Aromatic ionic species
Cyclopentadienyl anion
Names
IUPAC name
Cyclopentadienide
Identifiers
ChemSpider
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
Properties
[C5 H5 ]− 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).
Chemical compound
In chemistry , the cyclopentadienyl anion or cyclopentadienide is an aromatic species with a formula of [C5 H5 ]− 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]
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 .[citation needed ]
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 .[4]
Metallocene structure where "M" is a metal
See also
References
^ "Cyclopentadienide" . PubChem Compound Database . National Center for Biotechnology Information. Retrieved 14 April 2016 .
^ 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
^ 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 .
^ C. Elschenbroich (2006). Organometallics . VCH. ISBN 978-3-527-29390-2 .