Hydrogen cyanide

Formula: CHN
Molecular weight: 27.0253
IUPAC Standard InChI: InChI=1S/CHN/c1-2/h1H
IUPAC Standard InChIKey: LELOWRISYMNNSU-UHFFFAOYSA-N
CAS Registry Number: 74-90-8
Chemical structure:
This structure is also available as a 2d Mol file
Other names: Hydrocyanic acid; AC; Blausaeure (German); Carbon hydride nitride (CHN); Formic anammonide; Formonitrile; HCN; Prussic Acid; Cyclon; Acide cyanhydrique; Acido cianidrico; Aero Liquid HCN; Blausaeure; Blauwzuur; Cyaanwaterstof; Cyanwasserstoff; Cyclone B; Cyjanowodor; Evercyn; NA 1051; Prussic acid, unstabilized; Rcra waste number P063; UN 1051; Zaclondiscoids; Carbon hydride nitride; Zootic acid; Agent AC; Nitrilomethane
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Information on this page:
Other data available:
- Gas phase thermochemistry data
- Condensed phase thermochemistry data
- Phase change data
- Reaction thermochemistry data: reactions 1 to 50, reactions 51 to 92
- Henry's Law data
- Ion clustering data
- IR Spectrum
- Mass spectrum (electron ionization)
- Vibrational and/or electronic energy levels
- Gas Chromatography
Data at other public NIST sites:
- Microwave spectra (on physics lab web site)
- Gas Phase Kinetics Database
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Gas phase ion energetics data

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

Data compiled as indicated in comments:
B - John E. Bartmess
LBLHLM - Sharon G. Lias, John E. Bartmess, Joel F. Liebman, John L. Holmes, Rhoda D. Levin, and W. Gary Mallard
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 CHN⁺ (ion structure unspecified)

Quantity	Value	Units	Method	Reference	Comment
IE (evaluated)	13.60 ± 0.01	eV	N/A	N/A	L
Quantity	Value	Units	Method	Reference	Comment
Proton affinity (review)	712.9	kJ/mol	N/A	Hunter and Lias, 1998	HL
Quantity	Value	Units	Method	Reference	Comment
Gas basicity	681.6	kJ/mol	N/A	Hunter and Lias, 1998	HL

Electron affinity determinations

EA (eV)	Method	Reference	Comment
0.00156	N/A	Ard, Garrett, et al., 2009	B
>1.00171	EIAE	Tsuda, Yokohata, et al., 1971	From CH₃CN; G3MP2B3 calculations indicate that the anion is unbound by ca. 1 eV. Possibly C2H3- instead.; B

Ionization energy determinations

IE (eV)	Method	Reference	Comment
13.71	EI	Lageot, 1972	LLK
13.59 ± 0.01	PI	Dibeler and Liston, 1968	RDSH
13.60 ± 0.01	PE	Baker and Turner, 1968	RDSH
13.73 ± 0.09	EI	Varsel, Morrell, et al., 1960	RDSH
13.7 ± 0.1	EI	Kusch, Hustrulid, et al., 1937	RDSH
13.61	PE	Kreile, Schweig, et al., 1982	Vertical value; LBLHLM
13.607 ± 0.002	PE	Fridh and Asbrink, 1975	Vertical value; LLK
13.60	PE	Potts and Williams, 1974	Vertical value; LLK
13.61 ± 0.01	PE	Frost, Lee, et al., 1973	Vertical value; LLK

Appearance energy determinations

Ion	AE (eV)	Other Products	Method	Reference	Comment
C⁺	23.8 ± 0.5	?	EI	Kusch, Hustrulid, et al., 1937	RDSH
CH⁺	21.8 ± 0.5	N	EI	Kusch, Hustrulid, et al., 1937	RDSH
CN⁺	19.43 ± 0.01	H	PI	Berkowitz, Chupka, et al., 1969	RDSH
CN⁺	19.40 ± 0.02	H	PI	Dibeler and Liston, 1968	RDSH
CN⁺	20.1 ± 0.2	H	EI	Kusch, Hustrulid, et al., 1937	RDSH
H⁺	15.18 ± 0.02	CN^-	PI	Berkowitz, Chupka, et al., 1969	RDSH
H⁺	19.00 ± 0.01	CN	PI	Berkowitz, Chupka, et al., 1969	RDSH
NH⁺	24.9 ± 0.5	C	EI	Kusch, Hustrulid, et al., 1937	RDSH
N⁺	25.6 ± 0.5	CH	EI	Kusch, Hustrulid, et al., 1937	RDSH

De-protonation reactions

CN^- + = Hydrogen cyanide

By formula: CN^- + H⁺ = CHN

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	1464. ± 4.2	kJ/mol	CIDT	Akin and Ervin, 2006	gas phase; B
Δ_rH°	1466.5 ± 0.71	kJ/mol	D-EA	Bradforth, Kim, et al., 1993	gas phase; B
Δ_rH°	1469. ± 8.8	kJ/mol	G+TS	Bartmess, Scott, et al., 1979	gas phase; value altered from reference due to change in acidity scale; B
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	1433. ± 4.6	kJ/mol	H-TS	Akin and Ervin, 2006	gas phase; B
Δ_rG°	1435.8 ± 1.1	kJ/mol	H-TS	Bradforth, Kim, et al., 1993	gas phase; B
Δ_rG°	1438. ± 8.4	kJ/mol	IMRE	Bartmess, Scott, et al., 1979	gas phase; value altered from reference due to change in acidity scale; B

References

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

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]

Ard, Garrett, et al., 2009
Ard, S.; Garrett, W.R.; Compton, R.N.; Adamowicz, L.; Stepanian, S.G., Rotational states of dipole-bound anions of hydrogen cyanide., Chem. Phys. Lett., 2009, 473, 4-6, 223, https://doi.org/10.1016/j.cplett.2009.04.007 . [all data]

Tsuda, Yokohata, et al., 1971
Tsuda, S.; Yokohata, A.; Umaba, T., Measurement of negative ions formed by electron impact. VIII. Ionization efficiency curves of negative ions from methyl and ethyl cyanides, Bull. Chem. Soc. Jpn., 1971, 44, 1486. [all data]

Lageot, 1972
Lageot, C., Etude des etats excites de l'ion HCN⁺, J. Chim. Phys. Phys.-Chim. Biol., 1972, 68, 214. [all data]

Dibeler and Liston, 1968
Dibeler, V.H.; Liston, S.K., Mass-spectrometric study of photoionization. IX. Hydrogen cyanide and acetonitrile, J. Chem. Phys., 1968, 48, 4765. [all data]

Baker and Turner, 1968
Baker, C.; Turner, D.W., High resolution molecular photoelectron spectroscopy. III.Acetylenes and azaacetylenes, Proc. Roy. Soc. (London), 1968, A308, 19. [all data]

Varsel, Morrell, et al., 1960
Varsel, C.J.; Morrell, F.A.; Resnik, F.E.; Powell, W.A., Qualitative and quantitative analysis of organic compounds. Use of low-voltage mass spectrometry, Anal. Chem., 1960, 32, 182. [all data]

Kusch, Hustrulid, et al., 1937
Kusch, P.; Hustrulid, A.; Tate, J.T., The dissociation of HCN, C₂H₂, C₂N₂ and C₂H₄ by electron impact, Phys. Rev., 1937, 52, 843. [all data]

Kreile, Schweig, et al., 1982
Kreile, J.; Schweig, A.; Thiel, W., Experimental and theoretical investigation of the photoionization of hydrogen cyanide, Chem. Phys. Lett., 1982, 87, 473. [all data]

Fridh and Asbrink, 1975
Fridh, C.; Asbrink, L., Photoelectron electron impact spectrum of HCN, J. Electron Spectrosc. Relat. Phenom., 1975, 7, 119. [all data]

Potts and Williams, 1974
Potts, A.W.; Williams, T.A., The observation of "forbidden" transitions in He II photoelectron spectra, J. Electron Spectrosc. Relat. Phenom., 1974, 3, 3. [all data]

Frost, Lee, et al., 1973
Frost, D.C.; Lee, S.T.; McDowell, C.A., The photoelectron spectrum of HCP and comments on the first photoelectron band of HCN, Chem. Phys. Lett., 1973, 23, 472. [all data]

Berkowitz, Chupka, et al., 1969
Berkowitz, J.; Chupka, W.A.; Walter, T.A., Photoionization of HCN: the electron affinity and heat of formation of CN, J. Chem. Phys., 1969, 50, 1497. [all data]

Akin and Ervin, 2006
Akin, F.A.; Ervin, K.M., Collision-induced dissociation of HS-(HCN): Unsymmetrical hydrogen bonding in a proton-bound dimer anion, J. Phys. Chem. A, 2006, 110, 4, 1342-1349, https://doi.org/10.1021/jp0540454 . [all data]

Bradforth, Kim, et al., 1993
Bradforth, S.E.; Kim, E.H.; Arnold, D.W.; Neumark, D.M., Photoelectron Spectroscopy of CN-, NCO-, and NCS-, J. Chem. Phys., 1993, 98, 2, 800, https://doi.org/10.1063/1.464244 . [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]

Notes

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

Symbols used in this document:

AE Appearance energy

EA Electron affinity

IE (evaluated) Recommended ionization energy

Δ_rG° Free energy of reaction at standard conditions

Δ_rH° Enthalpy of reaction at standard conditions
Data from NIST Standard Reference Database 69: NIST Chemistry WebBook
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AE	Appearance energy
EA	Electron affinity
IE (evaluated)	Recommended ionization energy
Δ_rG°	Free energy of reaction at standard conditions
Δ_rH°	Enthalpy of reaction at standard conditions