MATERIALS SCIENCE OF ORGANIC-COMPOUNDS .3. GLASS-FORMERS, VITRIPHORES, T(G), AND MOLECULAR CHIRALITY

Non-centrosymmetric crystals are required for second-harmonic generati on (SHG). Homochiral compounds cannot crystallize centrosymmetrically. Various chiral p-nitrophenylurethanes and ureas, useful for SHG, were studied by differential scanning calorimetry (DSC). On quench-cooling from the melt, these compounds invariably formed glasses and gave T-g values on reheating. This behavior was generalized, first to other ho mochiral compounds, and then to racemic mixtures. For mixtures the T-g values were not strictly linear interpolations. The rule is proposed that molecular chirality, even when of steric origin and/or rapidly in verting, strongly favors glass formation. An attached dissymmetric gro up is termed a ''vitriphore''.