Delocalisation indices

A delocalisation index can be calcvJated between any two atoms in a molecule, a complex, or a crystal, whether these two atoms are bonded or not. When S(A,B) is calculated for two bonded atoms it is a measure of the bond order between them [111, 112], Since pj and the BO are strongly correlated (Eq. 4), Matta and Hernandez-Trujillo suggested to calibrate this correlation using the delocalisation index rather than arbitrarily assigned bond orders [113] ... 

The definition of the delocalisation index DI in [8S] is confusing due to the lack of a final and explicit formula for DI and because of scattering important technical information in the paper s main text. Fortunately, the numerical values reported in that paper for DI are in line with values published elsewhere. 

The bond order, as a delocalisation index, measures the number of electron pairs shared between topological atom A and B. This index can be linked to the fluctuation of the electron population, denoted N, in both atoms. 

Most of these products are azo or anthraquinone types, often with a localised quaternary ammonium group isolated from the chromogen by a saturated alkyl chain, as in Cl Basic Red 18 (1.52). Such products often exhibit higher light fastness than the traditional delocalised types. Improved azomethine, methine and polymethine basic dyes of good light fastness are also available. In contrast to the more specialised traditional classes, the azo and methine dyes have contributed to the basic dye range across the entire spectrum of hues (see Table 1.6) and now account for a clear majority of all basic dyes listed in the Colour Index. 

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