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My teacher taught me that in tropylium chloride, the chlorine atom posses negative charge to make the ring aromatic. I wonder that then will this compound will exist in ionic form due to very high polarity or will it exist as covalent molecule only?

Madhav Mittal
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    Tropylium bromide was deduced to be a salt by Doering and Knox in 1954 by analysis of its infrared and ultraviolet spectra. The ionic structures of tropylium perchlorate and tropylium iodide have been confirmed by X-ray crystallography. Wikipedia – Poutnik Jan 16 '24 at 08:37
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    https://scripts.iucr.org/cgi-bin/paper?S0365110X55002053 – Mithoron Jan 16 '24 at 12:06

1 Answers1

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The linked source in Mithoron's comment seems not to give a definitive answer, due to the instability/reactivity of the tropylium chloride/7-chloroheptatriene.

We do know that hydroxy-tropylium ($\text{cyclo-}\ce{C7H6OH^+}$) forms an ionic compound with chloride ion [1]. The hydroxyl group is a pi donor, so this case is not exactly equivalent to a simple tropylium ion ring forming an ionic chloride.

Reference

  1. Jandl C, Pöthig A (2017 Oct 1)."Hydroxytropylium chloride: the first crystal structure of an unfunctionalized hydroxytropylium ion". Acta Crystallogr C Struct Chem. 73(Pt 10):810-813. doi: 10.1107/S2053229617013183. Epub 2017 Sep 27. PMID: 28978788.
Oscar Lanzi
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