Numerical simulations of Liesegang systems are performed both with a prenucleation and a postnucleation
model. Special interest is dedicated to two-dimensional morphological peculiarities of ring systems. With the
prenucleation model, apparent bifurcations or branch points (anastomoses) can be created by adjacent trains
of bands having different interband spaces or band positions shifted to each other. Spiral systems arise when
the circular symmetry of concentric Liesegang rings is broken by at least one branch point. The postnucleation
model comprises both formation of colloidal particles which form a turbidity zone and transition of these
nuclei to solid particles which undergo Ostwald ripening at the expense of the colloids. The model demonstrates
how Liesegang bands of solid particles arise from a primary turbidity zone which surrounds the expanding
ring system. Because of rapid competitive particle growth, rings or bands may no longer grow continuously
in transversal directions. They become arranged in chains of single filaments or spots forming a transversal
rhythm. Finally, longitudinal alleys of gaps appear in continuous trains of Liesegang bands.
Structure Determination of Selected Nitro and Sulfonic Acid Substituted 1,2‐Naphthoquinone‐2‐diazides
Selected nitro derivatives of 1,2‐naphtoquinone‐2‐diazide 2 and 5 have been synthesized, the position of the NO2‐group has been unambigously determined by means of 1H and 13C n.m.r. spectroscopy, and the structure of these compounds has been comprehensively determined in relation to unsubstituted 1 and sulfonic acid substituted derivatives 3, 3a, 4 and 4a.
Furthermore, the spectroscopical behaviour, especially in the uv/vis region, was examined in correlation to quantum chemical calculations.
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