cyclopentadienide anion

Formula: C₅H₅^-
Molecular weight: 65.0937
IUPAC Standard InChI: InChI=1S/C5H5/c1-2-4-5-3-1/h1-5H/q-1
IUPAC Standard InChIKey: SINKOGOPEQSHQD-UHFFFAOYSA-N
CAS Registry Number: 12127-83-2
Chemical structure:
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Reaction thermochemistry data

Go To: Top, Gas phase ion energetics data, References, Notes

Data compiled as indicated in comments:
B - John E. Bartmess
M - Michael M. Meot-Ner (Mautner) and Sharon G. Lias

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Individual Reactions

cyclopentadienide anion + =

By formula: C₅H₅^- + H⁺ = C₅H₆

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	1481. ± 9.2	kJ/mol	G+TS	Bartmess, Scott, et al., 1979	gas phase; value altered from reference due to change in acidity scale; B
Δ_rH°	1485. ± 12.	kJ/mol	G+TS	Cumming and Kebarle, 1978	gas phase; B
Δ_rH°	1495. ± 8.4	kJ/mol	D-EA	Engelking and Lineberger, 1977	gas phase; B
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	1455. ± 8.4	kJ/mol	IMRE	Bartmess, Scott, et al., 1979	gas phase; value altered from reference due to change in acidity scale; B
Δ_rG°	1459. ± 8.4	kJ/mol	IMRE	Cumming and Kebarle, 1978	gas phase; B

cyclopentadienide anion + = ( • )

By formula: C₅H₅^- + C₅H₆ = (C₅H₅^- • C₅H₆)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	<36.0	kJ/mol	IMRB	Meot-ner, 1988	gas phase; B,M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	84.	J/mol*K	N/A	Meot-ner, 1988	gas phase; Entropy change calculated or estimated, DG<, Δ_rH<; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	<11. ± 4.2	kJ/mol	IMRB	Meot-ner, 1988	gas phase; B

Free energy of reaction

Δ_rG° (kJ/mol)	T (K)	Method	Reference	Comment
15.	250.	PHPMS	Meot-ner, 1988	gas phase; Entropy change calculated or estimated, DG<, Δ_rH<; M

( cyclopentadienide anion • 2C₂D₃N) + C₂D₃N = ( • 3C₂D₃N)

By formula: (C₅H₅^- • 2C₂D₃N) + C₂D₃N = (C₅H₅^- • 3C₂D₃N)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	42.7	kJ/mol	PHPMS	Meot-ner, 1988	gas phase; Entropy change calculated or estimated, Δ_rH<, CD3CN; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	92.	J/mol*K	N/A	Meot-ner, 1988	gas phase; Entropy change calculated or estimated, Δ_rH<, CD3CN; M

Free energy of reaction

Δ_rG° (kJ/mol)	T (K)	Method	Reference	Comment
21.	232.	PHPMS	Meot-ner, 1988	gas phase; Entropy change calculated or estimated, Δ_rH<, CD3CN; M

cyclopentadienide anion + = ( • )

By formula: C₅H₅^- + H₂O = (C₅H₅^- • H₂O)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	46.0 ± 4.2	kJ/mol	TDAs	Meot-ner, 1988	gas phase; B,M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	67.4	J/mol*K	PHPMS	Meot-ner, 1988	gas phase; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	26. ± 4.2	kJ/mol	TDAs	Meot-ner, 1988	gas phase; B

cyclopentadienide anion + = ( • )

By formula: C₅H₅^- + C₇H₈O = (C₅H₅^- • C₇H₈O)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	80.3 ± 4.2	kJ/mol	TDAs	Meot-ner, 1988	gas phase; B,M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	125.	J/mol*K	PHPMS	Meot-ner, 1988	gas phase; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	43.1 ± 4.2	kJ/mol	TDAs	Meot-ner, 1988	gas phase; B

cyclopentadienide anion + = ( • )

By formula: C₅H₅^- + C₂H₃F₃O = (C₅H₅^- • C₂H₃F₃O)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	86.2 ± 4.2	kJ/mol	TDAs	Meot-ner, 1988	gas phase; B,M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	102.	J/mol*K	PHPMS	Meot-ner, 1988	gas phase; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	55.6 ± 4.2	kJ/mol	TDAs	Meot-ner, 1988	gas phase; B

cyclopentadienide anion + = ( • )

By formula: C₅H₅^- + C₃H₆O = (C₅H₅^- • C₃H₆O)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	56.5 ± 4.2	kJ/mol	TDAs	Meot-ner, 1988	gas phase; B,M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	91.2	J/mol*K	PHPMS	Meot-ner, 1988	gas phase; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	29. ± 4.2	kJ/mol	TDAs	Meot-ner, 1988	gas phase; B

cyclopentadienide anion + = ( • )

By formula: C₅H₅^- + C₄H₁₀O = (C₅H₅^- • C₄H₁₀O)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	71.1 ± 4.2	kJ/mol	TDAs	Meot-ner, 1988	gas phase; B,M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	134.	J/mol*K	PHPMS	Meot-ner, 1988	gas phase; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	31. ± 4.2	kJ/mol	TDAs	Meot-ner, 1988	gas phase; B

( cyclopentadienide anion • C₂D₃N) + C₂D₃N = ( • 2C₂D₃N)

By formula: (C₅H₅^- • C₂D₃N) + C₂D₃N = (C₅H₅^- • 2C₂D₃N)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	54.8	kJ/mol	PHPMS	Meot-ner, 1988	gas phase; CD3CN; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	95.4	J/mol*K	PHPMS	Meot-ner, 1988	gas phase; CD3CN; M

cyclopentadienide anion + = ( • )

By formula: C₅H₅^- + CH₄O = (C₅H₅^- • CH₄O)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	55.2 ± 4.2	kJ/mol	TDAs	Meot-ner, 1988	gas phase; B
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	29. ± 4.2	kJ/mol	TDAs	Meot-ner, 1988	gas phase; B

cyclopentadienide anion + = ( • )

By formula: C₅H₅^- + C₂H₃N = (C₅H₅^- • C₂H₃N)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	64.9 ± 4.2	kJ/mol	TDAs	Meot-ner, 1988	gas phase; B
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	36. ± 4.2	kJ/mol	TDAs	Meot-ner, 1988	gas phase; B

( cyclopentadienide anion • ) + = ( • 2)

By formula: (C₅H₅^- • H₂O) + H₂O = (C₅H₅^- • 2H₂O)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	41.8	kJ/mol	PHPMS	Meot-ner, 1988	gas phase; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	72.8	J/mol*K	PHPMS	Meot-ner, 1988	gas phase; M

( cyclopentadienide anion • ) + = ( • 2)

By formula: (C₅H₅^- • C₃H₆O) + C₃H₆O = (C₅H₅^- • 2C₃H₆O)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	41.	kJ/mol	PHPMS	Meot-ner, 1988	gas phase; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	68.6	J/mol*K	PHPMS	Meot-ner, 1988	gas phase; M

cyclopentadienide anion + C₂D₃N = ( • C₂D₃N)

By formula: C₅H₅^- + C₂D₃N = (C₅H₅^- • C₂D₃N)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	64.9	kJ/mol	PHPMS	Meot-ner, 1988	gas phase; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	95.4	J/mol*K	PHPMS	Meot-ner, 1988	gas phase; M

cyclopentadienide anion + CCoO = C₆H₅CoO^-

By formula: C₅H₅^- + CCoO = C₆H₅CoO^-

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	42.7 ± 3.3	kJ/mol	N/A	Sunderlin and Squires, 1999	gas phase; B

cyclopentadienide anion + = C₅H₅Co^-

By formula: C₅H₅^- + Co = C₅H₅Co^-

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	29.3 ± 2.5	kJ/mol	N/A	Sunderlin and Squires, 1999	gas phase; B

Gas phase ion energetics data

Go To: Top, Reaction thermochemistry data, References, Notes

Data compiled by: John E. Bartmess

Protonation reactions

cyclopentadienide anion + =

By formula: C₅H₅^- + H⁺ = C₅H₆

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	1481. ± 9.2	kJ/mol	G+TS	Bartmess, Scott, et al., 1979	gas phase; value altered from reference due to change in acidity scale
Δ_rH°	1485. ± 12.	kJ/mol	G+TS	Cumming and Kebarle, 1978	gas phase
Δ_rH°	1495. ± 8.4	kJ/mol	D-EA	Engelking and Lineberger, 1977	gas phase
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	1455. ± 8.4	kJ/mol	IMRE	Bartmess, Scott, et al., 1979	gas phase; value altered from reference due to change in acidity scale
Δ_rG°	1459. ± 8.4	kJ/mol	IMRE	Cumming and Kebarle, 1978	gas phase

References

Go To: Top, Reaction thermochemistry data, Gas phase ion energetics data, Notes

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]

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]

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]

Meot-ner, 1988
Meot-ner, M., The Ionic Hydrogen Bond and Solvation. 7. Interaction Energies of Carbanions with Solvent Molecules, J. Am. Chem. Soc., 1988, 110, 12, 3858, https://doi.org/10.1021/ja00220a022 . [all data]

Sunderlin and Squires, 1999
Sunderlin, L.S.; Squires, R.R., Bond strengths in cyclopentadienyl metal carbonyl anions, Int. J. Mass Spectrom., 1999, 183, 149-161, https://doi.org/10.1016/S1387-3806(98)14230-6 . [all data]

Notes

Go To: Top, Reaction thermochemistry data, Gas phase ion energetics data, References

Symbols used in this document:

T Temperature

Δ_rG° Free energy of reaction at standard conditions

Δ_rH° Enthalpy of reaction at standard conditions

Δ_rS° Entropy of reaction at standard conditions
Data from NIST Standard Reference Database 69: NIST Chemistry WebBook
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T	Temperature
Δ_rG°	Free energy of reaction at standard conditions
Δ_rH°	Enthalpy of reaction at standard conditions
Δ_rS°	Entropy of reaction at standard conditions