Method for Predicting Dipole Moments of Complex Molecules for Use in Thermophysical Property Estimation

We
present a formalism for accurate estimation of dipole moments
using quantum mechanics for complex molecules having conformational
degrees of freedom. Dipole moments of complex molecules are often
needed for use in correlations for estimating viscosities and other
thermophysical properties. However, experimentally measured dipole
moments are not available for many molecules, especially those used
in proprietary industrial processes and products. Many complex molecules
have dipole moments that change significantly in response to the conformation
of the molecules. We show that proper accounting of the conformation-dependent
dipole moment may be required to achieve an acceptably accurate estimate
of the experimental dipole moment and provide recommendations on efficient
estimation techniques. We also demonstrate that for molecules with
dipole moments above about 1.3 D reasonably accurate estimation of
the dipole moment is required for reliable prediction of vapor phase
viscosity, whereas estimation of thermal conductivity is less sensitive
to the dipole moment.