Abstract
The structural features of octane isomers were quantified with help of the Structural Numbers. A Mutually Optimized Contribution of the Structural Numbers (MOCSN) was used to calculate which parts of information regarding branching contribute the tested Structural Numbers. Besides the known Structural Numbers, two Asymmetry Numbers were developed in order to quantify the asymmetry of the octane isomers, one regarding the asymmetry along the main chain of the molecule and the other one regarding the asymmetry perpendicular to the main chain of the molecule. Their correlation to the values of 29 tested physicochemical properties of octanes was low, |R| < 0.6. After optimization of the Mutually Optimized Contribution of the Structural Numbers, the Information Content of the Mutually Optimized Contribution of the Structural Numbers ranged from 34.3% to 89.0% of the information contained in the physicochemical properties. The Structural Numbers enable the first step of the structural interpretation of physicochemical properties of octane isomers. In 17 out of 29 cases the most of information contained in the physicochemical properties is presented among the Structural Numbers by the Number of Branches, in 8 cases by the Peripheral Number, in 3 cases by an Asymmetry Number and in 1 case by the Distance Number.
Highlights
In order to estimate the unknown values of the physicochemical properties (PCP) of alkanes, Wiener[1] started the development of the numerical measures of their structure, later named the topological indices.[2,3] In the structure of alkanes, the branching of their molecules is obvious
Besides the known Structural Numbers, two Asymmetry Numbers were developed in order to quantify the asymmetry of the octane isomers, one regarding the asymmetry along the main chain of the molecule and the other one regarding the asymmetry perpendicular to the main chain of the molecule
After optimization of the Mutually Optimized Contribution of the Structural Numbers, the Information Content of the Mutually Optimized Contribution of the Structural Numbers ranged from 34.3% to 89.0% of the information contained in the physicochemical properties
Summary
In order to estimate the unknown values of the physicochemical properties (PCP) of alkanes, Wiener[1] started the development of the numerical measures of their structure, later named the topological indices.[2,3] In the structure of alkanes, the branching of their molecules is obvious. It comprises several structural variables, for example the number of branches, their valencies, their distances apart, their distance from the graph center, the lengths of branches, etc.[4] any definition of branching must rest on an intuitive basis.[5] Bonchev and Trinajstić[6] presented several rules representing branching. To test the importance of symmetry of octanes regarding their physicochemical properties (PCP) in a different way, in present paper two measures of symmetry of octane molecules, i.e two Asymmetry Numbers were developed. They were tested alone as well as in combination with other Structural Numbers. For other groups of alkanes, the Structural Numbers of them are to be derived and used using the approach described below
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