Tropylium cation

Tropylium
	; skeletal formula
ball-and-stick model	space-filling model
Names
	Preferred IUPAC name Cycloheptatrienylium
	Other names cyc-C; 7H+; 7, Cyclohepta-2,4,6-trienylium, Cyclohepta-1,3,5-triene, 2,4,6-Cycloheptatrienylium
Identifiers
CAS Number	4118-59-6;
3D model (JSmol)	Interactive image;
Beilstein Reference	1902352
ChemSpider	4394444 ;
PubChem CID	5224206 ;
	InChI InChI=1S/C7H7/c1-2-4-6-7-5-3-1/h1-7H/q+1 Key: OJOSABWCUVCSTQ-UHFFFAOYSA-N; : InChI=1S/C7H7/c1-2-4-6-7-5-3-1/h1-7H/q+1 Key: OJOSABWCUVCSTQ-UHFFFAOYSA-N;
	SMILES c1=cc=c[cH+]c=c1;
Properties
Chemical formula	C; 7H+; 7
Molar mass	91.132 g·mol−1
Structure
Point group	D7h
Molecular shape	regular heptagon
Related compounds
Other anions	Tropylium tetrafluoroborate
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

The tropylium ion or cycloheptatrienyl cation is an aromatic species with a formula of [C₇H₇]⁺. Its name derives from the molecule tropine from which cycloheptatriene (tropylidene) was first synthesized in 1881. Salts of the tropylium cation can be stable, even with nucleophiles of moderate strength e.g., tropylium tetrafluoroborate and tropylium bromide (see below). Its bromide and chloride salts can be made from cycloheptatriene and bromine or phosphorus pentachloride, respectively.

It is a regular heptagonal, planar, cyclic ion. It has 6 π-electrons (4n + 2, where n = 1), which fulfills Hückel's rule of aromaticity. It can coordinate as a ligand to metal atoms. The structure shown is a composite of seven resonance contributors in which each carbon atom carries part of the positive charge.

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