Enthalpies of Vaporization and Vapor Pressures of Some Deuterated Hydrocarbons. Liquid−Vapor Pressure Isotope Effects

Abstract

Liquid-vapor pressures as a function of temperature and enthalpies of vaporization of a series of both liquid and solid hydrocarbons and their perdeuterated analogues have been determined by correlation-gas chromatography. The applicability of this technique is first demonstrated by reproducing the vapor pressure isotope effect of cyclohexane-d 12 and benzene-d 6 . Other hydrocarbons studied include the perdeuterated forms of hexane, toluene, heptane, the p-and o-xylenes, naphthalene, biphenyl, acenaphthene, phenanthrene, anthracene, hexamethylbenzene, p-terphenyl, perylene, and chrysene. Vapor pressures and vaporization enthalpies of unlabeled hexamethylbenzene and perylene are also reported. Inverse vapor pressure isotope effects of the liquid phase are observed for all the substances examined. Vaporization enthalpy differences between unlabeled and labeled hydrocarbons are small and generally slightly positive. Vapor pressure-temperature relationships are reported in the form of a third-order polynomial that appears to reproduce experimental liquid-vapor pressures from T ) 298.15 K to the boiling temperature.

An examination of the vaporization enthalpies and vapor pressures of pyrazine, pyrimidine, pyridazine, and 1,3,5-triazine

“…Vapor pressures for 2-methylpyrazine [7], 2,5-dimethylpyrazine [7], and 2,4,6-trimethylpyridine [7] were obtained from the original article and fit to a third-order polynomial, Eq. 8, known to provide reasonable vapor pressure values upon extrapolation [5,15].…”

Gas-Phase Reaction of Hydroxyl Radical with Hexamethylbenzene

“…In this study, we used both OH and OD radicals, as the use of isotopologues allows us to clarify some fragmentation patterns, thereby allowing us to distinguish the PMBOD + ion arising from the minor OD + PMB secondary reaction from the fragment HMB−OD + -H, both having the same mass. Because of experimental difficulties to obtain large concentrations of HMB in the gas-phase (its vapor pressure at 298 K being equal to 12 mTorr), 39 HMB was introduced in excess by only a factor of 10 to 30 with respect to the initial OH concentration. Therefore, the (HMB + OH ⇆ HMB−OH) equilibrium, established quickly, was not always fully shifted toward the adduct and the stationary OH concentration was not always negligible, particularly at high temperatures, leading to potential OH induced secondary reactions.…”

Gas Chromatography-Mass Spectrometric Studies of O-Alkyl O-2-(N,N-Dialkylamino) Ethyl Alkylphosphonites(Phosphonates) for Chemical Weapons Convention Verification

“…21 For most unlabeled and labeled compounds, inverse vapor pressure isotope effects have generally been seen, p D > p H . 22 In this study, the RI values of labeled compounds are less than unlabeled compounds (Table 1).…”