Benzene, hexamethyl-

Formula: C₁₂H₁₈
Molecular weight: 162.2713
IUPAC Standard InChI: InChI=1S/C12H18/c1-7-8(2)10(4)12(6)11(5)9(7)3/h1-6H3
IUPAC Standard InChIKey: YUWFEBAXEOLKSG-UHFFFAOYSA-N
CAS Registry Number: 87-85-4
Chemical structure:
This structure is also available as a 2d Mol file or as a computed 3d SD file
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Isotopologues:
- Hexamethylbenzene, deuterated
Other names: Hexamethylbenzene; Mellitene; 1,2,3,4,5,6-Hexamethylbenzene
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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
DRB - Donald R. Burgess, Jr.
GT - Glushko Thermocenter, Russian Academy of Sciences, Moscow

Quantity	Value	Units	Method	Reference	Comment
Δ_fH°_gas	-18.5 ± 0.60	kcal/mol	Ccb	Colomina, Jimenez, et al., 1989	see Boned, Colomina, et al., 1964; ALS
Δ_fH°_gas	-18.7	kcal/mol	N/A	Parks, West, et al., 1946	Value computed using Δ_fH_solid° value of -163.3±3.1 kj/mol from Parks, West, et al., 1946 and Δ_subH° value of 85.0 kj/mol from Parks, West, et al., 1946.; DRB

Constant pressure heat capacity of gas

C_p,gas (cal/mol*K)	Temperature (K)	Reference	Comment
44.07	200.	Draeger, 1985	Recommended values are in close agreement with experimental data on S(T). Discrepancies with earlier statistically calculated values [ Hastings S.H., 1957] amount to 16 and 13 J/mol*K in S(T) and Cp(T), respectively.; GT
54.33	273.15
57.72 ± 0.1	298.15
57.98	300.
71.30	400.
83.48	500.
94.12	600.
103.3	700.
111.1	800.
117.9	900.
123.8	1000.
128.8	1100.
133.2	1200.
137.0	1300.
140.2	1400.
143.1	1500.

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	-33.94	kcal/mol	Ccb	Oth, 1968	ALS
Quantity	Value	Units	Method	Reference	Comment
Δ_cH°_liquid	-1705.2 ± 1.7	kcal/mol	Ccb	Banse and Parks, 1933	Reanalyzed by Cox and Pilcher, 1970, Original value = -1703.88 kcal/mol; Corresponding Δ_fHº_liquid = -38.25 kcal/mol (simple calculation by NIST; no Washburn corrections); ALS
Quantity	Value	Units	Method	Reference	Comment
Δ_fH°_solid	-38.81 ± 0.60	kcal/mol	Ccb	Colomina, Jimenez, et al., 1989	see Boned, Colomina, et al., 1964; ALS
Δ_fH°_solid	-39.03 ± 0.73	kcal/mol	Ccb	Parks, West, et al., 1946	Reanalyzed by Cox and Pilcher, 1970, Original value = -39.19 ± 0.02 kcal/mol; ALS
Quantity	Value	Units	Method	Reference	Comment
Δ_cH°_solid	-1704.6 ± 0.45	kcal/mol	Ccb	Colomina, Jimenez, et al., 1989	see Boned, Colomina, et al., 1964; Corresponding Δ_fHº_solid = -38.81 kcal/mol (simple calculation by NIST; no Washburn corrections); ALS
Δ_cH°_solid	-1700.1 ± 1.3	kcal/mol	Ccb	Holdiness, 1984	Hf NR; Corresponding Δ_fHº_solid = -43.3 kcal/mol (simple calculation by NIST; no Washburn corrections); ALS
Δ_cH°_solid	-1704.42 ± 0.72	kcal/mol	Ccb	Parks, West, et al., 1946	Reanalyzed by Cox and Pilcher, 1970, Original value = -1704.29 ± 0.68 kcal/mol; Corresponding Δ_fHº_solid = -39.03 kcal/mol (simple calculation by NIST; no Washburn corrections); ALS
Quantity	Value	Units	Method	Reference	Comment
S°_{solid,1 bar}	72.373	cal/mol*K	N/A	Atake, Gyoten, et al., 1982	DH
S°_{solid,1 bar}	73.210	cal/mol*K	N/A	Frankosky and Aston, 1965	crystaline, I phase; DH
S°_{solid,1 bar}	74.00	cal/mol*K	N/A	Huffman, Parks, et al., 1930	crystaline, I phase; Extrapolation below 90 K, 82.38 J/mol*K.; DH

Constant pressure heat capacity of liquid

C_p,liquid (cal/mol*K)	Temperature (K)	Reference	Comment
88.60	455.	Kurbatov, 1947	T = 183 to 256°C, mean Cp, two temperatures.; DH

Constant pressure heat capacity of solid

C_p,solid (cal/mol*K)	Temperature (K)	Reference	Comment
58.17	298.15	Colomina, Jimenez, et al., 1989	DH
60.256	300.	Atake, Gyoten, et al., 1982	T = 3 to 300 K.; DH
58.709	298.15	Frankosky and Aston, 1965	crystaline, I phase; T = 13 to 340 K.; DH
61.21	293.81	Momotani, Suga, et al., 1956	T = 273 to 443 K. Unsmoothed experimental datum.; DH
61.78	303.	Spaght, Thomas, et al., 1932	crystaline, II phase; T = 30 to 200°C.; DH
60.90	294.6	Huffman, Parks, et al., 1930	crystaline, I phase; T = 85 to 294 K. Value is unsmoothed experimental datum.; DH

Reaction thermochemistry data

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Data compiled as indicated in comments:
ALS - Hussein Y. Afeefy, Joel F. Liebman, and Stephen E. Stein
M - Michael M. Meot-Ner (Mautner) and Sharon G. Lias

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

= Benzene, hexamethyl-

By formula: C₁₂H₁₈ = C₁₂H₁₈

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-82.5 ± 0.8	kcal/mol	Cm	Adam and Chang, 1969	liquid phase; solvent: Pure phase; Heat of isomerization; ALS
Δ_rH°	-91.2	kcal/mol	Eqk	Oth, 1968	liquid phase; Heat of isomerization, see Oth, 1969; ALS
Δ_rH°	-91.5	kcal/mol	Cm	Oth, 1968	liquid phase; solvent: Toluene-d8; Heat of isomerization at 150°C; ALS

= Benzene, hexamethyl-

By formula: C₁₂H₁₈ = C₁₂H₁₈

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-56.2 ± 0.6	kcal/mol	Cm	Adam and Chang, 1969	liquid phase; solvent: Pure phase; ALS
Δ_rH°	-59.5	kcal/mol	Eqk	Oth, 1968	liquid phase; Heat of isomerization, see Oth, 1969; ALS

C₆H₇N⁺ + Benzene, hexamethyl- = (C₆H₇N⁺ • )

By formula: C₆H₇N⁺ + C₁₂H₁₈ = (C₆H₇N⁺ • C₁₂H₁₈)

Bond type: Charge transfer bond (positive ion)

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	17.1	kcal/mol	PHPMS	Meot-Ner (Mautner) and El-Shall, 1986	gas phase; M
Quantity	Value	Units	Method	Reference	Comment
Δ_rS°	24.3	cal/mol*K	PHPMS	Meot-Ner (Mautner) and El-Shall, 1986	gas phase; M

= Benzene, hexamethyl-

By formula: C₁₂H₁₈ = C₁₂H₁₈

Quantity	Value	Units	Method	Reference	Comment
Δ_rH°	-42.7	kcal/mol	Ciso	Childs and Mulholland, 1983	liquid phase; ALS

References

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Colomina, Jimenez, et al., 1989
Colomina, M.; Jimenez, P.; Roux, M.V.; Turrion, C., Thermochemical properties of 1,2,4,5-tetramethylbenzene, pentamethylbenzene, and hexamethylbenzene, J. Chem. Thermodyn., 1989, 21, 275-281. [all data]

Boned, Colomina, et al., 1964
Boned, M.L.; Colomina, M.; Perez-Ossorio, R.; Turrion, C., Investigaciones termoquimicas sobre los polimetilbencenos superiores, Anal. Fisc. Quim. B, 1964, 60, 459-468. [all data]

Parks, West, et al., 1946
Parks, G.S.; West, T.J.; Naylor, B.F.; Fujii, P.S.; McClaine, L.A., Thermal data on organic compounds. XXIII. Modern combustion data for fourteen hydrocarbons and five polyhydroxy alcohols, J. Am. Chem. Soc., 1946, 68, 2524-2527. [all data]

Draeger, 1985
Draeger, J.A., The methylbenzenes II. Fundamental vibrational shifts, statistical thermodynamic functions, and properties of formation, J. Chem. Thermodyn., 1985, 17, 263-275. [all data]

Hastings S.H., 1957
Hastings S.H., Thermodynamic properties of selected methylbenzenes from 0 to 1000 K, J. Phys. Chem., 1957, 61, 730-735. [all data]

Oth, 1968
Oth, J.F.M., The kinetics and thermochemistry of the thermal rearrangement of hexamethylbicyclo[2.2.0]hexa-2,5-diene (hexamethyldewarbenzene) and of hexamethyltetracyclo[2.2.0,0(2,6).0(3,5)]hexane (hexamethylprismane), Chem. Ber., 1968, 47, 1185-1195. [all data]

Banse and Parks, 1933
Banse, H.; Parks, G.S., Thermal data on organic compounds. XII. The heats of combustion of nine hydrocarbons, J. Am. Chem. Soc., 1933, 55, 3223-3227. [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]

Holdiness, 1984
Holdiness, M.R., Resonance energy of hexaethylbenzene and hexamethylbenzene, Thermochim. Acta, 1984, 78, 435-436. [all data]

Atake, Gyoten, et al., 1982
Atake, T.; Gyoten, H.; Chihara, H., A concealed anomaly at 117.5 K in the heat capacity of hexamethylbenzene, J. Chem. Phys., 1982, 76(11), 5535-5540. [all data]

Frankosky and Aston, 1965
Frankosky, M.; Aston, J.G., The heat capacity and entropy of hexamethylbenzene from 13 to 340 K. An estimate of the internal rotation barrier, J. Phys. Chem., 1965, 69, 3126-3132. [all data]

Huffman, Parks, et al., 1930
Huffman, H.M.; Parks, G.S.; Daniels, A.C., Thermal data on organic compounds. VII. The heat capacities, entropies and free energies of twelve aromatic hydrocarbons, J. Am. Chem. Soc., 1930, 52, 1547-1558. [all data]

Kurbatov, 1947
Kurbatov, V.Ya., Specific heat of liquids. I. Specific heat of benzenoid hydrocarbons, Zhur. Obshch. Khim., 1947, 17, 1999-2003. [all data]

Momotani, Suga, et al., 1956
Momotani, M.; Suga, H.; Seki, S.; Nitta, I., Phase transitions in crystals composed of organic molecules with methyl groups at the molecular periperies, Proceed. National Academy of Sci. (India), XXV(Section A, part, 1956, II), 74-82. [all data]

Spaght, Thomas, et al., 1932
Spaght, M.E.; Thomas, S.B.; Parks, G.S., Some heat capacity data on organic compounds obtained with a radiation calorimeter, J. Phys. Chem., 1932, 36, 882-888. [all data]

Adam and Chang, 1969
Adam, W.; Chang, J.C., Kinetics and thermochemistry of valence isomerization by differential scanning calorimetry: the case of hexamethylprismane and hexamethyldewarbenzene, Int. J. Chem. Kinet., 1969, 1, 487-492. [all data]

Oth, 1969
Oth, J.F.M., The kinetics and thermochemistry of the thermal rearrangement of hexamethyl(Dewar benzene) and of hexamethylprismane, Angew. Chem. Int. Ed. Engl., 1969, 7, 646. [all data]

Meot-Ner (Mautner) and El-Shall, 1986
Meot-Ner (Mautner), M.; El-Shall, M.S., Ionic Charge Transfer Complexes. 1. Cationic Complexes with Delocalized and Partially Localized pi Systems, J. Am. Chem. Soc., 1986, 108, 15, 4386, https://doi.org/10.1021/ja00275a026 . [all data]

Childs and Mulholland, 1983
Childs, R.F.; Mulholland, D.L., Thermochemical relationships between some bicyclohexenyl and benzenium cations, J. Am. Chem. Soc., 1983, 105, 96-99. [all data]

Notes

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Symbols used in this document:

C_p,gas	Constant pressure heat capacity of gas
C_p,liquid	Constant pressure heat capacity of liquid
C_p,solid	Constant pressure heat capacity of solid
S°_{solid,1 bar}	Entropy of solid at standard conditions (1 bar)
Δ_cH°_liquid	Enthalpy of combustion of liquid at standard conditions
Δ_cH°_solid	Enthalpy of combustion of solid 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_fH°_solid	Enthalpy of formation of solid at standard conditions
Δ_rH°	Enthalpy of reaction at standard conditions
Δ_rS°	Entropy of reaction at standard conditions

Data from NIST Standard Reference Database 69: NIST Chemistry WebBook
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