Nature of the Colored Form

Except for a few cases in which they were exceptionally stable,26 the open-form structures have not yet been determined. Guglielmetti et al26 synthesized the first permanent opened forms of the spiroindolinooxazine compound 27. NMR spectro- 

The calculation indicated that (1) all isomers converged to the planar form (2) the most stable isomer is TTC (3) the electrostatic interaction between the central hydrogen and the oxygen of the carbonyl group contributed to the stability and (4) hydrogen-hydrogen repulsion was the reason for the destabilization of the open form. 

The important bond angles and distances for these open-form isomers are shown in Table 2.9. All C=N bond show a double-bond character, whereas the other 

From the standpoint of application, it is important whether the electronic structure is ketonelike or zwitterioniclike. The calculation results indicate that the C=0 bond distance is in the region of the normal carbonyl length of 1.22 A consequently, the electronic ground state is ketonelike. 

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