Butane, 2-methyl-

Formula: C₅H₁₂
Molecular weight: 72.1488
IUPAC Standard InChI: InChI=1S/C5H12/c1-4-5(2)3/h5H,4H2,1-3H3
IUPAC Standard InChIKey: QWTDNUCVQCZILF-UHFFFAOYSA-N
CAS Registry Number: 78-78-4
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: iso-Pentane; 1,1,2-Trimethylethane; 2-Methylbutane; iso-C5H12; Ethyldimethylmethane; Isoamylhydride; Exxsol isopentane S; 1,1-Dimethylpropane; Methylbutane; NSC 119476
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Gas phase thermochemistry data

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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	-36.73 ± 0.14	kcal/mol	Ccb	Good, 1970	ALS
Δ_fH°_gas	-36.84 ± 0.23	kcal/mol	Cm	Pilcher and Chadwick, 1967	ALS
Δ_fH°_gas	-36.92 ± 0.20	kcal/mol	Ccb	Prosen and Rossini, 1945	ALS
Quantity	Value	Units	Method	Reference	Comment
Δ_cH°_gas	-843.31 ± 0.22	kcal/mol	Cm	Pilcher and Chadwick, 1967	Corresponding Δ_fHº_gas = -36.84 kcal/mol (simple calculation by NIST; no Washburn corrections); ALS
Δ_cH°_gas	-843.36 ± 0.15	kcal/mol	Cm	Knowlton and Rossini, 1939	Corresponding Δ_fHº_gas = -36.79 kcal/mol (simple calculation by NIST; no Washburn corrections); ALS
Δ_cH°_gas	-843.11 ± 0.84	kcal/mol	Ccb	Roth and Pahlke, 1936	Reanalyzed by Cox and Pilcher, 1970, Original value = -843.45 kcal/mol; Corresponding Δ_fHº_gas = -37.04 kcal/mol (simple calculation by NIST; no Washburn corrections); ALS

Constant pressure heat capacity of gas

C_p,gas (cal/mol*K)	Temperature (K)	Reference	Comment
20.30	200.	Scott D.W., 1974	Recommended values were obtained from the consistent correlation scheme for alkanes [ Scott D.W., 1974, 2, Scott D.W., 1974]. This approach gives a better agreement with experimental data than the statistical thermodynamics calculations [ Pitzer K.S., 1946, Scott D.W., 1951].; GT
26.379	273.15
28.41 ± 0.1	298.15
28.561	300.
36.539	400.
43.800	500.
50.201	600.
55.700	700.
60.500	800.
64.699	900.
68.401	1000.
71.599	1100.
74.400	1200.
77.000	1300.
79.001	1400.
80.999	1500.

Constant pressure heat capacity of gas

C_p,gas (cal/mol*K)	Temperature (K)	Reference	Comment
29.950 ± 0.088	317.20	Scott D.W., 1951	GT
33.25 ± 0.10	358.15
36.72 ± 0.11	402.30
40.24 ± 0.12	449.20
42.93 ± 0.13	487.05

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	-42.58 ± 0.21	kcal/mol	Ccb	Good, 1970	Reanalyzed by Pedley, Naylor, et al., 1986, Original value = -42.76 ± 0.14 kcal/mol; ALS
Δ_fH°_liquid	-42.86 ± 0.20	kcal/mol	Ccb	Prosen and Rossini, 1945	ALS
Quantity	Value	Units	Method	Reference	Comment
Δ_cH°_liquid	-837.57 ± 0.20	kcal/mol	Ccb	Good, 1970	Reanalyzed by Pedley, Naylor, et al., 1986, Original value = -837.39 ± 0.11 kcal/mol; Corresponding Δ_fHº_liquid = -42.58 kcal/mol (simple calculation by NIST; no Washburn corrections); ALS
Δ_cH°_liquid	-837.30 ± 0.18	kcal/mol	Ccb	Prosen and Rossini, 1945	Corresponding Δ_fHº_liquid = -42.85 kcal/mol (simple calculation by NIST; no Washburn corrections); ALS
Quantity	Value	Units	Method	Reference	Comment
S°_liquid	62.239	cal/mol*K	N/A	Guthrie and Huffman, 1943	DH
S°_liquid	62.390	cal/mol*K	N/A	Schumann, Aston, et al., 1942	DH
S°_liquid	60.80	cal/mol*K	N/A	Parks, Huffman, et al., 1930	Extrapolation below 90 K, 57.49 J/mol*K.; DH

Constant pressure heat capacity of liquid

C_p,liquid (cal/mol*K)	Temperature (K)	Reference	Comment
39.32	298.3	Czarnota, 1988	T = 289 to 299 K. p = 0.1 MPa. Unsmoothed experimental datum. Cp values provided over the pressure range 0.1 to 820 MPa.; DH
39.400	298.15	Guthrie and Huffman, 1943	T = 13 to 300 K.; DH
40.490	290.	Schumann, Aston, et al., 1942	T = 20 to 290 K.; DH
37.60	275.8	Parks, Huffman, et al., 1930	T = 80 to 276 K. Value is unsmoothed experimental datum.; DH

Reaction thermochemistry data

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Data compiled by: Hussein Y. Afeefy, Joel F. Liebman, and Stephen E. Stein

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Individual Reactions

+ = Butane, 2-methyl-

By formula: H₂ + C₅H₁₀ = C₅H₁₂

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-30.341	kcal/mol	Chyd	Dolliver, Gresham, et al., 1937	gas phase; At 355 °K
Δ_rH°	-28.25 ± 0.10	kcal/mol	Chyd	Kistiakowsky, Ruhoff, et al., 1936	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -28.49 ± 0.36 kcal/mol; At 355 K

+ = Butane, 2-methyl-

By formula: H₂ + C₅H₁₀ = C₅H₁₂

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-30.19 ± 0.06	kcal/mol	Chyd	Dolliver, Gresham, et al., 1937	gas phase; Reanalyzed by Cox and Pilcher, 1970, Original value = -30.34 ± 0.06 kcal/mol; At 355 °K

= Butane, 2-methyl-

By formula: C₅H₁₂ = C₅H₁₂

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-1.861	kcal/mol	Eqk	Pines, Kvetinskas, et al., 1945	gas phase; Heat of isomerization

+ = Butane, 2-methyl-

By formula: H₂ + C₅H₁₀ = C₅H₁₂

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-26.68 ± 0.06	kcal/mol	Chyd	Kistiakowsky, Ruhoff, et al., 1936	gas phase

Gas phase ion energetics data

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Data evaluated as indicated in comments:
L - Sharon G. Lias

Data compiled as indicated in comments:
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)	10.32 ± 0.05	eV	N/A	N/A	L

Ionization energy determinations

IE (eV)	Method	Reference	Comment
10.21	PI	Traeger, Hudson, et al., 1996	T = 0K; LL
10.18	EST	Luo and Pacey, 1992	LL
10.22	PI	Traeger, 1981	LLK
10.3 ± 0.1	PE	Bieri, Burger, et al., 1977	LLK
10.50 ± 0.05	EI	Flesch and Svec, 1973	LLK
10.32	PE	Dewar and Worley, 1969	RDSH
10.32	PI	Watanabe, Nakayama, et al., 1962	RDSH
10.94	PE	Kimura, Katsumata, et al., 1981	Vertical value; LLK
11.0 ± 0.1	PE	Bieri, Burger, et al., 1977	Vertical value; LLK

Appearance energy determinations

Ion	AE (eV)	Other Products	Method	Reference	Comment
C₃H₆⁺	10.66	C₂H₆	PI	Traeger, Hudson, et al., 1996	T = 0K; LL
C₃H₆⁺	10.84 ± 0.025	C₂H₆	PI	Steiner, Giese, et al., 1961	RDSH
C₃H₇⁺	11.06	C₂H₅	PI	Traeger, Hudson, et al., 1996	T = 0K; LL
C₃H₇⁺	11.15 ± 0.05	C₂H₅	PI	Steiner, Giese, et al., 1961	RDSH
C₄H₈⁺	10.72	CH₄	PI	Traeger, Hudson, et al., 1996	T = 0K; LL
C₄H₈⁺	10.74 ± 0.02	CH₄	PI	Steiner, Giese, et al., 1961	RDSH
C₄H₉⁺	10.96	CH₃	PI	Traeger, Hudson, et al., 1996	T = 0K; LL
C₄H₉⁺	10.87	CH₃	PI	Traeger, 1981	LLK
C₄H₉⁺	11.15 ± 0.07	CH₃	PI	Steiner, Giese, et al., 1961	RDSH

References

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

Good, 1970
Good, W.D., The enthalpies of combustion and formation of the isomeric pentanes, J. Chem. Thermodyn., 1970, 2, 237-244. [all data]

Pilcher and Chadwick, 1967
Pilcher, G.; Chadwick, J.D.M., Measurements of heats of combustion by flame calorimetry. Part 4.-n-Pentane, isopentane, neopentane, Trans. Faraday Soc., 1967, 63, 2357-2361. [all data]

Prosen and Rossini, 1945
Prosen, E.J.; Rossini, F.D., Heats of combustion and formation of the paraffin hydrocarbons at 25° C, J. Res. NBS, 1945, 263-267. [all data]

Knowlton and Rossini, 1939
Knowlton, J.W.; Rossini, F.D., Heats of combustion of tetramethylmethane and 2-methylbutane, J. Res. NBS, 1939, 22, 415-424. [all data]

Roth and Pahlke, 1936
Roth, W.A.; Pahlke, H., Sekundare eichsubstanz fur verbrennungscalorimeter fur gase und dampfe. Die verbrennungswarme von isopentandampf, Angew. Chem., 1936, 49, 618-619. [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]

Scott D.W., 1974
Scott D.W., Chemical Thermodynamic Properties of Hydrocarbons and Related Substances. Properties of the Alkane Hydrocarbons, C1 through C10 in the Ideal Gas State from 0 to 1500 K. U.S. Bureau of Mines, Bulletin 666, 1974. [all data]

Scott D.W., 1974, 2
Scott D.W., Correlation of the chemical thermodynamic properties of alkane hydrocarbons, J. Chem. Phys., 1974, 60, 3144-3165. [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]

Scott D.W., 1951
Scott D.W., Rotational isomerism and thermodynamic functions of 2-methylbutane and 2,3-dimethylbutane. Vapor heat capacity and heat of vaporization of 2-methylbutane, J. Am. Chem. Soc., 1951, 73, 1707-1712. [all data]

Pedley, Naylor, et al., 1986
Pedley, J.B.; Naylor, R.D.; Kirby, S.P., Thermochemical Data of Organic Compounds, Chapman and Hall, New York, 1986, 1-792. [all data]

Guthrie and Huffman, 1943
Guthrie, G.B., Jr.; Huffman, H.M., Thermal data. XVI. The heat capacity and entropy of isopentane. The absence of a reported anomaly, J. Am. Chem. Soc., 1943, 65, 1139-1143. [all data]

Schumann, Aston, et al., 1942
Schumann, S.C.; Aston, J.G.; Sagenkahn, M., The heat capacity and entropy, heats of fusion and vaporization and the vapor pressures of isopentane, J. Am. Chem. Soc., 1942, 64, 1039-1043. [all data]

Parks, Huffman, et al., 1930
Parks, G.S.; Huffman, H.M.; Thomas, S.B., Thermal data on organic compounds. VI. The heat capacities, entropies and free energies of some saturated, non-benzenoid hydrocarbons, J. Am. Chem. Soc., 1930, 52, 1032-1041. [all data]

Czarnota, 1988
Czarnota, I., Heat capacity of 2-methylbutane at high pressures, J. Chem. Thermodynam., 1988, 20, 457-462. [all data]

Dolliver, Gresham, et al., 1937
Dolliver, M.a.; Gresham, T.L.; Kistiakowsky, G.B.; Vaughan, W.E., Heats of organic reactions. V. Heats of hydrogenation of various hydrocarbons, J. Am. Chem. Soc., 1937, 59, 831-841. [all data]

Kistiakowsky, Ruhoff, et al., 1936
Kistiakowsky, G.B.; Ruhoff, J.R.; Smith, H.A.; Vaughan, W.E., Heats of organic reactions. III. Hydrogenation of some higher olefins, J. Am. Chem. Soc., 1936, 58, 137-145. [all data]

Pines, Kvetinskas, et al., 1945
Pines, H.; Kvetinskas, B.; Kassel, L.S.; Ipatieff, V.N., Determination of equilibrium constants for butanes and pentanes, J. Am. Chem. Soc., 1945, 67, 631-637. [all data]

Traeger, Hudson, et al., 1996
Traeger, J.C.; Hudson, C.E.; McAdoo, D.J., A photoionization study of the ion-neutral complexes [CH₃CH⁺CH₃CH₂CH₃] and [CH₃CH₂CH⁺CH₃CH₃] in the gas phase: Formation, H-transfer and C-C bond formation between partners, and channeling of energy into dissociation, J. Am. Soc. Mass Spectrom., 1996, 7, 73. [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]

Traeger, 1981
Traeger, J.C., Heat of formation of sec-butyl cation in the gas phase, Org. Mass Spectrom., 1981, 16, 193. [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]

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]

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]

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]

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]

Notes

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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_cH°_liquid	Enthalpy of combustion of liquid at standard conditions
Δ_fH°_gas	Enthalpy of formation of gas 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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