Abstract
Lattice energy calculations by semiempirical and quantum mechanical methods have been carried out on 17 crystals of phenoxypropionic acids (PPAs), including 5 pairs of racemic and homochiral partners. Racemic crystals always consist of centrosymmetric cyclic hydrogen-bonded dimers, while homochiral crystals invariably include chain (“catemer”) motifs of O–H···O hydrogen bonds, except for one case having a pseudo-2-fold axis dimer with two molecules in the asymmetric unit. Energy differences between homochiral and racemic crystals are small, without a consistent trend of higher stability of either state. Partitioned molecule–molecule energy calculations show that hydrogen bonds compete with diffuse dispersive factors or local electrostatic interactions. Monte Carlo methods with empirical atom–atom potentials were also applied to simulate the structural and energetic equilibrium properties of some racemic and homochiral liquids. The latter are very nearly isoenergetic, apparently irrespective of molecular s...
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