The impact of molecular shape and polarity on chiral discrimination

The structure in eighteen racemates is explored at three temperatures and t hree densities. The enantiomers vary in shape from elongated, to nearly sph erical, to flattened. Discrimination, as measured by the difference between like-like (LL) and like-unlike (LU) radial distributions, is assessed for these racemates. Elongated molecules show discrimination most readily with differences of up to 25% between the LL and LU distributions. However, the magnitude depends strongly on the orientation of the molecular dipole. Flat tened molecules also show some discrimination but the magnitude is always q uite small. The fluid structure is obtained from the molecule-based hyperne tted chain theory (HNC) which has been applied, for the first time, to race mates. The incorporation of chirality into HNC theory is nontrivial. Specif ically, for racemates, the number of nonzero coefficients in the rotational invariant expansions is very large, each coefficient is complex, and caref ul treatment of molecular shape into the closure relation is required. Our numerical procedures are discussed in detail. Bridge diagrams have also bee n evaluated for a reference system of hard ellipsoids. The impact of inclus ion of these bridge diagrams has been considered for one racemate and found to be small. (C) 2001 American Institute of Physics.