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The sublimation enthalpies of 17 hydrocarbons are obtained by combining the technique of correlation gas chromatography (CGC), to evaluate vaporization enthalpies at 298.15 K, and differential scanning calorimetry (DSC) to measure fusion enthalpies. Vaporization enthalpies at 298.15 K obtained by CGC are compared to values measured directly from vapor pressure measurements at temperatures above the melting point by adjusting the experimental vaporization enthalpy for the effects of temperature. Vaporization enthalpies obtained by these two methods agree within AE3877 J mol À1 . Fusion enthalpies are similarly adjusted for temperature. Sublimation enthalpies, obtained by combining temperature adjusted fusion, and vaporization enthalpies agree within AE2580 J mol À1. The sublimation enthalpies of azulene and 1,8-cyclotetradecadiyne are also measured by head-space analysis resulting in values of 76880 and 94348 J mol À1 at 298.15 K, respectively. # 1998 Elsevier Science B.V.

The vaporization enthalpies and vapor pressures of 1-, 6-, 7-, and 9-heptadecanol, 1-octadecanol, 1-eicosanol, 1-docosanol, 1-hexacosanol and cholesterol at T = 298.15 K have been measured by correlation gas chromatography using as standards, the even carbon n-alkanols from 1-decanol to 1-octadecanol and 1-pentadecanol. Fusion enthalpies for the all of these compounds were either measured by DSC or obtained from the literature. Adjusted to T = 298.15 K, the fusion and vaporization enthalpies were combined to provide sublimation enthalpies. The sublimation enthalpies were compared to existing literature values. Agreement between the two sets of values when available was generally very good.

The standard (p°) 0.1 MPa) molar enthalpies of formation for 2-, 3-, and 4-phenylpyridine in the gas phase were derived from the standard molar enthalpies of combustion, in oxygen, at 298.15 K, measured by static bomb combustion calorimetry. The standard molar enthalpies of vaporization for 2-, 3-, and 4-phenylpyridine at T) 298.15 K were measured by correlation-gas chromatography. The enthalpy of sublimation of 4-phenylpyridine was obtained as a weighted mean of the value derived from the vaporization and fusion enthalpy values and the value measured directly by Calvet microcalorimetry. The following enthalpies of formation were then derived: 2-phenylpyridine, g) 228.3 (5.8 kJ‚mol-1 ; 3-phenylpyridine, g) 240.9 (5.5 kJ‚mol-1 ; 4-phenylpyridine, g) 240.0 (3.3 kJ‚mol-1. The most stable geometries of all phenylpyridine isomers were obtained using both restricted Hartree-Fock (RHF) and density functional theory (DFT/B3LYP) methods. The resulting geometries were then used to obtain estimates of enthalpies of formation of the three isomers of phenylpyridine, which are in good agreement with the experimental values. A theoretical interpretation of the effect of the phenyl ring has on the relative stabilities of the three molecules is presented.