Cyclopentadienyl anion

In chemistry, the cyclopentadienyl anion or cyclopentadienide is an aromatic species with a formula of [C
5H
5]−
 and abbreviated as Cp−.[1] It is formed from the deprotonation of the molecule cyclopentadiene.

Cyclopentadienyl anion
Identifiers
3D model (JSmol)
ChemSpider
Properties
[C
5H
5]−
 or Cp−
Molar mass 65.09 g/mol
Conjugate acid Cyclopentadiene
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Properties

The cyclopentadienyl anion is a planar, cyclic, regular-pentagonal ion; it has 6 π-electrons (4n + 2, where n = 1), which fulfills Hückel's rule of aromaticity.

The structure shown is a composite of five resonance contributors in which each carbon atom carries part of the negative charge.

Salts of the cyclopentadienyl anion can be stable, e.g., sodium cyclopentadienide. It can also coordinate as a ligand to metal atoms, forming coordination compounds known as cyclopentadienyl complexes. Biscyclopentadienyl complexes are called metallocenes.

Cyclopentadienyl, [C
5H
5]−
, and cyclopentadiene, C
5H
6, can substitute one or more hydrogens, forming derivatives having covalent bonds. (See Cyclopentadiene#Derivatives)

Abbreviation

The abbreviation Cp for cyclopentadienyl played a role in the naming of element 112, copernicium, for which the originally proposed symbol was Cp. However, as Cp− was already in use as the abbreviation for cyclopentadienyl (and Cp had been used for cassiopeium, a former name of lutetium), the symbol for copernicium was changed to Cn.[2]

See also

References
  1. "Cyclopentadienide". PubChem Compound Database. National Center for Biotechnology Information. Retrieved 14 April 2016.
  2. "Copernicium Video – The Periodic Table of Videos – University of Nottingham". Retrieved 2011-02-22.


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