Descriptors Based on Additional Information

Molecular descriptors derived solely from D, E, B, and R discriminate between different basic graphs. They do not, however, differentiate between molecules such as I, II, and III with the same basic graph but with differences in their types of atoms, bonds, or stereo- and quantum-chemical features. In the remaining part of this section, a few approaches that extend basic graph descriptors to chemically informed descriptors are introduced. 

The valence-delta value, 6V, is calculated from the atomic electron configuration as follows  

Delta values are used to calculate molecular connectivity indices (MCIs). MCIs are based on numerical quantities assigned to substructures. The substructure quantity is calculated as (6i6j6t 5P) 05 or (6 6J6vk 6p) 0 5, where the multiplication of delta values is carried over all atoms that belong to the particular substructure. Four different substructure types have been applied path (P), cluster (C), path-cluster (PC), and chain (CH). The number of bonds present in a given substructure is called the order of the substructure. A specific MCI is defined as the sum of all substructure quantities considering a substructure of a particular type and a particular order. The 

MCI symbol is x, specified by a left-side superscript representing the order, by a right-side superscript v if the MCI is based on 6V values, and by a right-side subscript representing the substructure type. If no subscript is indicated, type P is assumed. For example, the MCI x, defined in eq. 2.3.12, is derived from 6 values. It is a P-type index of order 1. The analogous valence-corrected MCI, 1xv, is defined as 

Subsequent definitions are given for 5-derived MCIs. Corresponding valence- 

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