Design of Topological Indices. Part 10. Parameters Based on Electronegativity and Covalent Radius for the Computation of Molecular Graph Descriptors for Heteroatom-Containing Molecules

Abstract

Two new approaches are presented for the calculation of atom and bond parameters for heteroatom-containing molecules used in computing graph theoretic invariants. In the first approach, the atom and bond weights are computed on the basis of relative atomic electronegativity, using carbon as standard. In the second system, the relative covalent radii are used to compute atom and bond weights, again with the carbon atom as standard. The new definition of the atom and bond parameters leads to a periodic variation versus the atomic number Z, with a more natural variation when compared with the parameters defined only by Z. The two approaches are used to define and compute topological indices based on graph distance. A quantitative structure−property relationship study is reported for boiling points of 185 acyclic compounds with one or two oxygen or sulfur atoms (devoid of hydrogen bonding), in terms of four or five molecular descriptors.

Can topological indices transmit information on properties but not on structures?

“…Then, the result replaces the distance sum for that vertex. Bond parameters are computed by weighting schemes in terms of bond multiplicity and of either the relative electronegativity or the relative covalent radii of the two atoms involved in the bond [33,34]. An interesting observation is that index J orders alkanes like index W, [35,36] and also similarly to Bertz's line-graph-derived descriptor [37].…”

Variable Connectivity Index as a Tool for Modeling Structure-Property Relationships

“…Hence, we introduced two variables, variable x to modify the weights of the carbon atoms and variable y to modify the role of the oxygen atom. After a search for the optimal values for the two variables, we obtain a standard error and coefficient of regression of s = 89.9°C and r = 0.133, respectively, with x = 2 and y = 10 15 . Thus, clearly the variable connectivity index, while having the flexibility to adjust to specific structural variations of molecules (alcohols), cannot adjust to fit random data.…”

“…Examples include the well-known valence connectivity indices of Kier and Hall [8,9], which are derived from the connectivity index [10] and the "higher order" connectivity indices [11], descriptors derived from distance matrix of molecules containing heteroatoms [12], Balaban's topological index J for heteroatom-containing molecules [13][14][15] derived from the topological index J [16], Zefirov and Palyulin's "solvation connectivity index" [17][18][19]. We will see later how the variable connectivity index may be viewed not merely as a generalization of the "valence" connectivity indices but as an "unlimited" collection of "valence" connectivity indices.…”

Identification of Groupings of Graph Theoretical Molecular Descriptors Using a Hybrid Cluster Analysis Approach

“…20 To compute graph structural descriptors, several weighting schemes were proposed by using the atomic number Z, 48 the atomic radius, and electronegativity. 47,49 The molecular descriptors used in this paper were computed with six weighting schemes w, namely, the atomic number Z, the atomic mass A, the hydrogen-augmented atomic mass AH, the atomic polarizability P, the atomic electronegativity E, and the atomic radius R. 50 The theory and calculation of these descriptors has been described in detail elsewhere. 35 (7) the Hosoya indices computed with the Hosoya operator Ho(A,w).…”