Supramolecular Stabilization of Metastable Tautomers in Solution and the Solid State |
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| Authors: | Dr. Marina Juribašić Nikola Bregović Dr. Vladimir Stilinović Prof. Vladislav Tomišić Prof. Marina Cindrić Dr. Primož Šket Prof. Janez Plavec Dr. Mirta Rubčić Dr. Krunoslav Užarević |
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| Affiliation: | 1. Ru?er Bo?kovi? Institute, Bijeni?ka 54, Zagreb (Croatia), Fax: (+385)?1‐4680‐245;2. Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, Zagreb (Croatia);3. Slovenian NMR Center, National Institute of Chemistry, Hajdrihova 19, Ljubljana (Slovenia);4. EN‐FIST Center of Excellence, Trg OF 13, 1000 Ljubljana (Slovenia);5. Faculty of Chemistry and Chemical Technology, Physical Chemistry, University of Ljubljana, A?ker?eva 5, Ljubljana (Slovenia) |
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| Abstract: | This work presents a successful application of a recently reported supramolecular strategy for stabilization of metastable tautomers in cocrystals to monocomponent, non‐heterocyclic, tautomeric solids. Quantum‐chemical computations and solution studies show that the investigated Schiff base molecule, derived from 3‐methoxysalicylaldehyde and 2‐amino‐3‐hydroxypyridine ( ap ), is far more stable as the enol tautomer. In the solid state, however, in all three obtained polymorphic forms it exists solely as the keto tautomer, in each case stabilized by an unexpected hydrogen‐bonding pattern. Computations have shown that hydrogen bonding of the investigated Schiff base with suitable molecules shifts the tautomeric equilibrium to the less stable keto form. The extremes to which supramolecular stabilization can lead are demonstrated by the two polymorphs of molecular complexes of the Schiff base with ap . The molecules of both constituents of molecular complexes are present as metastable tautomers (keto anion and protonated pyridine, respectively), which stabilize each other through a very strong hydrogen bond. All the obtained solid forms proved stable in various solid‐state and solvent‐mediated methods used to establish their relative thermodynamic stabilities and possible interconversion conditions. |
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| Keywords: | keto– enol metastable compounds Schiff bases supramolecular chemistry tautomerism |
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