HCðC anion

Formula: C₂H^-
Molecular weight: 25.0299
CAS Registry Number: 29075-95-4
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Gas phase ion energetics data

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Data compiled by: John E. Bartmess

Protonation reactions

C₂H^- + =

By formula: C₂H^- + H⁺ = C₂H₂

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	379. ± 5.	kcal/mol	AVG	N/A	Average of 8 values; Individual data points
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	370. ± 5.	kcal/mol	AVG	N/A	Average of 7 values; Individual data points

Ion clustering data

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

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Clustering reactions

C₂H^- + = C₃H₂D₅^-

By formula: C₂H^- + CD₄O = C₃H₂D₅^-

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	21.4 ± 1.0	kcal/mol	IMRE	Chabinyc and Brauman, 2000	gas phase; Original dG=11.3 at 350K; dS based on symmetry alone; B
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	12.8 ± 1.0	kcal/mol	IMRE	Chabinyc and Brauman, 2000	gas phase; Original dG=11.3 at 350K; dS based on symmetry alone; B

C₂H^- + = C₃H₂F₃^-

By formula: C₂H^- + CHF₃ = C₃H₂F₃^-

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	19.3 ± 1.0	kcal/mol	IMRE	Chabinyc and Brauman, 2000	gas phase; Original dG=9.2 at 350K; dS based on symmetry alone; B
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	10.7 ± 1.0	kcal/mol	IMRE	Chabinyc and Brauman, 2000	gas phase; Original dG=9.2 at 350K; dS based on symmetry alone; B

C₂H^- + = C₃H₅O^-

By formula: C₂H^- + CH₄O = C₃H₅O^-

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	21.6 ± 2.0	kcal/mol	IMRE	Chabinyc and Brauman, 1999	gas phase; Anchored to MeOH ΔGacid=375.2; B
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	10.90	kcal/mol	IMRE	Mustanir, Matsuoka, et al., 2006	gas phase; B
Δ_rG°	11.6 ± 2.0	kcal/mol	IMRE	Chabinyc and Brauman, 1999	gas phase; Anchored to MeOH ΔGacid=375.2; B

(C₂H^- • 4294967295) + = C₂H^-

By formula: (C₂H^- • 4294967295C₂) + C₂ = C₂H^-

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	162.0 ± 3.8	kcal/mol	N/A	Zhou, Garand, et al., 2007	gas phase; B
Δ_rH°	127.8 ± 3.9	kcal/mol	Ther	Ruscic and Berkowitz, 1990	gas phase; 376.7 0K; corrected with data from Gurvich, Veyts, et al.; B
Δ_rH°	168.0 ± 2.7	kcal/mol	Ther	Bartmess, Scott, et al., 1979	gas phase; value altered from reference due to change in acidity scale; B

C₂H^- + = (C₂H^- • )

By formula: C₂H^- + H₂O = (C₂H^- • H₂O)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	16.2 ± 1.0	kcal/mol	TDAs	Meot-ner, 1988	gas phase; B,M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	18.6	cal/mol*K	PHPMS	Meot-ner, 1988	gas phase; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	10.6 ± 1.0	kcal/mol	TDAs	Meot-ner, 1988	gas phase; B

References

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Chabinyc and Brauman, 2000
Chabinyc, M.L.; Brauman, J.I., Unusual ionic hydrogen bonds: Complexes of acetylides and fluoroform, J. Am. Chem. Soc., 2000, 122, 36, 8739-8745, https://doi.org/10.1021/ja000806z . [all data]

Chabinyc and Brauman, 1999
Chabinyc, M.L.; Brauman, J.I., Hydrogen bond strength and acidity. Structural and energetic correlations for acetylides and alcohols, J. Phys. Chem. A, 1999, 103, 46, 9163-9166, https://doi.org/10.1021/jp992852v . [all data]

Mustanir, Matsuoka, et al., 2006
Mustanir; Matsuoka, M.; Mishima, M.; Koch, H., Stability of complexes of phenylacetylides and benzyl alkoxides with methanol in the gas phase. Acid-base correlation in the ionic hydrogen-bond strength, Bull. Chem. Soc. Japan, 2006, 79, 7, 1118-1125, https://doi.org/10.1246/bcsj.79.1118 . [all data]

Zhou, Garand, et al., 2007
Zhou, J.; Garand, E.; Neumark, D.M., Vibronic structure in C2H and C2D from anion slow electron velocity-map imaging spectroscopy, J. Chem. Phys., 2007, 127, 11, 114313, https://doi.org/10.1063/1.2768932 . [all data]

Ruscic and Berkowitz, 1990
Ruscic, B.; Berkowitz, J., Photoion-pair Formation and Photoelectron-induced Dissociative Attachment in C2H2: D0(HCC-H), J. Chem. Phys., 1990, 93, 8, 5586, https://doi.org/10.1063/1.459629 . [all data]

Gurvich, Veyts, et al.
Gurvich, L.V.; Veyts, I.V.; Alcock, C.B., Hemisphere Publishing, NY, 1989, V. 1 2, Thermodynamic Properties of Individual Substances, 4th Ed. [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]

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]

Notes

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Symbols used in this document:

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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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