The temperature dependence of gas chromatographic retention times for n-heptadecane to n-triacontane is reported. These data are used to evaluate the vaporization enthalpies of these compounds at T = 298.15 K, and a protocol is described that provides vapor pressures of these n-alkanes from T = 298.15 to 575 K. The vapor pressure and vaporization enthalpy results obtained are compared with existing literature data where possible and found to be internally consistent. Sublimation enthalpies for n-C17 to n-C30 are calculated by combining vaporization enthalpies with fusion enthalpies and are compared when possible to direct measurements.

The temperature dependence of gas-chromatographic retention times for hentriacontane to octatriacontane is reported. These data are used in combination with other literature values to evaluate the vaporization enthalpies and vapor pressures of these n-alkanes from T = 298.15 to 575 K. The vapor pressure and vaporization enthalpy results obtained are compared with existing literature data where possible and found to be internally consistent. The vaporization enthalpies and vapor pressures obtained for the n-alkanes are also tested directly and through the use of thermochemical cycles using literature values for several polyaromatic hydrocarbons. Sublimation enthalpies are also calculated for hentriacontane to octatriacontane by combining vaporization enthalpies with temperature adjusted fusion enthalpies.

[reaction: see text] This study is a multinational, multidisciplinary contribution to the thermochemistry of dimethyl1,4-cubanedicarboxylate and the corresponding isomeric, cuneane derivative and provides both structural and thermochemical information regarding the rearrangement of dimethyl 1,4-cubanedicarboxylate to dimethyl 2,6-cuneanedicarboxylate. The enthalpies of formation in the condensed phase at T = 298.15 K of dimethyl 1,4-cubanedicarboxylate (dimethyl pentacyclo[4.2.0.0.(2,5)0.(3,8)0(4,7)]octane-1,4-dicarboxylate) and dimethyl 2,6-cuneanedicarboxylate (dimethyl pentacyclo[3.3.0.0.(2,4)0.(3,7)0(6,8)]octane-2,6-dicarboxylate) have been determined by combustion calorimetry, delta(f) H(o)m (cr)/kJ x mol(-1) = -232.62 +/- 5.84 and -413.02 +/- 5.16, respectively. The enthalpies of sublimation have been evaluated by combining vaporization enthalpies evaluated by correlation-gas chromatography and fusion enthalpies measured by differential scanning calorimetry and adjusted to T = 298.15 K, delta(cr) (g)Hm (298.15 K)/kJ x mol(-1) = 117.2 +/- 3.9 and 106.8 +/- 3.0, respectively. Combination of these two enthalpies resulted in delta(f) H(o)m (g., 298.15 K)/kJ x mol(-1) of -115.4 +/- 7.0 for dimethyl 1,4-cubanedicarboxylate and -306.2 +/- 6.0 for dimethyl 2,6-cuneanedicarboxylate. These measurements, accompanied by quantum chemical calculations, resulted in values of delta(f) Hm (g, 298.15 K) = 613.0 +/- 9.5 kJ x mol(-1) for cubane and 436.4 +/- 8.8 kJ x mol(-1) for cuneane. From these enthalpies of formation, strain enthalpies of 681.0 +/- 9.8 and 504.4 +/- 9.1 kJ x mol(-1) were calculated for cubane and cuneane by means of isodesmic reactions, respectively. Crystals of dimethyl 2,6-cuneanedicarboxylate are disordered; the substitution pattern and structure have been confirmed by determination of the X-ray crystal structure of the corresponding diacid.