tropylium ions 

https://doi.org/10.1351/goldbook.T06523
The delocalized carbenium ion, cycloheptatrienylium, C7H7+, derived formally by detachment of one hydride ion from the CH2 group of cyclohepta-1,3,5-triene and substitution derivatives thereof.
Source:
PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1373 [Terms] [Paper]
Citation: 'tropylium ions' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.T06523 RIS BibTex EndNote
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Last revised: February 24, 2014