TAUTOMERISM OF REPRESENTATIVE AROMATIC ALPHA-HYDROXY CARBALDEHYDE ANILS AS STUDIED BY SPECTROSCOPIC METHODS AND AM1 CALCULATIONS - SYNTHESIS OF 10-HYDROXYPHENANTHRENE-9-CARBALDEHYDE

The synthesis of 10-hydroxyphenanthrene-9-carbaldehyde and its anil are described. The structure of the latter compound has been thoroughly studied by H-1 and C-13 NMR, UV-visible absorption, fluorescence and IR spectroscopies. All the experimental results support the existence of this anil mainly in the keto-enamine tautomeric form. A comparison is presented with previously studied anils derived from salicylaldehyde and 2-hydroxynaphthalene-1-carbaldehyde. Semiempirical calculations (AM1) concerning the relative stability of tautomers as well as the optimized molecular geometries are in good agreement with the experimental findings.