MO-LCAO calculations on polymethines: XXIII-the origin of the absorption colour of dithizone and related compounds

Spectroscopic and quantum chemical study on electronic and geometric properties of free and embedded dithizone molecules

“…In solution, on the other hand, the appearance of the tautomeric enol and keto forms (Fig. 1) have also been suggested 2–4. While the geometries of about 20 conformers may be discussed, just a few isomers will significantly be stabilized by the extended π electrons and by intramolecular hydrogen bonding as illustrated, for example, in Figure 1.…”

“…For example, the traditional view expects a tautomeric equilibrium for dissolved dithizone between the enol form (b: PhNHNC(SH) NNPh) and the keto form (c: PhNHNHCSNNPh) 2. Fabian et al 4 have found arguments for the appearance of the symmetrical ( C 2 v ) form (a: PhNHNCSNNHPh) by comparing MO–LCAO calculations with results from nuclear magnetic resonance (NMR) and X‐ray investigations. On the other hand, Hutton, who published a series of articles in this field, has argued that only a single molecular species should appear when dissolved in chloroform, benzene, or acetone 5.…”

Synthesis, absorption spectra and semiempiric calculations on the photochromism of arylmercuric dithizonate complexes

“…However, the nature of excited electronic states as well as the underlying molecular structure is still controversially discussed. While the traditional view expects for dissolved dithizone a tautomeric equilibrium between the keto form (a) (Ph−NH−NH−CS−N=N−Ph) and the enol form (b) (Ph−NH−N=C(SH)−N=N−Ph) [1], Hutton [2] and Fabian [3] have found arguments also for the appearance of the symmetrical (C 2v ) form (c)(Ph−NH−N−CS−N−NH−Ph). In a recent theoretical investigation we have addressed the question of stability and molecular geometry to the variety of possible conformers of the three tautomeric forms and have compared the calculations with new findings from low-temperature optical and high-resolution (500 MHz) NMR experiments [4,5].…”