Benzene, hexamethyl-

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Condensed phase thermochemistry data

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Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.

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
Δfliquid-142.0kJ/molCcbOth, 1968ALS
Quantity Value Units Method Reference Comment
Δcliquid-7134.6 ± 7.1kJ/molCcbBanse and Parks, 1933Reanalyzed by Cox and Pilcher, 1970, Original value = -7129.03 kJ/mol; Corresponding Δfliquid = -160.0 kJ/mol (simple calculation by NIST; no Washburn corrections); ALS
Quantity Value Units Method Reference Comment
Δfsolid-162.4 ± 2.5kJ/molCcbColomina, Jimenez, et al., 1989see Boned, Colomina, et al., 1964; ALS
Δfsolid-163.3 ± 3.1kJ/molCcbParks, West, et al., 1946Reanalyzed by Cox and Pilcher, 1970, Original value = -164.0 ± 0.08 kJ/mol; ALS
Quantity Value Units Method Reference Comment
Δcsolid-7132.2 ± 1.9kJ/molCcbColomina, Jimenez, et al., 1989see Boned, Colomina, et al., 1964; Corresponding Δfsolid = -162.4 kJ/mol (simple calculation by NIST; no Washburn corrections); ALS
Δcsolid-7113.2 ± 5.2kJ/molCcbHoldiness, 1984Hf NR; Corresponding Δfsolid = -181. kJ/mol (simple calculation by NIST; no Washburn corrections); ALS
Δcsolid-7131.3 ± 3.0kJ/molCcbParks, West, et al., 1946Reanalyzed by Cox and Pilcher, 1970, Original value = -7130.7 ± 2.8 kJ/mol; Corresponding Δfsolid = -163.3 kJ/mol (simple calculation by NIST; no Washburn corrections); ALS
Quantity Value Units Method Reference Comment
solid,1 bar302.81J/mol*KN/AAtake, Gyoten, et al., 1982DH
solid,1 bar306.31J/mol*KN/AFrankosky and Aston, 1965crystaline, I phase; DH
solid,1 bar309.6J/mol*KN/AHuffman, Parks, et al., 1930crystaline, I phase; Extrapolation below 90 K, 82.38 J/mol*K.; DH

Constant pressure heat capacity of liquid

Cp,liquid (J/mol*K) Temperature (K) Reference Comment
370.7455.Kurbatov, 1947T = 183 to 256°C, mean Cp, two temperatures.; DH

Constant pressure heat capacity of solid

Cp,solid (J/mol*K) Temperature (K) Reference Comment
243.4298.15Colomina, Jimenez, et al., 1989DH
252.11300.Atake, Gyoten, et al., 1982T = 3 to 300 K.; DH
245.64298.15Frankosky and Aston, 1965crystaline, I phase; T = 13 to 340 K.; DH
256.1293.81Momotani, Suga, et al., 1956T = 273 to 443 K. Unsmoothed experimental datum.; DH
258.5303.Spaght, Thomas, et al., 1932crystaline, II phase; T = 30 to 200°C.; DH
254.8294.6Huffman, Parks, et al., 1930crystaline, I phase; T = 85 to 294 K. Value is unsmoothed experimental datum.; DH

Phase change data

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Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.

Data compiled as indicated in comments:
BS - Robert L. Brown and Stephen E. Stein
TRC - Thermodynamics Research Center, NIST Boulder Laboratories, Chris Muzny director
AC - William E. Acree, Jr., James S. Chickos
ALS - Hussein Y. Afeefy, Joel F. Liebman, and Stephen E. Stein
DRB - Donald R. Burgess, Jr.
CAL - James S. Chickos, William E. Acree, Jr., Joel F. Liebman, Students of Chem 202 (Introduction to the Literature of Chemistry), University of Missouri -- St. Louis
DH - Eugene S. Domalski and Elizabeth D. Hearing

Quantity Value Units Method Reference Comment
Tboil538.2KN/AWeast and Grasselli, 1989BS
Tboil536.85KN/ACooper, Crowne, et al., 1967Uncertainty assigned by TRC = 0.6 K; TRC
Quantity Value Units Method Reference Comment
Tfus438. ± 3.KAVGN/AAverage of 13 values; Individual data points
Quantity Value Units Method Reference Comment
Tc758. ± 1.KN/ATsonopoulos and Ambrose, 1995 
Tc758.KN/AAmbrose, Broderick, et al., 1974Uncertainty assigned by TRC = 2. K; TRC
Tc751.15KN/AGuye and Mallet, 1902Uncertainty assigned by TRC = 10. K; crit. temp. greater than this - sample decomposes at this T; TRC
Quantity Value Units Method Reference Comment
Δvap68.6kJ/molCGCZhao, Unhannanant, et al., 2008AC
Quantity Value Units Method Reference Comment
Δsub83. ± 7.kJ/molAVGN/AAverage of 7 values; Individual data points

Enthalpy of vaporization

ΔvapH (kJ/mol) Temperature (K) Method Reference Comment
56.8458.AStephenson and Malanowski, 1987Based on data from 443. to 537. K.; AC

Enthalpy of sublimation

ΔsubH (kJ/mol) Temperature (K) Method Reference Comment
85.2320.AAmbrose, Lawrenson, et al., 1976Based on data from 303. to 338. K.; AC
83.2329.AOverberger, Steele, et al., 1969Based on data from 314. to 364. K.; AC

Enthalpy of fusion

ΔfusH (kJ/mol) Temperature (K) Reference Comment
20.63438.7Domalski and Hearing, 1996See also Spaght, Thomas, et al., 1931.; AC

Entropy of fusion

ΔfusS (J/mol*K) Temperature (K) Reference Comment
4.58383.7Domalski and Hearing, 1996CAL
47.02438.7

Temperature of phase transition

Ttrs (K) Initial Phase Final Phase Reference Comment
382.crystaline, IIIcrystaline, IFujiwara, Inaba, et al., 1992DH
439.crystaline, IliquidFujiwara, Inaba, et al., 1992DH

Enthalpy of phase transition

ΔHtrs (kJ/mol) Temperature (K) Initial Phase Final Phase Reference Comment
1.100117.5crystaline, IIIcrystaline, IIFujiwara, Inaba, et al., 1992From Atake, Gyoten, et al., 1982; DH
1.500384.0crystaline, IIcrystaline, IPetropavlov, Tsygankova, et al., 1988DH
1.103115.5crystaline, IIcrystaline, IYoshimoto, Fujiwara, et al., 1985DH
0.990117.5crystaline, IIIcrystaline, IIAtake, Gyoten, et al., 1982First order transition.; DH
1.1284116.48crystaline, IIcrystaline, IFrankosky and Aston, 1965Entropy obtained as difference of integral of observed Cp over range 115 to 128 K, and integral of extrapolated Cp data.; DH
1.841383.55crystaline, IIcrystaline, IMomotani, Suga, et al., 1956DH
20.585438.35crystaline, IliquidMomotani, Suga, et al., 1956DH
1.766383.7crystaline, IIcrystaline, ISpaght, Thomas, et al., 1932DH
20.640438.7crystaline, IliquidSpaght, Thomas, et al., 1932DH
1.017108.crystaline, IIIcrystaline, IIHuffman, Parks, et al., 1930DH
0.155151.crystaline, IIcrystaline, IHuffman, Parks, et al., 1930DH

Entropy of phase transition

ΔStrs (J/mol*K) Temperature (K) Initial Phase Final Phase Reference Comment
9.3117.5crystaline, IIIcrystaline, IIFujiwara, Inaba, et al., 1992From; DH
3.9384.0crystaline, IIcrystaline, IPetropavlov, Tsygankova, et al., 1988DH
9.55115.5crystaline, IIcrystaline, IYoshimoto, Fujiwara, et al., 1985DH
8.3117.5crystaline, IIIcrystaline, IIAtake, Gyoten, et al., 1982First; DH
10.08116.48crystaline, IIcrystaline, IFrankosky and Aston, 1965Entropy; DH
4.81383.55crystaline, IIcrystaline, IMomotani, Suga, et al., 1956DH
46.86438.35crystaline, IliquidMomotani, Suga, et al., 1956DH
4.60383.7crystaline, IIcrystaline, ISpaght, Thomas, et al., 1932DH
47.0438.7crystaline, IliquidSpaght, Thomas, et al., 1932DH
9.5108.crystaline, IIIcrystaline, IIHuffman, Parks, et al., 1930DH
1.0151.crystaline, IIcrystaline, IHuffman, Parks, et al., 1930DH

In addition to the Thermodynamics Research Center (TRC) data available from this site, much more physical and chemical property data is available from the following TRC products:


Gas phase ion energetics data

Go To: Top, Condensed phase thermochemistry data, Phase change data, References, Notes

Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.

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

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

View reactions leading to C12H18+ (ion structure unspecified)

Quantity Value Units Method Reference Comment
IE (evaluated)7.85 ± 0.01eVN/AN/AL
Quantity Value Units Method Reference Comment
Proton affinity (review)860.6kJ/molN/AHunter and Lias, 1998HL
Quantity Value Units Method Reference Comment
Gas basicity836.0kJ/molN/AHunter and Lias, 1998HL

Electron affinity determinations

EA (eV) Method Reference Comment
<0.121 ± 0.017ECDWojnarovits and Foldiak, 1981EA is an upper limit: Chen and Wentworth, 1989. G3MP2B3 calculations indicate an EA of ca. -0.1 eV, anion unbound.; B

Ionization energy determinations

IE (eV) Method Reference Comment
7.85PEHowell, Goncalves, et al., 1984LBLHLM
7.87EIKuznesof, Stafford, et al., 1967RDSH
7.85 ± 0.02PIVilesov, 1961RDSH
7.85PIBralsford, Harris, et al., 1960RDSH
7.8CTSFoster, 1959RDSH
7.95CTSBriegleb and Czekalla, 1959RDSH
7.85PEHowell, Goncalves, et al., 1984Vertical value; LBLHLM
7.9PEKovac, Mohraz, et al., 1980Vertical value; LLK

References

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

Data compilation copyright by the U.S. Secretary of Commerce on behalf of the U.S.A. All rights reserved.

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]

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]

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]

Weast and Grasselli, 1989
CRC Handbook of Data on Organic Compounds, 2nd Editon, Weast,R.C and Grasselli, J.G., ed(s)., CRC Press, Inc., Boca Raton, FL, 1989, 1. [all data]

Cooper, Crowne, et al., 1967
Cooper, A.R.; Crowne, C.W.P.; Farrell, P.G., Gas-Liquid Chromatographic Studies of Electron-Donor-Acceptor Systems, Trans. Faraday Soc., 1967, 63, 447. [all data]

Tsonopoulos and Ambrose, 1995
Tsonopoulos, C.; Ambrose, D., Vapor-Liquid Critical Properties of Elements and Compounds. 3. Aromatic Hydrocarbons, J. Chem. Eng. Data, 1995, 40, 547-558. [all data]

Ambrose, Broderick, et al., 1974
Ambrose, D.; Broderick, B.E.; Townsend, R., The Critical Temperatures and Pressures of Thirty Organic Compounds, J. Appl. Chem. Biotechnol., 1974, 24, 359. [all data]

Guye and Mallet, 1902
Guye, P.A.; Mallet, E., Measurement of Critical Constants, Arch. Sci. Phys. Nat., 1902, 13, 274-296. [all data]

Zhao, Unhannanant, et al., 2008
Zhao, Hui; Unhannanant, Patamaporn; Hanshaw, William; Chickos, James S., Enthalpies of Vaporization and Vapor Pressures of Some Deuterated Hydrocarbons. Liquid-Vapor Pressure Isotope Effects, J. Chem. Eng. Data, 2008, 53, 7, 1545-1556, https://doi.org/10.1021/je800091s . [all data]

Stephenson and Malanowski, 1987
Stephenson, Richard M.; Malanowski, Stanislaw, Handbook of the Thermodynamics of Organic Compounds, 1987, https://doi.org/10.1007/978-94-009-3173-2 . [all data]

Ambrose, Lawrenson, et al., 1976
Ambrose, D.; Lawrenson, I.J.; Sprake, C.H.S., The vapour pressure of hexamethylbenzene, The Journal of Chemical Thermodynamics, 1976, 8, 5, 503-504, https://doi.org/10.1016/0021-9614(76)90071-9 . [all data]

Overberger, Steele, et al., 1969
Overberger, John E.; Steele, William A.; Aston, John G., The vapor pressure of hexamethylbenzene the standard entropy of hexamethylbenzene vapor and the barrier to internal rotation, The Journal of Chemical Thermodynamics, 1969, 1, 6, 535-542, https://doi.org/10.1016/0021-9614(69)90014-7 . [all data]

Domalski and Hearing, 1996
Domalski, Eugene S.; Hearing, Elizabeth D., Heat Capacities and Entropies of Organic Compounds in the Condensed Phase. Volume III, J. Phys. Chem. Ref. Data, 1996, 25, 1, 1, https://doi.org/10.1063/1.555985 . [all data]

Spaght, Thomas, et al., 1931
Spaght, M.E.; Thomas, S.B.; Parks, G.S., Some Heat-Capacity Data on Organic Compounds obtained with a Radiation Calorimeter, J. Phys. Chem., 1931, 36, 3, 882-888, https://doi.org/10.1021/j150333a009 . [all data]

Fujiwara, Inaba, et al., 1992
Fujiwara, T.; Inaba, A.; Atake, T.; Chihara, H., Thermodynamic properties of deuterated hexamethylbenzene and of its solid solutions with the hydrogenated analog. A large isotope effect on the phase transition at the temperature 117 K, J. Chem. Thermodynam., 1992, 24, 863-881. [all data]

Petropavlov, Tsygankova, et al., 1988
Petropavlov, N.N.; Tsygankova, I.G.; Teslenko, L.A., Microcalorimetric investigation of polymorphic transitions in organic crystals, Sov. Phys. Crystallogr., 1988, 33(6), 853-855. [all data]

Yoshimoto, Fujiwara, et al., 1985
Yoshimoto, Y.; Fujiwara, T.; Atake, T.; Chihara, H., Solid-solid transition in hexamethylbenzene that depends on thermal history, Chem. Lett., 1985, (9), 1347-1350. [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]

Wojnarovits and Foldiak, 1981
Wojnarovits, L.; Foldiak, G., Electron capture detection of aromatic hydrocarbons, J. Chromatogr. Sci., 1981, 206, 511. [all data]

Chen and Wentworth, 1989
Chen, E.C.M.; Wentworth, W.E., Experimental Determination of Electron Affinities of Organic Molecules, Mol. Cryst. Liq. Cryst., 1989, 171, 271. [all data]

Howell, Goncalves, et al., 1984
Howell, J.O.; Goncalves, J.M.; Amatore, C.; Klasinc, L.; Wightman, R.M.; Kochi, J.K., Electron transfer from aromatic hydrocarbons and their π-complexes with metals. Comparison of the standard oxidation potentials and vertical ionization potentials, J. Am. Chem. Soc., 1984, 106, 3968. [all data]

Kuznesof, Stafford, et al., 1967
Kuznesof, P.M.; Stafford, F.E.; Shriver, D.F., Electron impact ionization potentials of methyl-substituted borazines, J. Phys. Chem., 1967, 71, 1939. [all data]

Vilesov, 1961
Vilesov, F.I., Photoionisation of organic vapours in the vacuum ultra-violet, Zh. Fiz. Khim., 1961, 35, 2010, In original 986. [all data]

Bralsford, Harris, et al., 1960
Bralsford, R.; Harris, P.V.; Price, W.C., The effect of fluorine on the electronic spectra and ionization potentials of molecules, Proc. Roy. Soc. (London), 1960, A258, 459. [all data]

Foster, 1959
Foster, R., Ionization potentials of electron donors, Nature (London), 1959, 183, 1253. [all data]

Briegleb and Czekalla, 1959
Briegleb, G.; Czekalla, J., Die Bestimmung von lonisierungsenergien aus den Spektren von Elektronenubergangskomplexen, Z.Elektrochem., 1959, 63, 6. [all data]

Kovac, Mohraz, et al., 1980
Kovac, B.; Mohraz, M.; Heilbronner, E.; Boekelheide, V.; Hopf, H., Photoelectron spectra of the cyclophanes, J. Am. Chem. Soc., 1980, 102, 4314. [all data]


Notes

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