1,4-Cyclohexadiene

Formula: C₆H₈
Molecular weight: 80.1277
IUPAC Standard InChI: InChI=1S/C6H8/c1-2-4-6-5-3-1/h1-2,5-6H,3-4H2
IUPAC Standard InChIKey: UVJHQYIOXKWHFD-UHFFFAOYSA-N
CAS Registry Number: 628-41-1
Chemical structure:
This structure is also available as a 2d Mol file or as a computed 3d SD file
The 3d structure may be viewed using Java or Javascript.
Other names: 1,4-Dihydrobenzene; Cyclohexa-1,4-diene
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Condensed phase thermochemistry data

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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°_liquid	66.1 ± 3.1	kJ/mol	Ccb	Luk'yanova, Timofeeva, et al., 1991	ALS
Δ_fH°_liquid	69.70 ± 0.58	kJ/mol	Ccr	Steele, Chirico, et al., 1989	ALS
Quantity	Value	Units	Method	Reference	Comment
Δ_cH°_liquid	-3570.5 ± 3.0	kJ/mol	Ccb	Luk'yanova, Timofeeva, et al., 1991	Corresponding Δ_fHº_liquid = 66.1 kJ/mol (simple calculation by NIST; no Washburn corrections); ALS
Δ_cH°_liquid	-3574.08 ± 0.48	kJ/mol	Ccr	Steele, Chirico, et al., 1989	Corresponding Δ_fHº_liquid = 69.70 kJ/mol (simple calculation by NIST; no Washburn corrections); ALS
Quantity	Value	Units	Method	Reference	Comment
S°_liquid	189.37	J/mol*K	N/A	Geipel and Wolf, 1976	DH

Constant pressure heat capacity of liquid

C_p,liquid (J/mol*K)	Temperature (K)	Reference	Comment
142.2	298.15	Steele, Chirico, et al., 1989	DH
145.94	298.15	Geipel and Wolf, 1976	T = 10 to 300 K.; DH

Reaction thermochemistry data

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Data compiled by: 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

2 + 1,4-Cyclohexadiene =

By formula: 2H₂ + C₆H₈ = C₆H₁₂

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-233.	kJ/mol	Chyd	Roth, Adamczak, et al., 1991	liquid phase
Δ_rH°	-225.5 ± 1.4	kJ/mol	Chyd	Turner, Mallon, et al., 1973	liquid phase; solvent: Glacial acetic acid

= 1,4-Cyclohexadiene

By formula: C₆H₈ = C₆H₈

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-1.6 ± 0.8	kJ/mol	Eqk	Taskinen and Nummelin, 1986	liquid phase; solvent: (CH3)2SO; GLC

Gas phase ion energetics data

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

Data compiled as indicated in comments:
LLK - Sharon G. Lias, Rhoda D. Levin, and Sherif A. Kafafi
RDSH - Henry M. Rosenstock, Keith Draxl, Bruce W. Steiner, and John T. Herron
LBLHLM - Sharon G. Lias, John E. Bartmess, Joel F. Liebman, John L. Holmes, Rhoda D. Levin, and W. Gary Mallard

View reactions leading to C₆H₈⁺ (ion structure unspecified)

Quantity	Value	Units	Method	Reference	Comment
Proton affinity (review)	837.	kJ/mol	N/A	Hunter and Lias, 1998	HL
Quantity	Value	Units	Method	Reference	Comment
Gas basicity	808.0	kJ/mol	N/A	Hunter and Lias, 1998	HL

Ionization energy determinations

IE (eV)	Method	Reference	Comment
8.82	PE	Kimura, Katsumata, et al., 1981	LLK
8.82 ± 0.02	PE	Bieri, Burger, et al., 1977	LLK
8.82 ± 0.02	PI	Demeo and El-Sayed, 1970	RDSH
8.65 ± 0.05	EI	Franklin and Carroll, 1969	RDSH
8.80	PE	Bischof, Hashmall, et al., 1969	RDSH
8.82	PE	Kimura, Katsumata, et al., 1981	Vertical value; LLK
8.82	PE	Bock and Kaim, 1980	Vertical value; LLK
8.80	PE	Kobayashi, 1978	Vertical value; LLK
8.82	PE	Heilbronner, Brogli, et al., 1976	Vertical value; LLK

Appearance energy determinations

Ion	AE (eV)	Other Products	Method	Reference	Comment
C₃H₂⁺	19.21 ± 0.15	?	EI	Franklin and Carroll, 1969	RDSH
C₃H₃⁺	15.20 ± 0.10	?	EI	Franklin and Carroll, 1969	RDSH
C₃H₄⁺	13.95 ± 0.10	?	EI	Franklin and Carroll, 1969	RDSH
C₄H₂⁺	17.82 ± 0.25	C₂H₂⁺²H₂	EI	Franklin and Carroll, 1969	RDSH
C₄H₃⁺	17.08 ± 0.10	C₂H₂+H₂+H?	EI	Franklin and Carroll, 1969	RDSH
C₄H₄⁺	13.55 ± 0.10	C₂H₂+H₂	EI	Franklin and Carroll, 1969	RDSH
C₄H₅⁺	14.48 ± 0.10	C₂H₂+H	EI	Franklin and Carroll, 1969	RDSH
C₄H₆⁺	12.17 ± 0.10	C₂H₂	EI	Franklin and Carroll, 1969	RDSH
C₅H₃⁺	16.12 ± 0.10	CH₃+H₂?	EI	Franklin and Carroll, 1969	RDSH
C₅H₅⁺	13.41 ± 0.10	CH₃	EI	Franklin and Carroll, 1969	RDSH
C₅H₅⁺	13.6	CH₃	EI	Harrison, Haynes, et al., 1965	RDSH
C₆H₅⁺	13.92 ± 0.10	H₂+H	EI	Franklin and Carroll, 1969	RDSH
C₆H₆⁺	9.61 ± 0.10	H₂	EI	Franklin and Carroll, 1969	RDSH
C₆H₆⁺	9.86 ± 0.05	H₂	EI	Franklin and Carroll, 1969	RDSH
C₆H₇⁺	10.55	H	PIPECO	Lias and Ausloos, 1985	LBLHLM
C₆H₇⁺	10.94 ± 0.10	H	EI	Franklin and Carroll, 1969	RDSH

References

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Luk'yanova, Timofeeva, et al., 1991
Luk'yanova, V.A.; Timofeeva, L.P.; Kozina, M.P.; Kirin, V.N.; Tarakanova, A.V., Enthalpies of formation of certain unsaturated cyclic hydrocarbons, Russ. J. Phys. Chem. (Engl. Transl.), 1991, 65, 439-441. [all data]

Steele, Chirico, et al., 1989
Steele, W.V.; Chirico, R.D.; Nguyen, A.; Hossenlopp, I.A.; Smith, N.K., Determination of some pure compound ideal-gas enthalpies of formation, AIChE Symp. Ser., 1989, 85, 140-162. [all data]

Geipel and Wolf, 1976
Geipel, G.; Wolf, G., Die molare Wärmekapazität von Cyclohexadien(1,4) und Cyclohexadien(1,3) im Temperaturegebiet von 10...300K, Z. Phys. Chem., 1976, 257, 587-593. [all data]

Roth, Adamczak, et al., 1991
Roth, W.R.; Adamczak, O.; Breuckmann, R.; Lennartz, H.-W.; Boese, R., Die Berechnung von Resonanzenergien; das MM2ERW-Kraftfeld, Chem. Ber., 1991, 124, 2499-2521. [all data]

Turner, Mallon, et al., 1973
Turner, R.B.; Mallon, B.J.; Tichy, M.; Doering, W.v.E.; Roth, W.R.; Schroder, G., Heats of hydrogenation. X. Conjugative interaction in cyclic dienes and trienes, J. Am. Chem. Soc., 1973, 95, 8605-8610. [all data]

Taskinen and Nummelin, 1986
Taskinen, E.; Nummelin, K., Thermodynamics of vinyl ethers. 31. Isomer equilibria in some six- and seven-membered cyclic dienes, J. Org. Chem., 1986, 50, 4844-4847. [all data]

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]

Kimura, Katsumata, et al., 1981
Kimura, K.; Katsumata, S.; Achiba, Y.; Yamazaki, T.; Iwata, S., Ionization energies, Ab initio assignments, and valence electronic structure for 200 molecules in Handbook of HeI Photoelectron Spectra of Fundamental Organic Compounds, Japan Scientific Soc. Press, Tokyo, 1981. [all data]

Bieri, Burger, et al., 1977
Bieri, G.; Burger, F.; Heilbronner, E.; Maier, J.P., Valence ionization enrgies of hydrocarbons, Helv. Chim. Acta, 1977, 60, 2213. [all data]

Demeo and El-Sayed, 1970
Demeo, D.A.; El-Sayed, M.A., Ionization potential and structure of olefins, J. Chem. Phys., 1970, 52, 2622. [all data]

Franklin and Carroll, 1969
Franklin, J.L.; Carroll, S.R., Effect of molecular structure on ionic decomposition. II. An electron-impact study of 1,3-and 1,4-cyclohexadiene and 1,3,5-hexatriene, J. Am. Chem. Soc., 1969, 91, 6564. [all data]

Bischof, Hashmall, et al., 1969
Bischof, P.; Hashmall, J.A.; Heilbronner, E.; Hornung, V., Photoelektronspektroskopische Bestimmung der Wechselwirkung zwischen nichtkonjugierten Doppelbindungen, Helv. Chim. Acta, 1969, 52, 1745. [all data]

Bock and Kaim, 1980
Bock, H.; Kaim, W., Radical ions. 37. Ionization and one-electron oxidation of electron-rich silylalkyl olefins, J. Am. Chem. Soc., 1980, 102, 4429. [all data]

Kobayashi, 1978
Kobayashi, T., A new rule for photoelectron angular distributions of molecules, Phys. Lett. A, 1978, 69, 31. [all data]

Heilbronner, Brogli, et al., 1976
Heilbronner, E.; Brogli, F.; Vogel, E., Photoelectron spectroscopic assignment of symmetry to the ground state and first excited state of the 1,4-cyclohexadiene radical cation, J. Electron Spectrosc. Relat. Phenom., 1976, 9, 227. [all data]

Harrison, Haynes, et al., 1965
Harrison, A.G.; Haynes, P.; McLean, S.; Meyer, F., The mass spectra of methyl-substituted cyclopentadienes, J. Am. Chem. Soc., 1965, 87, 5099. [all data]

Lias and Ausloos, 1985
Lias, S.G.; Ausloos, P., Structures of C₆H₇⁺ ions formed in unimolecular and bimolecular reactions, J. Chem. Phys., 1985, 82, 3613. [all data]

Notes

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Symbols used in this document:

AE	Appearance energy
C_p,liquid	Constant pressure heat capacity of liquid
S°_liquid	Entropy of liquid at standard conditions
Δ_cH°_liquid	Enthalpy of combustion of liquid at standard conditions
Δ_fH°_liquid	Enthalpy of formation of liquid 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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