Molecular modeling of isomer effects in naphthenic and aromatic hydrocarbons

In general, the vapor pressure is correlated to 10% average absolute deviation (%AAD) and the liquid density to 4%AAD. These are slightly larger than the errors encountered in characterizing straight chain hydrocarbons, ethers, and alcohols. One complicating factor that may explain the larger errors in this instance is the subtle variability in molecular structure caused by the consideration of isomers with branching in different positions around the ring. The transferable potentials account for this variability in a configurational sense, but not in a quantum mechanical sense. A detailed study reveals the extent to which the vapor pressure of several isomers can be correlated qualitatively and quantitatively. A preliminary study suggests one manner in which quantum mechanical corrections can be implemented.