Prediction of standard absolute entropies for gaseous organic compounds

To predict the standard absolute entropies of gaseous organic compounds, the variable molecular connectivity index (mχk″) and Ring parameter (H), based on the adjacency matrix of molecular graphs, the variable atomic valence connectivity index (δi″), and the numbers of chain (cycle) atom of a molecule (niR) were proposed. The δi″, mχk″ and H are defined as: δi″ = c·(Ziv − hi)·mi·2.89a/(Zi − Ziv + 0.89)a, χkm"=∑j=1nm(∏i=1m+1δi'')j−y, and H = (ln(1.29 + 0.31niR))2.4. The optimal values of the parameters c, a, mi, and y included in definition of the δi″ and mχk″ can be found by the optimization method. The result shows that the definition of the δi″, for a skeletal atom, expresses both electronic and topological information, and can reflect the different chemical environment of the given atom. A four-parameter model can be constructed from the H and mχk″ by using the best subset regression analysis method and the model could be used to predict the standard absolute entropies of gaseous organic compounds accurately.

► Variable atomic valence connectivity index δi″ and Ring parameter H were proposed.
► A variable molecular connectivity index mχk” was constructed.
► A good four-parameter model can be constructed from H and mχk” by the MLR method.
► The model can be used to predict the standard absolute entropies accurately.