ENTHALPIES OF VAPORIZATION OF SOME HIGHLY BRANCHED HYDROCARBONS

Measurements of the molar enthalpy of vaporization Delta(vap)H(m) at the temperature T = 298.15 K are reported for 14 liquids and 6 solids each containing one or more quaternary carbon atoms, by the methods of transpiration, head-space analysis, or gas chromatography. The results are compared with literature values and with estimates based on a simple two-parameter equation developed previously for hydrocarbons. A relation between the solvent-accessible surface area A and the value of Delta(vap)H(m) has been observed for hydrocarbons containing quaternary centers. Measurements of the molar enthalpies of sublimation Delta(sub)H(m) are also reported for two more solids at T = 293 K or at T = 298.15 K.