On use of the variable Zagreb vM2 index in QSPR: boiling points of benzenoid hydrocarbons.

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).