Isobutane

Formula: C₄H₁₀
Molecular weight: 58.1222
IUPAC Standard InChI: InChI=1S/C4H10/c1-4(2)3/h4H,1-3H3
IUPAC Standard InChIKey: NNPPMTNAJDCUHE-UHFFFAOYSA-N
CAS Registry Number: 75-28-5
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: Propane, 2-methyl-; Trimethylmethane; 1,1-Dimethylethane; 2-Methylpropane; iso-C4H10; i-Butane; UN 1969; R 600a; tert-Butane; A 31; Methylpropane; A 31 (hydrocarbon)
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Gas phase thermochemistry data

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

Data compiled as indicated in comments:
ALS - Hussein Y. Afeefy, Joel F. Liebman, and Stephen E. Stein
GT - Glushko Thermocenter, Russian Academy of Sciences, Moscow

Quantity	Value	Units	Method	Reference	Comment
Δ_fH°_gas	-134.2 ± 0.63	kJ/mol	Ccb	Pittam and Pilcher, 1972	ALS
Δ_fH°_gas	-135.6 ± 0.54	kJ/mol	Cm	Prosen, Maron, et al., 1951	see Prosen and Rossini, 1945, Rossini, 1935; ALS
Quantity	Value	Units	Method	Reference	Comment
Δ_cH°_gas	-2869.0 ± 0.59	kJ/mol	Ccb	Pittam and Pilcher, 1972	Corresponding Δ_fHº_gas = -134.2 kJ/mol (simple calculation by NIST; no Washburn corrections); ALS
Δ_cH°_gas	-2867.6 ± 0.46	kJ/mol	Cm	Prosen, Maron, et al., 1951	see Prosen and Rossini, 1945, Rossini, 1935; Corresponding Δ_fHº_gas = -135.6 kJ/mol (simple calculation by NIST; no Washburn corrections); ALS

Constant pressure heat capacity of gas

C_p,gas (J/mol*K)	Temperature (K)	Reference	Comment
34.81	50.	Chen S.S., 1975	Recommended values are in good agreement with those calculated by [ Pitzer K.S., 1946].; GT
47.28	100.
60.29	150.
71.84	200.
89.91	273.15
96.65	298.15
97.15	300.
124.43	400.
149.24	500.
170.37	600.
188.28	700.
203.64	800.
216.94	900.
228.45	1000.
238.49	1100.
247.15	1200.
254.72	1300.
261.29	1400.
267.02	1500.

Constant pressure heat capacity of gas

C_p,gas (J/mol*K)	Temperature (K)	Reference	Comment
82.30 ± 0.06	243.15	Ernst G., 1970	Other experimental values of heat capacity [ Sage B.H., 1937, Sage B.H., 1938] are less accurate, see [ Chen S.S., 1975]. Please also see Dailey B.P., 1943, Wacker P.F., 1947.; GT
89.97 ± 0.06	273.15
95.21 ± 0.10	293.15
100.67 ± 0.10	313.15
106.37 ± 0.11	333.15
109.66	347.6
111.74 ± 0.11	353.15
112.55	359.4
119.62	387.5
137.03	452.5
152.93	520.9
161.29	561.7
169.70	605.3
185.18	692.7

Condensed phase thermochemistry data

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Data compiled by: Eugene S. Domalski and Elizabeth D. Hearing

Quantity	Value	Units	Method	Reference	Comment
S°_liquid	200.79	J/mol*K	N/A	Aston, Kennedy, et al., 1940
S°_liquid	198.7	J/mol*K	N/A	Parks, Shomate, et al., 1937	Extrapolation below 67 K, 44.02 J/mol*K.

Constant pressure heat capacity of liquid

C_p,liquid (J/mol*K)	Temperature (K)	Reference	Comment
129.70	260.	Aston, Kennedy, et al., 1940	T = 20 to 260 K.
128.4	258.3	Parks, Shomate, et al., 1937	T = 79 to 261 K. Value is unsmoothed experimental datum.

Gas phase ion energetics data

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

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
LL - Sharon G. Lias and Joel F. Liebman
LLK - Sharon G. Lias, Rhoda D. Levin, and Sherif A. Kafafi
RDSH - Henry M. Rosenstock, Keith Draxl, Bruce W. Steiner, and John T. Herron

Quantity	Value	Units	Method	Reference	Comment
IE (evaluated)	10.68 ± 0.11	eV	N/A	N/A	L
Quantity	Value	Units	Method	Reference	Comment
Proton affinity (review)	677.8	kJ/mol	N/A	Hunter and Lias, 1998	HL
Quantity	Value	Units	Method	Reference	Comment
Gas basicity	671.3	kJ/mol	N/A	Hunter and Lias, 1998	HL

Ionization energy determinations

IE (eV)	Method	Reference	Comment
10.57	EST	Luo and Pacey, 1992	LL
10.74 ± 0.05	EI	Flesch and Svec, 1973	LLK
10.69	PI	Dewar and Worley, 1969	RDSH
10.79	PI	Turner and Al-Joboury, 1964	RDSH
10.78	PI	Al-Joboury and Turner, 1964	RDSH
10.57	PI	Watanabe, Nakayama, et al., 1962	RDSH
~10.5	PI	Steiner, Giese, et al., 1961	RDSH
11.13	PE	Kimura, Katsumata, et al., 1981	Vertical value; LLK
11.0 ± 0.1	PE	Bieri, Burger, et al., 1977	Vertical value; LLK
11.4	PE	Murrell and Schmidt, 1972	Vertical value; LLK

Appearance energy determinations

Ion	AE (eV)	Other Products	Method	Reference	Comment
CH₃⁺	29.4 ± 0.2	?	EI	Olmsted, Street, et al., 1964	RDSH
C₂H₅⁺	13.80	C₂H₅	EI	Omura, 1961	RDSH
C₃H₅⁺	14.55	?	EI	Omura, 1961	RDSH
C₃H₆⁺	10.89 ± 0.02	CH₄	PI	Mead, Donchi, et al., 1980	LLK
C₃H₆⁺	10.91	CH₄	EI	Wolkoff and Holmes, 1978	LLK
C₃H₆⁺	10.93 ± 0.03	CH₄	PI	Steiner, Giese, et al., 1961	RDSH
C₃H₇⁺	11.16 ± 0.02	CH₃	PI	Mead, Donchi, et al., 1980	LLK
C₃H₇⁺	11.16 ± 0.05	CH₃	EI	Williams and Hamill, 1968	RDSH
C₃H₇⁺	11.23 ± 0.03	CH₃	PI	Steiner, Giese, et al., 1961	RDSH
C₄H₉⁺	10.68 ± 0.02	H	PI	Mead, Donchi, et al., 1980	LLK
C₄H₉⁺	10.68 ± 0.03	H	PI	McLoughlin and Traeger, 1979	LLK
C₄H₉⁺	11.6	H	EI	Omura, 1961	RDSH

De-protonation reactions

C₄H₉^- + = Isobutane

By formula: C₄H₉^- + H⁺ = C₄H₁₀

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	1728. ± 8.4	kJ/mol	Bran	DePuy, Gronert, et al., 1989	gas phase; B
Δ_rH°	1735. ± 20.	kJ/mol	Bran	Peerboom, Rademaker, et al., 1992	gas phase; B
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	1692. ± 8.8	kJ/mol	H-TS	DePuy, Gronert, et al., 1989	gas phase; B
Δ_rG°	1699. ± 21.	kJ/mol	H-TS	Peerboom, Rademaker, et al., 1992	gas phase; B

C₄H₉^- + = Isobutane

By formula: C₄H₉^- + H⁺ = C₄H₁₀

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	1728. ± 8.4	kJ/mol	Bran	DePuy, Gronert, et al., 1989	gas phase; B
Δ_rH°	1732. ± 8.4	kJ/mol	Bran	DePuy, Bierbaum, et al., 1984	gas phase; B
Quantity	Value	Units	Method	Reference	Comment
Δ_rG°	1697. ± 8.8	kJ/mol	H-TS	DePuy, Gronert, et al., 1989	gas phase; B

References

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

Pittam and Pilcher, 1972
Pittam, D.A.; Pilcher, G., Measurements of heats of combustion by flame calorimetry. Part 8.-Methane, ethane, propane, n-butane and 2-methylpropane, J. Chem. Soc. Faraday Trans. 1, 1972, 68, 2224-2229. [all data]

Prosen, Maron, et al., 1951
Prosen, E.J.; Maron, F.W.; Rossini, F.D., Heats of combustion, formation, and insomerization of ten C₄ hydrocarbons, J. Res. NBS, 1951, 46, 106-112. [all data]

Prosen and Rossini, 1945
Prosen, E.J.; Rossini, F.D., Heats of formation and combustion of 1,3-butadiene and styrene, J. Res. NBS, 1945, 34, 59-63. [all data]

Rossini, 1935
Rossini, F.D., Heat of combustion of isobutane, J. Res. NBS, 1935, 15, 357-361. [all data]

Chen S.S., 1975
Chen S.S., Ideal gas thermodynamic properties and isomerization of n-butane and isobutane, J. Phys. Chem. Ref. Data, 1975, 4, 859-869. [all data]

Pitzer K.S., 1946
Pitzer K.S., The entropies and related properties of branched paraffin hydrocarbons, Chem. Rev., 1946, 39, 435-447. [all data]

Ernst G., 1970
Ernst G., Ideal and real gas state heat capacities Cp of C3H8, i-C4H10, C2F5Cl, CH2ClCF3, CF2ClCFCl2, and CHF2Cl, J. Chem. Thermodyn., 1970, 2, 787-791. [all data]

Sage B.H., 1937
Sage B.H., Phase equilibria in hydrocarbon systems. XX. Isobaric heat capacity of gaseous propane, n-butane, isobutane, and n-pentane, Ind. Eng. Chem., 1937, 29, 1309-1314. [all data]

Sage B.H., 1938
Sage B.H., Phase equilibrium in hydrocarbon systems. Thermodynamic properties of isobutane, Ind. Eng. Chem., 1938, 30, 673-681. [all data]

Dailey B.P., 1943
Dailey B.P., Heat capacities and hindered rotation in n-butane and isobutane, J. Am. Chem. Soc., 1943, 65, 44-46. [all data]

Wacker P.F., 1947
Wacker P.F., Heat capacities of gaseous oxygen, isobutane, and 1-butene from -30 to +90 C, J. Res. Nat. Bur. Stand., 1947, 38, 651-659. [all data]

Aston, Kennedy, et al., 1940
Aston, J.G.; Kennedy, R.M.; Schumann, S.C., The heat capacity and entropy, heats of fusion and vaporization and the vapor pressure of isobutane, J. Am. Chem. Soc., 1940, 62, 2059-2063. [all data]

Parks, Shomate, et al., 1937
Parks, G.S.; Shomate, C.H.; Kennedy, W.D.; Crawford, B.L., Jr., The entropies of n-butane and isobutane, with some heat capacity data for isobutane, J. Chem. Phys., 1937, 5, 359-363. [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]

Luo and Pacey, 1992
Luo, Y.-R.; Pacey, P.D., Effects of alkyl substitution on ionization energies of alkanes and haloalkanes and on heats of formation of their molecular cations. Part 2. Alkanes and chloro-, bromo- and iodoalkanes, Int. J. Mass Spectrom. Ion Processes, 1992, 112, 63. [all data]

Flesch and Svec, 1973
Flesch, G.D.; Svec, H.J., Fragmentation reactions in the mass spectrometer for C₂-C₅ alkanes, J. Chem. Soc. Faraday Trans. 2, 1973, 69, 1187. [all data]

Dewar and Worley, 1969
Dewar, M.J.S.; Worley, S.D., Photoelectron spectra of molecules. I. Ionization potentials of some organic molecules and their interpretation, J. Chem. Phys., 1969, 50, 654. [all data]

Turner and Al-Joboury, 1964
Turner, D.W.; Al-Joboury, M.I., Molecular photoelectron spectroscopy, Bull. Soc. Chim. Belges, 1964, 73, 428. [all data]

Al-Joboury and Turner, 1964
Al-Joboury, M.I.; Turner, D.W., Molecular photoelectron spectroscopy. Part II. A summary of ionization potentials, J. Chem. Soc., 1964, 4434. [all data]

Watanabe, Nakayama, et al., 1962
Watanabe, K.; Nakayama, T.; Mottl, J., Ionization potentials of some molecules, J. Quant. Spectry. Radiative Transfer, 1962, 2, 369. [all data]

Steiner, Giese, et al., 1961
Steiner, B.; Giese, C.F.; Inghram, M.G., Photoionization of alkanes. Dissociation of excited molecular ions, J. Chem. Phys., 1961, 34, 189. [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]

Murrell and Schmidt, 1972
Murrell, J.N.; Schmidt, W., Photoelectron spectroscopic correlation of the molecular orbitals of methane, ethane, propane, isobutane and neopentane, J. Chem. Soc. Faraday Trans. 2, 1972, 68, 1709. [all data]

Olmsted, Street, et al., 1964
Olmsted, J., III; Street, K., Jr.; Newton, A.S., Excess-kinetic-energy ions in organic mass spectra, J. Chem. Phys., 1964, 40, 2114. [all data]

Omura, 1961
Omura, I., Mass spectra at low ionizing voltage and bond dissociation energies of molecular ions from hydrocarbons, Bull. Chem. Soc. Japan, 1961, 34, 1227. [all data]

Mead, Donchi, et al., 1980
Mead, P.T.; Donchi, K.F.; Traeger, J.C.; Christie, J.R.; Derrick, P.J., Secondary hydrogen isotope effect in the unimolecular decomposition of 2-methylpropane radical cations, J. Am. Chem. Soc., 1980, 102, 3364. [all data]

Wolkoff and Holmes, 1978
Wolkoff, P.; Holmes, J.L., Fragmentations of alkane molecular ions, J. Am. Chem. Soc., 1978, 100, 7346. [all data]

Williams and Hamill, 1968
Williams, J.M.; Hamill, W.H., Ionization potentials of molecules and free radicals and appearance potentials by electron impact in the mass spectrometer, J. Chem. Phys., 1968, 49, 4467. [all data]

McLoughlin and Traeger, 1979
McLoughlin, R.G.; Traeger, J.C., Heat of formation for tert-butyl cation in the gas phase, J. Am. Chem. Soc., 1979, 101, 5791. [all data]

DePuy, Gronert, et al., 1989
DePuy, C.H.; Gronert, S.; Barlow, S.E.; Bierbaum, V.M.; Damrauer, R., The Gas Phase Acidities of the Alkanes, J. Am. Chem. Soc., 1989, 111, 6, 1968, https://doi.org/10.1021/ja00188a003 . [all data]

Peerboom, Rademaker, et al., 1992
Peerboom, R.A.L.; Rademaker, G.J.; Dekoning, L.J.; Nibbering, N.M.M., Stabilization of Cycloalkyl Carbanions in the Gas Phase, Rapid Commun. Mass Spectrom., 1992, 6, 6, 394, https://doi.org/10.1002/rcm.1290060608 . [all data]

DePuy, Bierbaum, et al., 1984
DePuy, C.H.; Bierbaum, V.M.; Damrauer, R., Relative Gas-Phase Acidities of the Alkanes, J. Am. Chem. Soc., 1984, 106, 4051. [all data]

Notes

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

Symbols used in this document:

AE	Appearance energy
C_p,gas	Constant pressure heat capacity of gas
C_p,liquid	Constant pressure heat capacity of liquid
IE (evaluated)	Recommended ionization energy
S°_liquid	Entropy of liquid at standard conditions
Δ_cH°_gas	Enthalpy of combustion of gas at standard conditions
Δ_fH°_gas	Enthalpy of formation of gas at standard conditions
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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