Pigment Violet angular structure

Traditionally, the product has been assumed to possess the linear molecular structure 4. However, comparison of the commercial product to one synthesized specifically to adopt the linear structure exhibited differences between their respective visible spectra and other physical properties. Although speculative at that time, the data did imply the possibility that the actual molecular structure of Pigment Violet 23 was represented better by the S configuration resulting from angular ring fusion. 

More recently, it has been demonstrated unequivocally, by single crystal X-ray diffraction analysis, that the molecular structure of Pigment Violet 23 does possess the angular configuration 3, the result of an A-E fusion. In conjunction with that same research it has been demonstrated also that the linear structure affords a blue shade product that apparently has no commercial importance as a pigment. 

Of special note is the linear structure of the resulting molecules (Figure 20-16), unlike the angular structure of Pigment Violet 23, as confirmed by NMR. This is perhaps due to the known higher reactivities of the 5 and 6 positions of the benzimi-dazolone molecule. 

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