A novel index EDm based on ionicity index matrix, improved distance matrix, and branching degree matrix is used to describe the structural information of the molecule and realizes unique characterization of the molecular structures. The quantitative structure-property relationship (QSPR) models, with correlation coefficients (R) in the range of 0.99-1.00 for standard enthalpy of formation (∆ f H θ m ), standard entropy (S θ m ), molar volume (Vm), and molar refraction (Rm) of alkanes, alkenes, and alkynes, are subsequently developed using the index EDm. The leave-one-out (LOO) method and random sampling prediction (RSP) method demonstrate the models to be statistically significant and reliable. Compared with other published topological descriptors, the index EDm has many advantages such as zero degeneracy, better simulation, and so on. Furthermore, the models of solubility and octanol-water partition coefficient are built with satisfied results, which further manifests the superiority and wide application of this index.

In this paper, we find that stretching vibration frequencies of the X=O for series of R 1 R 2 C=O, (RO) 2 CO, RCO 2 H, α-halogenated aldehydes, cross-RONO and R 2 NNO can be described by the ionicity indices of X and O atoms as follows: υ = aINI (O) +bINI (X) +c, where a, b, c are regression constants, and INI (X) , INI (O) represent the ionicity indices of X and O atoms. The efficiency of the model is verified by high correlation coefficients in the range of 0.960-1.000. Similarly, the ultraviolet absorption energy of ketones can also be characterized by the ionicity indices of C and O as ΔE = aINI (O) +bINI (C) +c. The predicted results are in good agreement with the experimental ones. Furthermore, the good stability and powerful predictive ability of those models are proved by LOO method.

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In this paper, on the basis of the topological index ED m derived from ionicity index matrix, improved distance matrix and branching degree matrix, we proposed the new topological descriptor ED m ΄ by introducing the bond angle into hidden hydrogen graph of molecules and using the geometric distance instead of the sum of bond length between two vertexes. The ED m ΄ describes the molecular structure more accurately, and realizes unique characterization to cis-trans isomers. The quantitative structure-property relationship (QSPR) models, with correlation coefficients (R) in the range of 0.984-1.000 for the boiling point (b.p.), the standard enthalpy of formation ( D f H m θ ), the molar refraction (R m ) and the molar volume (V m ) of some cis-trans isomers for alkenes, are subsequently developed by index ED m ΄. Moreover, the good stability and predictive ability of the models were demonstrated by LOO (leave-one-out) method and RSP (random sampling prediction) method, which further manifests the index ED m ΄ has high potential of wide applications in QSPR study.

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