engleski

On variable Wiener index

A variable Wiener index W-nu, applicable only to acyclic structures, is defined as Sigma [n(1)(e) n(2)(e)](lambda). For the optimal exponent, that value of lambda should be selected which gives the smallest standard error of estimate, s, in the structure-property-modeling. As a test case, the structure-boiling point modeling of isomeric octanes is used. It is found that the optimal exponent is lambda=1/3 which gives a two-parameter model with the lowest value of s (0.72 degreesC) of all tested models. Close to this model is a two-parameter model based on the variable Wiener index with exponent lambda=-1/3 (s=0.83 degreesC). Among the published models, only four- and five-parameter models, based on the overall connectivity indices, produce lower values of s (0.71 degreesC, 0.55 degreesC).

graph valence-shells; topological indexes; molecular connectivity; distance matrix; Harary index; trees; descriptors; numbers

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