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The variable Zagreb (v)M(2) index is introduced and applied to the structure-boiling point modeling of benzenoid hydrocarbons. The linear model obtained (the standard error of estimate for the fit model S(fit)=6.8 degrees C) is much better than the corresponding model based on the original Zagreb M2 index (S(fit)=16.4 degrees C). Surprisingly,the model based on the variable vertex-connectivity index (S(fit)=6.8 degrees C) is comparable to the model based on (v)M2 index. A comparative study with models based on the vertex-connectivity index, edge-connectivity index and several distance indices favours models based on the variable Zagreb (v)M2 index and variable vertex-connectivity index.However, the multivariate regression with two-, three- and four-descriptors gives improved models, the best being the model with four-descriptors (but (v)M2 index is not among them) with S(fit)=5 degrees C, though the four-descriptor model contaning (v)M2 index is only slightly inferior (S(fit)=5.3 degrees C).

published in Advance ACS Abstracts, November 1, 1995. 0095-233819511635-1034$09.00/0 0 ing various combinations of molecular descriptors. The structures of the flavone derivatives used in this study are shown in Figure 1. A total of 34 descriptors were generated for each flavone derivative. The descriptor pool contained topological and electronic descriptors. The topological descriptors that were calculated include valence connectivity indexes6 0f”’5xv, Wiener number Wand path numbers7 pO-plo, Balaban indexs J, Harary indexes9 HI -&, and molecular topological indexi0 MTI. The electronic descriptors include hardness indexes’ ’ (absolute hardness r, relative hardness qr), energy of the highest occupied molecular orbital E(HOMO), and energy of the lowest unoccupied molecular orbital E(LUMO), topological resonance energy indices’ (topological resonance energy TRE and topological resonance energy per electron TRE(PE)), and the sum of the charges of the atoms located in the chromone moiety

published in Advance ACS Abstracts, November 1, 1995. 0095-233819511635-1034$09.00/0 0 ing various combinations of molecular descriptors. The structures of the flavone derivatives used in this study are shown in Figure 1. A total of 34 descriptors were generated for each flavone derivative. The descriptor pool contained topological and electronic descriptors. The topological descriptors that were calculated include valence connectivity indexes6 0f”’5xv, Wiener number Wand path numbers7 pO-plo, Balaban indexs J, Harary indexes9 HI -&, and molecular topological indexi0 MTI. The electronic descriptors include hardness indexes’ ’ (absolute hardness r, relative hardness qr), energy of the highest occupied molecular orbital E(HOMO), and energy of the lowest unoccupied molecular orbital E(LUMO), topological resonance energy indices’ (topological resonance energy TRE and topological resonance energy per electron TRE(PE)), and the sum of the charges of the atoms located in the chromone moiety

A novel multivariate linear regression, based on the ordered orthogonalized connectivity basis and dominant descriptor analysis, is applied to several physicochemical properties of α-amino acids. Our results compare favourably with those based on the non-orthogonalized connectivity basis by Pogliani.

This report presents the best possible QSPR models for predicting the solubility of aliphatic alcohols in water that can be obtained with non-orthogonalized valence-connectivity basis. The corresponding models with orthogonalized basis, ordered in the usual manner, are also given. However, both models are statistically equivalent. Therefore, we proposed a novel approach to the QSPR modelling, which is based on the consideration of all possible or- thogonalization orderings of the valence-connectivity basis and dominant descriptor analysis. This novel procedure produced models that are better than the empirical models of Amidon et al. and the Kier-Hall models when considering the same source of experimental data.

An application of the molecular topological index, adapted for heterosystems, in the QSAR study of toxicity of alkyl alcohols on fathead minnows (Pimephates promelas) is examined. The obtained QSAR model is comparable to models based on the Wiener number and the connectivity index.

The topological resonance energy (TRE) model was used to study the aromatic stability of cationic AH+ and anhydrobase from A of the flavylium chromophoric system. The calculated values of TRE are within the regular limits for the aromatic molecules, with the cationic forms being more aromatic than the anhydrobase forms. Higher stability of 4-CH3 flavylium salts is expected relative to 4-H flavylium salts.

Topological resonance energies of thiocoumarin, thiochromone, and related systems are reported. Theoretical predictions indicate that systems in which the benzene ring retains to great extent its aromatic structure are much more stable than the corresponding . quinonoid isomers.

The aromatic stabilities of bridged polyenes have been studied by means of the topological (graph-theoretical) resonance energy (TRE) model developed by the Zagreb Group a decade ago. The aromatic stabilities of bridged polyenes are compared with those predicted earlier for polyenes, annulenes, bridged annulenes, and polyacenes. This comparison has produced the following aromatic stability order: polyenes < annulenes < bridged polyenes < bridged annulenes < polyacenes. The available experimental findings support this prediction.

The aromatic stabilities of isomeric azulenofurans, azulenopyrroles and azulenothiophenes have been studied by three theoretical models of aromaticity: the graphical model, the conjugated circuits model and the topological resonance energy model. All three models predict that molecules with the delocalized underlying carbon structure are more stable than those with the quinoid structure. In each class of positional isomers, azulenopyrroles are always predicted to be more stable than the corresponding isomeric azulenothiophenes, and these more stable than the corresponding azulenofurans. However, all azulenofurans, azulenopyrroles and azulenothiophenes are predicted to be less aromatic than the parent hydrocarbon 2, 3-benzazulene. It is suggested that the differences in stability between azulenofurans, azulenopyrroles and azulenothiophenei is related to the differences in stability between the heterocyclic parts of the molecules, i.e. furan, pyrrole and thiophene, since the carbon parts are identical.