Molecular Model of Zincon

The Featured Molecules this month are the tautomeric forms of the colorimetric reagent zincon, used in the paper by Maria Mar Areco, Maria dos Santos Afonso, and Erika Valdman on the bioabsorption of zinc, and by extension other metal ions, by seaweed. The structures presented have been calculated at the DFT/6-31G(d) level using the B3LYP functional. These structures represent energy minima, but not necessarily global minima. The structures could be used as an introduction to the concept of tautomerism, with students being asked to develop a definition of the term based on their observations of the difference(s) in linkage in the two forms. An intramolecular hydrogen bond is found in each structure, and introductory chemistry students could be encouraged to look for these structural features in molecules that are more complex than those typically encountered to introduce hydrogen bonding. More advanced students could use computational techniques to explore the energy differences between the two forms, and compare those differences to the ones observed between more traditional keto/enol examples.
Molecular Model of Zincon   
(Interactive Simulation (1))