Molecular Recognition and Shape Studies of 3- and 4-Substituted Diarylamide Quasiracemates

Abstract

Families of quasiracemic materials constructed from 3- and 4-substituted chiral diarylamide molecular frameworks were prepared, where the imposed functional group differences systematically varied from H to CF3–9 unique components for each isomeric framework. Cocrystallization from the melt via hot stage thermomicroscopy using all possible racemic and quasiracemic combinations probed the structural boundaries of quasiracemate formation. The crystal structures and lattice energies (differential scanning calorimetry and lattice energy calculations) for many of these systems showed that quasienantiomeric components organize with near inversion symmetry and lattice energetics closely resembling those found in the racemic counterparts. This study also compared the shape space of pairs of quasienantiomers using an in silico alignment-based method to approximate the differences in molecular shape and provide a diagnostic tool for quasiracemate prediction. Comparing these results to our recent report on related 2-substituted diarylamide quasiracemates shows that functional group position can have a marked effect on quasiracemic behavior and provide critical insight to a more complete shape space, essential for defining molecular recognition processes.