Cyclopentadienyl anion

Short description: Aromatic ionic species

Cyclopentadienyl anion  |  |

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Names
IUPAC name

Cyclopentadienide

Identifiers

CAS Number

* 12127-83-2

3D model (JSmol)

* Interactive image

ChemSpider |

* 2731064

PubChem CID

* 3490527

InChI

* InChI=1S/C5H5/c1-2-4-5-3-1/h1-5H/q-1

Key: SINKOGOPEQSHQD-UHFFFAOYSA-N

* InChI=1/C5H5/c1-2-4-5-3-1/h1-5H/q-1

Key: SINKOGOPEQSHQD-UHFFFAOYAD

SMILES

* [cH-]1cccc1

Properties

Chemical formula

| [C5H5]− 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

Tracking categories (test):

* PairSizeSet

In chemistry, the cyclopentadienyl anion or cyclopentadienide is an aromatic species with a formula of [C5H5]− and abbreviated as Cp−.[1] It is formed by the deprotonation of cyclopentadiene. The cyclopentadienyl anion is a ligand which binds to a metal in organometallic chemistry.[2]

## Contents

* 1 Resonance and aromaticity
* 2 Ligand
* 3 See also
* 4 References

## Resonance and aromaticity

Resonance structures of the cyclopentadienyl anion

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. Each double bond and lone pair provides 2 π-electrons, which are delocalized into the ring.[3] The cyclopentadienyl anion is a conjugated system because there are alternating π and 𝜎 bonds.[4]

Cyclopentadiene has a pKa of about 16. It is acidic relative to many carbon acids. The enhanced acidity is attributed to stabilization of the conjugate base, cyclopentadienyl anion.

## Ligand

Cyclopentadienyl anions form a variety of cyclopentadienyl complexes.[5]

Metallocene structure where "M" is a metal

## See also

* Cyclopentadienyl radical, [C5H5]•
* Cyclopentadienyl cation, [C5H5]+
* Cyclooctatetraenide anion, [C8H8]2−

## References

1. ↑ "Cyclopentadienide". National Center for Biotechnology Information. https://pubchem.ncbi.nlm.nih.gov/compound/3490527#section=Top. Retrieved 14 April 2016.
2. ↑ Smith, Michael B.; March, Jerry (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience, p. 66, ISBN 978-0-471-72091-1, https://books.google.com/books?id=JDR-nZpojeEC&printsec=frontcover
3. ↑ Paul, Satadal; Goswami, Tamal; Misra, Anirban (2015-10-01). "Noncomparative scaling of aromaticity through electron itinerancy". AIP Advances 5 (10): 107211. doi:10.1063/1.4933191. https://aip.scitation.org/doi/10.1063/1.4933191.
4. ↑ "Delocalised electrons- Definition and Examples of Delocalized electrons with FAQs" (in en). https://byjus.com/chemistry/delocalized-electrons/.
5. ↑ C. Elschenbroich (2006). Organometallics. VCH. ISBN 978-3-527-29390-2.

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*[CID]: Compound ID