at 19:22
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$\begingroup$ 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? $\endgroup$– JustsaltJun 17, 2016 at 19:44
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3 Answers
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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.
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$\begingroup$ 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... $\endgroup$ Jun 17, 2016 at 20:03
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$\begingroup$ I doubt that counting lone pairs in pentazole is good idea here. Also many substituted ones are more stable. $\endgroup$– MithoronJun 17, 2016 at 21:36
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1$\begingroup$ Not 10 $\pi$ electrons. Only six, isoelectronic with pyrrhole. $\endgroup$ Jun 17, 2016 at 23:31
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$\begingroup$ You can also have $S_8$: upload.wikimedia.org/wikipedia/commons/thumb/f/f1/… $\endgroup$ Jun 18, 2016 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.
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$\begingroup$ See Why isn't the Silicon analogue of Benzene flat? for more details. $\endgroup$ Jun 17, 2016 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.
answered Jun 17, 2016 at 23:29
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2$\begingroup$ The 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. $\endgroup$ Jun 18, 2016 at 2:00