Cyclopentadienyl radical

• Formula: C₅H₅
• Molecular weight: 65.0932
• IUPAC Standard InChI: InChI=1S/C5H5/c1-2-4-5-3-1/h1-5H Copy

  
• IUPAC Standard InChIKey: HPYIUKIBUJFXII-UHFFFAOYSA-N Copy
• CAS Registry Number: 2143-53-5
• Chemical structure:
  This structure is also available as a 2d Mol file or as a computed 3d SD file
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• Information on this page:
  • Gas phase ion energetics data
  • Vibrational and/or electronic energy levels
  • References
  • Notes
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Gas phase ion energetics data

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Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.

Data evaluated as indicated in comments:
HL - Edward P. Hunter and Sharon G. Lias

Data compiled as indicated in comments:
B - John E. Bartmess
LLK - Sharon G. Lias, Rhoda D. Levin, and Sherif A. Kafafi
RDSH - Henry M. Rosenstock, Keith Draxl, Bruce W. Steiner, and John T. Herron

View reactions leading to C₅H₅⁺ (ion structure unspecified)

Electron affinity determinations

Ionization energy determinations

Anion protonation reactions

 +  =

By formula: C₅H₅^- + H⁺ = C₅H₆

Vibrational and/or electronic energy levels

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Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.

Data compiled by: Marilyn E. Jacox

State:   A

State:   X

Additional references: Jacox, 1994, page 385; Jacox, 1998, page 344; Jacox, 2003, page 364; Liebling and McConnell, 1965; DiMauro, Heaven, et al., 1986

Notes

References

Go To: Top, Gas phase ion energetics data, Vibrational and/or electronic energy levels, NIST Free Links, Notes

Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.

Hunter and Lias, 1998
Hunter, E.P.; Lias, S.G., Evaluated Gas Phase Basicities and Proton Affinities of Molecules: An Update, J. Phys. Chem. Ref. Data, 1998, 27, 3, 413-656, https://doi.org/10.1063/1.556018 . [all data]

Bartmess, Scott, et al., 1979
Bartmess, J.E.; Scott, J.A.; McIver, R.T., Jr., The gas phase acidity scale from methanol to phenol, J. Am. Chem. Soc., 1979, 101, 6047. [all data]

Engelking and Lineberger, 1977
Engelking, P.C.; Lineberger, W.C., Laser photoelectron spectrometry of C₅H₅-: A determination of the electron affinity and Jahn-Teller coupling in cyclopentadienyl, J. Chem. Phys., 1977, 67, 1412. [all data]

McDonald, Bianchina, et al., 1991
McDonald, R.N.; Bianchina, E.J.; Tung, C.C., Electron Photodetachment of Cyclopentadienylidene Anion Radical in a Flowing Afterglow Apparatus - EA and ΔH(f)-Degrees of Cyclopentadienylide, J. Am. Chem. Soc., 1991, 113, 19, 7115, https://doi.org/10.1021/ja00019a005 . [all data]

Richardson, Stephenson, et al., 1973
Richardson, J.H.; Stephenson, L.M.; Brauman, J.I., Photodetachment of electrons from large molecular systems: Cyclopentadienide and methylcyclopentadienide ions. An upper limit to the electron affinities of C₅H₅ and CH₃C₅H₄, J. Chem. Phys., 1973, 59, 5068. [all data]

DiDomenico, Harland, et al., 1972
DiDomenico, A.; Harland, P.W.; Franklin, J.L., Negative ion formation and negative ion-molecule reactions in cyclopentadiene, J. Chem. Phys., 1972, 56, 5299. [all data]

Lossing and Traeger, 1975
Lossing, F.P.; Traeger, J.C., Stabilization in cyclopentadienyl, cyclopentenyl, and cyclopentyl cations, J. Am. Chem. Soc., 1975, 97, 1579. [all data]

Schissel, McAdoo, et al., 1968
Schissel, P.; McAdoo, D.J.; Hedaya, E.; McNeil, D.W., Flash vacuum pyrolysis. III. Formation and ionization of cyclopentadienyl, cyclopentadienyl nickel, and dihydrofulvalene (dicyclopentadienyl) derived from nickelocene, J. Chem. Phys., 1968, 49, 5061. [all data]

Harrison, Honnen, et al., 1960
Harrison, A.G.; Honnen, L.R.; Dauben, H.J., Jr.; Lossing, F.P., Free radicals by mass spectrometry. XX. Ionization potentials of cyclopentadienyl and cycloheptatrienyl radicals, J. Am. Chem. Soc., 1960, 82, 5593. [all data]

Cumming and Kebarle, 1978
Cumming, J.B.; Kebarle, P., Summary of gas phase measurements involving acids AH. Entropy changes in proton transfer reactions involving negative ions. Bond dissociation energies D(A-H) and electron affinities EA(A), Can. J. Chem., 1978, 56, 1. [all data]

Thrush, 1956
Thrush, B.A., Spectrum of the Cyclopentadienyl Radical, Nature, 1956, 178, 4525, 155, https://doi.org/10.1038/178155a0 . [all data]

Porter and Ward, 1968
Porter, G.; Ward, B., The Photolytic Preparation of Cyclopentadienyl and Phenyl Nitrene from Benzene Derivatives, Proc. Roy. Soc. (London) A303, 1968, 303, 1473, 139, https://doi.org/10.1098/rspa.1968.0044 . [all data]

Engleman and Ramsay, 1970
Engleman, R., Jr.; Ramsay, D.A., Electronic absorption spectrum of the cyclopentadienyl radical (C, Can. J. Phys., 1970, 48, 8, 964, https://doi.org/10.1139/p70-125 . [all data]

Nelson, Pasternack, et al., 1983
Nelson, H.H.; Pasternack, L.; McDonald, J.R., Excitation and emission spectra of the 2A´´2 «8637» → 2E´´1 system of the gas-phase cyclopentadienyl radical, Chem. Phys., 1983, 74, 2, 227, https://doi.org/10.1016/0301-0104(83)80025-1 . [all data]

Yu, Foster, et al., 1988
Yu, L.; Foster, S.C.; Williamson, J.M.; Heaven, M.C.; Miller, T.A., Rotationally resolved electronic spectrum of jet-cooled cyclopentadienyl radical, J. Phys. Chem., 1988, 92, 15, 4263, https://doi.org/10.1021/j100326a004 . [all data]

Sun and Bernstein, 1995
Sun, S.; Bernstein, E.R., Vibronic structure of the cyclopentadienyl radical and its nonrigid van der Waals cluster with nitrogen, J. Chem. Phys., 1995, 103, 11, 4447, https://doi.org/10.1063/1.470633 . [all data]

Applegate, Bezant, et al., 2001
Applegate, B.E.; Bezant, A.J.; Miller, T.A., The Jahn--Teller and related effects in the cyclopentadienyl radical. II. Vibrational analysis of the A [sup 2]A[sub 2][sup ´´]--X [sup 2]E[sub 1][sup ´´] electronic transition, J. Chem. Phys., 2001, 114, 11, 4869, https://doi.org/10.1063/1.1348276 . [all data]

Yu, Williamson, et al., 1989
Yu, L.; Williamson, J.M.; Miller, T.A., Rotationally resolved electronic spectrum of jet-cooled deuterated cyclopentadienyl radical, Chem. Phys. Lett., 1989, 162, 6, 431, https://doi.org/10.1016/0009-2614(89)87003-4 . [all data]

Korolev and Nefedov, 1993
Korolev, V.A.; Nefedov, O.M., Izv. Akad. Nauk, 1993, Ser. Khim., 1497. [all data]

Jacox, 1994
Jacox, M.E., Vibrational and electronic energy levels of polyatomic transient molecules, American Chemical Society, Washington, DC, 1994, 464. [all data]

Jacox, 1998
Jacox, M.E., Vibrational and electronic energy levels of polyatomic transient molecules: supplement A, J. Phys. Chem. Ref. Data, 1998, 27, 2, 115-393, https://doi.org/10.1063/1.556017 . [all data]

Jacox, 2003
Jacox, M.E., Vibrational and electronic energy levels of polyatomic transient molecules: supplement B, J. Phys. Chem. Ref. Data, 2003, 32, 1, 1-441, https://doi.org/10.1063/1.1497629 . [all data]

Liebling and McConnell, 1965
Liebling, G.R.; McConnell, H.M., Study of Molecular Orbital Degeneracy in C5H5, J. Chem. Phys., 1965, 42, 11, 3931, https://doi.org/10.1063/1.1695862 . [all data]

DiMauro, Heaven, et al., 1986
DiMauro, L.F.; Heaven, M.; Miller, T.A., Lifetimes of the lowest excited states of the cyclopentadienyl and the monomethylcyclopentadienyl radicals, Chem. Phys. Lett., 1986, 124, 6, 489, https://doi.org/10.1016/0009-2614(86)85061-8 . [all data]

Notes

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• Symbols used in this document:
  

  EA	Electron affinity
  ΔrG°	Free energy of reaction at standard conditions
  ΔrH°	Enthalpy of reaction at standard conditions

• Data from NIST Standard Reference Database 69: NIST Chemistry WebBook
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