Hydrazones from hydroxy naphthaldehydes. Part 2. Condensations with aromatic N-aminoheterocycles and elucidation of tautomeric structures

This paper extends previous studies on hydrazones derived from hydroxyl naphthaldehydes to aromatic N-aminoheterocycles (exemplified herein by triazole derivatives), in an attempt to freeze enamine structures either by altering the electronic properties of the non-iminic nitrogen or through steric hindrance leading to coplanar dispositions between the lone pairs. By comparing experimentally obtained results (NMR in solution and crystal data) to computationally simulated ones (via DFT calculations in the gas phase and CHCl3), the structures of the preferential conformers and tautomers can be confidently assigned. All data are consistent with enhanced stability of imine forms with respect to their enamine counterparts. DFT calculations have the ability to identify the orbital interactions responsible for electron delocalization and the energy of intramolecular hydrogen bonding. In addition, all transition structures for conformational and tautomeric equilibria are located and characterized.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (134 K)Download as PowerPoint slide