Metastable Zone Widths, Conformational Multiplicity, and Seeding

The propensity for crystallisation of acetanilides and propionanilides was compared both by polythermal metastable zone width measurements and by isothermal induction time measurements. Although there were clear relationships between the metastable zone widths and the conformational multiplicity in some cases, they broke down for the chloroacylanilides. This failure could not be fully accounted for by the difference in the crystal structures of the chloro compounds. A surprising dependence of crystal size on seeding effectiveness could explain some of the crystallisation behaviour, particularly for the induction period measurements.