Calculations of vapor/liquid equilibrium conditions are done with an extended quasi-chemical model. The lattice-fluid description of the liquid phase includes nonrandomly placed vacancies and interaction parameters using the TraPPE validated force field. Good agreement between experiment and model calculations for binary mixtures of alcohol, alkanes and dimethyl ether is found using two global model parameters and one system-specific interaction scaling parameter. This iteration of the quasi-chemical model performs as well or better than calculations using a published version of Modified UNIFAC and COSMO-SAC-VT-2005 for most of the systems considered. A generalized Guggenheim athermal ways function is derived to model liquid systems with vacancies and predetermined molecular structures. (c) 2007 Elsevier B.V. All rights reserved.