1H-Imidazole

Formula: C₃H₄N₂
Molecular weight: 68.0773
IUPAC Standard InChI: InChI=1S/C3H4N2/c1-2-5-3-4-1/h1-3H,(H,4,5)
IUPAC Standard InChIKey: RAXXELZNTBOGNW-UHFFFAOYSA-N
CAS Registry Number: 288-32-4
Chemical structure:
This structure is also available as a 2d Mol file or as a computed 3d SD file
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Other names: Imidazole; Glyoxalin; Glyoxaline; Imidazol; Imutex; Methanimidamide, N,N'-1,2-ethenediyl-; Miazole; 1,3-Diaza-2,4-cyclopentadiene; 1,3-Diazole; Formamidine, N,N'-vinylene-; Iminazole; IMD; Pyrro(b)monazole; USAF EK-4733; NSC 60522
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Gas phase thermochemistry data

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

Data compiled as indicated in comments:
DRB - Donald R. Burgess, Jr.
ALS - Hussein Y. Afeefy, Joel F. Liebman, and Stephen E. Stein

Quantity	Value	Units	Method	Reference	Comment
Δ_fH°_gas	129.5	kJ/mol	N/A	Zaheeruddin and Lodhi, 1991	Value computed using Δ_fH_solid° value of 60.0 kj/mol from Zaheeruddin and Lodhi, 1991 and Δ_subH° value of 69.5 kj/mol from Jimenez, Roux, et al., 1987.; DRB
Δ_fH°_gas	139.3 ± 1.9	kJ/mol	Cm	Guthrie and Pike, 1987	Heat of hydrolysis; ALS
Δ_fH°_gas	132.9 ± 0.6	kJ/mol	Ccb	Jimenez, Roux, et al., 1987	see Jimenez, Roux, et al., 1986; ALS
Δ_fH°_gas	128. ± 7.5	kJ/mol	Ccb	Bedford, Edmondson, et al., 1962	ALS

Condensed phase thermochemistry data

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

Data compiled as indicated in comments:
ALS - Hussein Y. Afeefy, Joel F. Liebman, and Stephen E. Stein
DH - Eugene S. Domalski and Elizabeth D. Hearing

Quantity	Value	Units	Method	Reference	Comment
Δ_fH°_solid			Ccb	Zaheeruddin and Lodhi, 1991	uncertain value: 59.96 kJ/mol; ALS
Δ_fH°_solid	49.8 ± 0.6	kJ/mol	Ccb	Jimenez, Roux, et al., 1987	see Jimenez, Roux, et al., 1986; ALS
Δ_fH°_solid	58.5 ± 3.3	kJ/mol	Ccb	Bedford, Edmondson, et al., 1962	Reanalyzed by Cox and Pilcher, 1970, Original value = 61. ± 3. kJ/mol; ALS
Quantity	Value	Units	Method	Reference	Comment
Δ_cH°_solid			Ccb	Zaheeruddin and Lodhi, 1991	uncertain value: -1812.17 kJ/mol; ALS
Δ_cH°_solid	-1801.9 ± 0.5	kJ/mol	Ccb	Jimenez, Roux, et al., 1987	see Jimenez, Roux, et al., 1986; ALS
Δ_cH°_solid	-1810.6 ± 3.3	kJ/mol	Ccb	Bedford, Edmondson, et al., 1962	Reanalyzed by Cox and Pilcher, 1970, Original value = -1813.1 ± 3.3 kJ/mol; ALS
Δ_cH°_solid	-1802.	kJ/mol	Ccb	Zimmerman and Geisenfelder, 1961	ALS

Constant pressure heat capacity of solid

C_p,solid (J/mol*K)	Temperature (K)	Reference	Comment
82.4	298.15	Jimenez, Roux, et al., 1987	Cp given as 1.21 J/g*K.; DH
89.78	300.	DeWit, DeKruif, et al., 1983	T = 90 to 370 K.; DH
94.4	310.	DeWit, Offringa, et al., 1983	T = 300 to 450 K.; DH

Reaction thermochemistry data

Go To: Top, Gas phase thermochemistry data, Condensed phase thermochemistry data, References, Notes

Data compiled as indicated in comments:
B - John E. Bartmess
RCD - Robert C. Dunbar
M - Michael M. Meot-Ner (Mautner) and Sharon G. Lias
ALS - Hussein Y. Afeefy, Joel F. Liebman, and Stephen E. Stein

Note: Please consider using the reaction search for this species. This page allows searching of all reactions involving this species. A general reaction search form is also available. Future versions of this site may rely on reaction search pages in place of the enumerated reaction displays seen below.

Individual Reactions

+ = 1H-Imidazole

By formula: C₃H₃N₂^- + H⁺ = C₃H₄N₂

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	1464.1 ± 3.0	kJ/mol	G+TS	Gianola, Ichino, et al., 2005	gas phase; B
Δ_rH°	1465. ± 8.8	kJ/mol	G+TS	Taft, Anvia, et al., 1986	gas phase; value altered from reference due to change in acidity scale; B
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	1433.4 ± 1.7	kJ/mol	IMRE	Gianola, Ichino, et al., 2005	gas phase; B
Δ_rG°	1434. ± 8.4	kJ/mol	IMRE	Taft, Anvia, et al., 1986	gas phase; value altered from reference due to change in acidity scale; B

+ 1H-Imidazole = ( • )

By formula: Na⁺ + C₃H₄N₂ = (Na⁺ • C₃H₄N₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	140. ± 5.0	kJ/mol	CIDT	Huang and Rodgers, 2002	RCD
Δ_rH°	140. ± 5.4	kJ/mol	CIDT	Armentrout and Rodgers, 2000	RCD
Δ_rH°	140. ± 5.0	kJ/mol	CIDT	Rodgers and Armentrout, 1999	RCD

+ 1H-Imidazole = ( • )

By formula: C₃H₃N₂^- + C₃H₄N₂ = (C₃H₃N₂^- • C₃H₄N₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	110.	kJ/mol	PHPMS	Meot-Ner (Mautner), 1988	gas phase; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	123.	J/mol*K	PHPMS	Meot-Ner (Mautner), 1988	gas phase; M

C₃H₄N₂⁺ + 1H-Imidazole = (C₃H₄N₂⁺ • )

By formula: C₃H₄N₂⁺ + C₃H₄N₂ = (C₃H₄N₂⁺ • C₃H₄N₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	99.2	kJ/mol	PHPMS	Meot-Ner (Mautner), 1988	gas phase; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	90.8	J/mol*K	PHPMS	Meot-Ner (Mautner), 1988	gas phase; M

C₄H₁₂N⁺ + 1H-Imidazole = (C₄H₁₂N⁺ • )

By formula: C₄H₁₂N⁺ + C₃H₄N₂ = (C₄H₁₂N⁺ • C₃H₄N₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	94.6	kJ/mol	PHPMS	Meot-Ner (Mautner), 1988	gas phase; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	88.7	J/mol*K	PHPMS	Meot-Ner (Mautner), 1988	gas phase; M

+ 1H-Imidazole = ( • )

By formula: C₂H₃O₂^- + C₃H₄N₂ = (C₂H₃O₂^- • C₃H₄N₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	116.	kJ/mol	PHPMS	Meot-Ner (Mautner), 1988	gas phase; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	102.	J/mol*K	PHPMS	Meot-Ner (Mautner), 1988	gas phase; M

+ = 1H-Imidazole +

By formula: C₅H₆N₂O + H₂O = C₃H₄N₂ + C₂H₄O₂

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-20.2 ± 0.2	kJ/mol	Cm	Wadso, 1960	liquid phase; solvent: Aqueous; Heat of hydrolysis; ALS

+ = + 1H-Imidazole +

By formula: C₉H₁₆N₂O₂ + H₂O = C₄H₈O₂ + C₃H₄N₂ + C₂H₆O

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-44.69 ± 0.67	kJ/mol	Cm	Guthrie and Pike, 1987	liquid phase; Heat of hydrolysis; ALS

+ = 1H-Imidazole + +

By formula: C₁₂H₁₄N₂O₂ + H₂O = C₃H₄N₂ + CH₄O + C₈H₈O₂

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-55.48 ± 0.71	kJ/mol	Cm	Guthrie and Pike, 1987	liquid phase; Heat of hydrolysis; ALS

+ = + 1H-Imidazole +

By formula: C₈H₁₄N₂O₂ + H₂O = C₃H₆O₂ + C₃H₄N₂ + C₂H₆O

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-34.6 ± 1.8	kJ/mol	Cm	Guthrie and Pike, 1987	liquid phase; Heat of hydrolysis; ALS

+ = + 1H-Imidazole

By formula: C₄H₁₁N + C₅H₆N₂O = C₆H₁₃NO + C₃H₄N₂

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-75.6 ± 0.3	kJ/mol	Cm	Wadso, 1962	solid phase; ALS

+ 1H-Imidazole = ( • )

By formula: Li⁺ + C₃H₄N₂ = (Li⁺ • C₃H₄N₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	211. ± 9.6	kJ/mol	CIDT	Huang and Rodgers, 2002	RCD

+ 1H-Imidazole = ( • )

By formula: K⁺ + C₃H₄N₂ = (K⁺ • C₃H₄N₂)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	109. ± 5.4	kJ/mol	CIDT	Huang and Rodgers, 2002	RCD

References

Go To: Top, Gas phase thermochemistry data, Condensed phase thermochemistry data, Reaction thermochemistry data, Notes

Zaheeruddin and Lodhi, 1991
Zaheeruddin, M.; Lodhi, Z.H., Enthalpies of formation of some cyclic compounds, Phys. Chem. (Peshawar Pak.), 1991, 10, 111-118. [all data]

Jimenez, Roux, et al., 1987
Jimenez, P.; Roux, M.V.; Turrion, C., Thermochemical properties of N-heterocyclic compounds. I. Enthalpies of combustion, vapour pressures and enthalpies of sublimation, and enthalpies of formation of pyrazole, imidazole, indazole, and benzimidazole, J. Chem. Thermodyn., 1987, 19, 985-992. [all data]

Guthrie and Pike, 1987
Guthrie, J.P.; Pike, D.C., Hydration of acylimidazoles: tetrahedral intermediates in acylimidazole hydrolysis and nucleophilic attack by imidazole on esters. The question of concerted mechanisms for acyl transfers, Can. J. Chem., 1987, 65, 1951-1969. [all data]

Jimenez, Roux, et al., 1986
Jimenez, P.; Roux, M.V.; Turrion, C.; Gomis, F., Thermochemical properties of some N-heterocyclic compounds, J. Calorim. Anal. Therm. Thermodyn. Chim., 1986, 17, 469-470. [all data]

Bedford, Edmondson, et al., 1962
Bedford, A.F.; Edmondson, P.B.; Mortimer, C.T., Heats of formation and bond energies. Part VI. n-Butyliso-butyraldimine, n-butylisobutylamine, pyrazole, and imidazole, J. Chem. Soc., 1962, 2927-2931. [all data]

Cox and Pilcher, 1970
Cox, J.D.; Pilcher, G., Thermochemistry of Organic and Organometallic Compounds, Academic Press, New York, 1970, 1-636. [all data]

Zimmerman and Geisenfelder, 1961
Zimmerman, H.; Geisenfelder, H., Uber die Mesomerieenergie von Azolen, Z. Electrochem., 1961, 65, 368-371. [all data]

DeWit, DeKruif, et al., 1983
DeWit, H.G.M.; DeKruif, C.G.; Van Miltenburg, J.C., Thermodynamic properties of molecular organic crystals containing organic crystals containing nitrogen, oxygen, and sulfur. II. Molar heat capacities of eight compounds by adiabatic calorimetry, J. Chem. Thermodynam., 1983, 15, 891-902. [all data]

DeWit, Offringa, et al., 1983
DeWit, H.G.M.; Offringa, J.C.A.; De Kruif, C.G.; Van Miltenburg, J.C., Thermodynamic properties of molecular organic crystals containing nitrogen, oxygen and sulfur. III. Molar heat capacities measured by differential scanning calorimetry, Thermochim. Acta, 1983, 65, 43-51. [all data]

Gianola, Ichino, et al., 2005
Gianola, A.J.; Ichino, T.; Hoenigman, R.L.; Kato, S.; Bierbaum, V.M.; Lineberger, W.C., Photoelectron spectra and ion chemistry of imidazolide, J. Phys. Chem. A, 2005, 109, 50, 11504-11514, https://doi.org/10.1021/jp053566o . [all data]

Taft, Anvia, et al., 1986
Taft, R.W.; Anvia, F.; Taagepera, M.; Catalan, J.; Elgueroy, J., Electrostatic proximity effects in the relative basicities of pyrazole, imidazole, pyridazine, and pyrimidine, J. Am. Chem. Soc., 1986, 108, 3237. [all data]

Huang and Rodgers, 2002
Huang, H.; Rodgers, M.T., Sigma versus Pi interactions in alkali metal ion binding to azoles: Threshold collision-induced dissociation and ab initio theory studies, J. Phys. Chem. A, 2002, 106, 16, 4277, https://doi.org/10.1021/jp013630b . [all data]

Armentrout and Rodgers, 2000
Armentrout, P.B.; Rodgers, M.T., An Absolute Sodium Cation Affinity Scale: Threshold Collision-Induced Dissociation Experiments and ab Initio Theory, J. Phys. Chem A, 2000, 104, 11, 2238, https://doi.org/10.1021/jp991716n . [all data]

Rodgers and Armentrout, 1999
Rodgers, M.T.; Armentrout, P.B., Absolute Alkali Metal Ion Binding Affinities of Several Azoles Determined by Threshold Collision-Induced Dissociation, Int. J. Mass Spectrom. Ion Proc., 1999, 185/186/187, 359. [all data]

Meot-Ner (Mautner), 1988
Meot-Ner (Mautner), M., Models for Strong Interactions in Proteins and Enzymes. 2. Interactions of Ions with the Peptide Link and Imidazole, J. Am. Chem. Soc., 1988, 110, 10, 3075, https://doi.org/10.1021/ja00218a014 . [all data]

Wadso, 1960
Wadso, I., Heats of hydrolysis of N-acetylated imidazole, 1,2,4-triazole and tetrazole, Acta Chem. Scand., 1960, 14, 903-908. [all data]

Wadso, 1962
Wadso, I., Heats of aminolysis and hydrolysis of some N-acetyl compounds and of acetic anhydride, Acta Chem. Scand., 1962, 16, 471-478. [all data]

Notes

Go To: Top, Gas phase thermochemistry data, Condensed phase thermochemistry data, Reaction thermochemistry data, References

Symbols used in this document:

C_p,solid	Constant pressure heat capacity of solid
Δ_cH°_solid	Enthalpy of combustion of solid at standard conditions
Δ_fH°_gas	Enthalpy of formation of gas at standard conditions
Δ_fH°_solid	Enthalpy of formation of solid at standard conditions
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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