Prediction of standard absolute entropies for gaseous organic compounds

To predict the standard absolute entropies of gaseous organic compounds, the variable molecular connectivity index ((m)chi(k)'') and Ring parameter (H), based on the adjacency matrix of molecular graphs, the variable atomic valence connectivity index (delta(i)''), and the numbers of chain (cycle) atom of a molecule (n(i)(R)) were proposed. The delta(i)'', (m)chi(k)'' and H are defined as: delta(i)'' = c (Z(i)(v) - h(i)) m(i) 2.89(a)/(Z(i) - Z(i)(v) + 0.89)(a), (m)chi(k)'' = Sigma(nm)(j=1) (Pi(m+1)(i=1)delta(i)'')(j)(-y), and H = (ln(1.29 + 0.31n(i)(R)))(2.4). The optimal values of the parameters c, a, m(i), and y included in definition of the delta(i)'' and (m)chi(k)'' can be found by the optimization method. The result shows that the definition of the delta(i)'', 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 (m)chi(k)'' 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. (c) 2012 Elsevier B.V. All rights reserved.