Valence connectivity indices

The definition of the valence connectivity indices is related closely to the definition of simple ( ) and valence (I I) value. In the molecular connectivity formalism ... 

Differential connectivity indices are defined as differences between connectivity indices "x d -> valence connectivity indices [Hall and Kier, 1986 Kier and Hall, 1991] ... 

In general, values of c < 5 were assumed. The chirality correction was also applied to valence vertex degrees from which valence connectivity indices are derived. 

To account for nondispersive force effects, the relative valence connectivity indices to nonpolar compounds were defined as... 

By replacing the vertex degree 5 by the —> valence vertex degree 5 in the formulas reported above, similar valence connectivity indices were proposed [Kier and Hall, 1981,1983b], denoted by able to account for the presence of heteroatoms in the molecule as well as double and triple bonds (Table C6). 

Table C7 Some connectivity and valence connectivity indices for the data set of phenethylamines (Appendix C- Set 2).

As shown in figures 2.5-2.8, the zeroth-order and first-order connectivity indices correlate quite strongly with N, and thus also with each other. The correlations of N with the valence connectivity indices °%v and are both much weaker than the correlations of N with x and... 

As mentioned in a footnote to Table 2.1, the use of 8v=l/3 or 8v=4/9 for silicon atoms, as obtained from the definition of 8V (Equation 2.1), causes the overestimation of the effect of the extra inner shell of electrons in silicon atoms on certain physical properties. Whenever this happens, the replacement Si—>C (i.e., 8V=3 or 4) will be made in calculating the valence connectivity indices to correlate that property. For such properties, the differences between Si and C atoms will be taken into account by introducing an atomic correction term for the number of silicon atoms in the repeat unit. The alternative sets of °%v and values obtained for silicon-containing polymers by making the replacement Si—>C in the hydrogen-suppressed graph of the polymeric repeat unit, are listed in Table 2.3. 

Cl model The methodology proposed by Gani et al. [18] permits the creation of missing groups and the prediction of their contribution by using valence connectivity indices Cx) described by Kier and Hall [60]. The property model equation is given by the following equation ... 

Over the past almost four decades, the connectivity index has received considerable attention. For most of its early recognition, clear responsibility goes to Kier and Hall [16,17], who were very much interested in both structure-property and structure-activity studies. Besides hydrocarbons, they paid attention to compounds involving oxygen, nitrogen, fluorine, chlorine, bromine, sulfur, and more. Kier and Hall immediately realized a need to differentiate among atoms of different kinds, which brought them to formulate a modification of the connectivity index known as the valence connectivity indices [18], which, from the start in 1976, have continued to play an important role in QSAR even today. 

The valence connectivity indices not only represent, strictly speaking, an ad hoc solution for discrimination of heteroatoms, even if plausible, but indirectly presume that there are universal valence weights characteristic for individual heteroatoms and valid for all their molecular properties. That the latter assumption is questionable follows from the already mentioned few regression equations of Kier and Hall in which the classical connectivity index x produced better correlations than the corresponding valence connectivity index. Recognition that different molecular properties may require different heteroatom weights led to the idea of the variable connectivity index. 

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