CCCBDB listing of experimental data page 2

Other names
1,1-Dimethylethane; 2-Methylpropane; A 31; i-Butane; Isobutane; Isobutane mixtures; iso-C4H10; Liquefied petroleum gas; Propane, 2-methyl-; R 600a; tert-Butane; Trimethylmethane;

INChI	INChIKey	SMILES	IUPAC name
InChI=1S/C4H10/c1-4(2)3/h4H,1-3H3	NNPPMTNAJDCUHE-UHFFFAOYSA-N	CC(C)C	Isobutane

State	Conformation
¹A₁	C3V

Enthalpy of formation (Hfg), Entropy, Integrated heat capacity (0 K to 298.15 K) (HH), Heat Capacity (Cp)

Property	Value	Uncertainty	units	Reference	Comment
Hfg(298.15K)	-135.00	0.60	kJ mol^-1	TRC	unc from 1972Pit/Pil:2224
Hfg(0K)	-106.40	0.60	kJ mol^-1	TRC	unc from 1972Pit/Pil:2224
Entropy (298.15K)	295.50		J K^-1 mol^-1	TRC
Integrated Heat Capacity (0 to 298.15K)	17.93		kJ mol^-1	TRC
Heat Capacity (298.15K)	96.65		J K^-1 mol^-1	webbook

Information can also be found for this species in the NIST Chemistry Webbook

Vibrational levels (cm^-1) vibrations

Mode Number	Symmetry	Frequency			Intensity			Comment	Description
Mode Number	Symmetry	Fundamental(cm^-1)	Harmonic(cm^-1)	Reference	(km mol^-1)	unc.	Reference	Comment	Description
1	A₁	2965		1999Mir/Kri:67
2	A₁	2904
3	A₁	2880
4	A₁	1477
5	A₁	1394
6	A₁	1177
7	A₁	797
8	A₁	426
9	A₂
10	A₂
11	A₂
12	A₂	198		1999Mir/Kri:67
13	E	2962		1999Mir/Kri:67
14	E	2951
15	E	2887
16	E	1468
17	E	1459
18	E	1371
19	E	1330
20	E	1166
21	E	961
22	E	918
23	E	367
24	E	280

vibrational zero-point energy: 25229.0 cm^-1 (from fundamental vibrations)
Calculated vibrational frequencies for CH₃CH(CH₃)CH₃ (Isobutane).
Gas-phase IR spectra can be found in the NIST Chemistry Webbook here.

Rotational Constants (cm^-1)

See section I.F.4 to change rotational constant units

A	B	C	reference	comment
0.25979	0.25171	0.14780	1960Lide:1519

Calculated rotational constants for CH₃CH(CH₃)CH₃ (Isobutane).

Product of moments of inertia
495662.8	amu³Å⁶		2.26962599678587E-114	gm³ cm⁶

Geometric Data
picture of Isobutane

Point Group C_3v

Internal coordinates
distances (r) in Å, angles (a) in degrees, dihedrals (d) in degrees

Description	Value	unc.	Connectivity				Reference	Comment
Description	Value	unc.	Atom 1	Atom 2	Atom 3	Atom 4	Reference	Comment
rCC	1.525		1	3			1976Hellwege(II/7)
rCH	1.108		1	2			1976Hellwege(II/7)
rCH	1.100		3	6			1976Hellwege(II/7)	symmetric
rCH	1.092		3	9			1976Hellwege(II/7)	anti
aCCC	111.15		3	1	4		1976Hellwege(II/7)
aHCC	109.4		2	1	3		1976Hellwege(II/7)
aHCH	108.5		9	3	10		1976Hellwege(II/7)	anti-anti
aHCH	107.9		6	3	9		1976Hellwege(II/7)	anti-sym

Cartesians

Atom	x (Å)	y (Å)	z (Å)
C1	0.0000	0.0000	0.3650
H2	0.0000	0.0000	1.4730
C3	0.0000	1.4528	-0.0987
C4	1.2582	-0.7264	-0.0987
C5	-1.2582	-0.7264	-0.0987
H6	0.0000	1.4867	-1.1931
H7	1.2875	-0.7433	-1.1931
H8	-1.2875	-0.7433	-1.1931
H9	0.8941	1.9575	0.2821
H10	-0.8941	1.9575	0.2821
H11	1.2482	-1.7530	0.2821
H12	2.1422	-0.2045	0.2821
H13	-2.1422	-0.2045	0.2821
H14	-1.2482	-1.7530	0.2821

Atom - Atom Distances bond lengths

Distances in Å

	C1	H2	C3	C4	C5	H6	H7	H8	H9	H10	H11	H12	H13	H14
C1		1.1080	1.5250	1.5250	1.5250	2.1536	2.1536	2.1536	2.1536	2.1536	2.1536	2.1536	2.1536	2.1536
H2	1.1080		2.1403	2.1403	2.1403	3.0526	3.0526	3.0526	2.4595	2.4595	2.4595	2.4595	2.4595	2.4595
C3	1.5250	2.1403		2.5163	2.5163	1.0950	2.7710	2.7710	1.0950	1.0950	3.4613	2.7351	2.7351	3.4613
C4	1.5250	2.1403	2.5163		2.5163	2.7710	1.0950	2.7710	2.7351	3.4613	1.0950	1.0950	3.4613	2.7351
C5	1.5250	2.1403	2.5163	2.5163		2.7710	2.7710	1.0950	3.4613	2.7351	2.7351	3.4613	1.0950	1.0950
H6	2.1536	3.0526	1.0950	2.7710	2.7710		2.5750	2.5750	1.7881	1.7881	3.7722	3.1025	3.1025	3.7722
H7	2.1536	3.0526	2.7710	1.0950	2.7710	2.5750		2.5750	3.1025	3.7722	1.7881	1.7881	3.7722	3.1025
H8	2.1536	3.0526	2.7710	2.7710	1.0950	2.5750	2.5750		3.7722	3.1025	3.1025	3.7722	1.7881	1.7881
H9	2.1536	2.4595	1.0950	2.7351	3.4613	1.7881	3.1025	3.7722		1.7881	3.7273	2.4964	3.7273	4.2845
H10	2.1536	2.4595	1.0950	3.4613	2.7351	1.7881	3.7722	3.1025	1.7881		4.2845	3.7273	2.4964	3.7273
H11	2.1536	2.4595	3.4613	1.0950	2.7351	3.7722	1.7881	3.1025	3.7273	4.2845		1.7881	3.7273	2.4964
H12	2.1536	2.4595	2.7351	1.0950	3.4613	3.1025	1.7881	3.7722	2.4964	3.7273	1.7881		4.2845	3.7273
H13	2.1536	2.4595	2.7351	3.4613	1.0950	3.1025	3.7722	1.7881	3.7273	2.4964	3.7273	4.2845		1.7881
H14	2.1536	2.4595	3.4613	2.7351	1.0950	3.7722	3.1025	1.7881	4.2845	3.7273	2.4964	3.7273	1.7881

Calculated geometries for CH₃CH(CH₃)CH₃ (Isobutane).

Experimental Bond Angles (degrees) from cartesians

atom1	atom2	atom3	angle	atom1	atom2	atom3	angle
C1	C3	H6	109.471	C1	C3	H9	109.471
C1	C3	H10	109.471	C1	C4	H7	109.471
C1	C4	H11	109.471	C1	C4	H12	109.471
C1	C5	H8	109.471	C1	C5	H13	109.471
C1	C5	H14	109.471	H2	C1	C3	107.700
H2	C1	C4	107.700	H2	C1	C5	107.700
C3	C1	C4	111.183	C3	C1	C5	111.183
C4	C1	C5	111.183	H6	C3	H9	109.471
H6	C3	H10	109.471	H7	C4	H11	109.471
H7	C4	H12	109.471	H8	C5	H13	109.471
H8	C5	H14	109.471	H9	C3	H10	109.471
H11	C4	H12	109.471	H13	C5	H14	109.471

Bond descriptions

Examples: C-C single bond, C=C, double bond, C#C triple bond, C:C aromatic bond

Bond Type	Count
H-C	10
C-C	3

Connectivity

Atom 1	Atom 2
C1	H2
C1	C3
C1	C4
C1	C5
C3	H6
C3	H9
C3	H10
C4	H7
C4	H11
C4	H12
C5	H8
C5	H13
C5	H14

Electronic energy levels (cm^-1)

Energy (cm^-1)	Degeneracy	reference	description
0	1		¹A₁

Ionization Energies (eV)

Ionization Energy	I.E. unc.	vertical I.E.	v.I.E. unc.	reference
10.680	0.110	11.130		webbook

Dipole, Quadrupole and Polarizability
Electric dipole moment dipole

State	Config	State description	Conf description	Exp. min.	Dipole (Debye)				Reference	comment	Point Group	Components
State	Config	State description	Conf description	Exp. min.	x	y	z	total	Reference	comment	Point Group	dipole	quadrupole
1	1	¹A₁	C_3v	True				0.132	NSRDS-NBS10	MW	C_3v	1	1

Experimental dipole measurement abbreviations: MW microwave; DT Dielectric with Temperature variation; DR Indirect (usually an upper limit); MB Molecular beam
Calculated electric dipole moments for CH₃CH(CH₃)CH₃ (Isobutane).
Electric quadrupole moment

State	Config	State description	Conf description	Exp. min.	Quadrupole (D Å)			Reference	comment	Point Group	Components
State	Config	State description	Conf description	Exp. min.	xx	yy	zz	Reference	comment	Point Group	dipole	quadrupole
1	1	¹A₁	C_3v	True						C_3v	1	1

Calculated electric quadrupole moments for CH₃CH(CH₃)CH₃ (Isobutane).
Electric dipole polarizability (Å³)

alpha	unc.	Reference
8.009		1998Gus/Rui:163

Calculated electric dipole polarizability for CH₃CH(CH₃)CH₃ (Isobutane).

References
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squib	reference	DOI
1960Lide:1519	Dr Lide "STRUCTURE OF THE ISOBUTANE MOLECULE - CHANGE OF DIPOLE MOMENT ON ISOTOPIC SUBSTITUTION" J. Chem. Phys. 33(5) 1519-1522, 1960	10.1063/1.1731435
1976Hellwege(II/7)	Hellwege, KH and AM Hellwege (ed.). Landolt-Bornstein: Group II: Atomic and Molecular Physics Volume 7: Structure Data of Free Polyatomic Molecules. Springer-Verlag. Berlin. 1976.
1998Gus/Rui:163	M Gussoni, R Rui, G Zerbi "Electronic and relaxation contribution to linear molecular polarizability. An analysis of the experimental values" J. Mol. Struct. 447 (1998) 163-215	10.1016/S0022-2860(97)00292-5
1999Mir/Kri:67	NG Mirkin, S Krimm "Ab inito analysis of the vibrational spectra of conformers of some branched alkanes" J. Mol. Struct. 550-551 (2000) 67-91	10.1016/S0022-2860(00)00513-5
NSRDS-NBS10	R. D. Nelson Jr., D. R. Lide, A. A. Maryott "Selected Values of electric dipole moments for molecules in the gas phase" NSRDS-NBS10, 1967	10.6028/NBS.NSRDS.10
TRC	Frenkel, M; Marsh, K.N.; Wilhoit, R.C.; Kabo, G.J.; Roganov, G.N.,Thermodynamics of Organic Compounds in the Gas State,Thermodynamics Research Center, College Station, TX, 1994
webbook	NIST Chemistry Webbook (http://webbook.nist.gov/chemistry)	10.18434/T4D303

Got a better number? Please email us at cccbdb@nist.gov

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Experimental data for CH3CH(CH3)CH3 (Isobutane)

Experimental data for CH₃CH(CH₃)CH₃ (Isobutane)