WHY HYDROGEN-BONDED LIQUIDS TEND TO HAVE HIGH STATIC DIELECTRIC-CONSTANTS

We demonstrate that hydrogen-bonded liquids tend to have higher static dielectric constants than dipolar aprotic liquids, when the two are compared at the same value of the dipolar strenght function y (=(4pi/9)mu2rho/kT). We use a recently developed perturbation theory to show that this is at least partially due to a high ratio of the dipole/quadrupole moment that characterizes molecules which can hydrogen-bond. Depending on this ratio, we can reproduce approximately the experimental dielectric constant behavior of either hydrogen-bonded or dipolar aprotic liquids. We also find that for both purely dipolar and for water-like liquids, correlations due to direct interactions between pairs of molecules (e.g., nearest-neighbor interactions) contribute much less to the underlying dipolar angular correlation function than do the pair correlations due to indirect interactions.