Group electronegativities, which take into account the influence of chemical environment, are calculated. Equilibrium electronegativity is defined on the basis of group electronegativity. Using relative bond lengths and equilibrium electronegativies, we create a novel semiempirical topological descriptor, Nt. A quantitative structure-property relationship (QSPR) model is subsequently developed using Nt together with path numbers P-2 and P-3 to accurately predict thermodynamic properties of organic compounds. Excellent correlation coefficient values demonstrate the accuracy of the method. The contribution analysis indicates that Nt plays the most important role in the modeling. With the new QSPR model, we are able to predict a wide range of thermodynamic properties of an extensive number of molecules. The predictions are provided in the Supporting Information.