Colour and Molecular Structure

Table 2.4 shows a comparison of experimental and PPP-MO calculated electronic spectral data for azobenzene and the three isomeric monoamino derivatives. Notably, the ortho isomer is observed to be most bathochromic, while the para isomer is least bathochromic. From a consideration of the principles of the application of the valence bond approach to the relationship between colour and molecular structure described in the previous section of this chapter, it might have been expected that the ortho and para isomers would be most bathochromic with the meta isomer least bathochromic. In contrast, the data contained in the table demonstrate that the PPP... 

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