On Topological Indices, Boiling Points, and Cycloalkanes

The experimental boiling points (bp) of saturated hydrocarbons (acyclic through polycyclic) up to decanes are systematically compiled. The bp values are classified into groups of lower or higher reliability according to the accuracy and frequency with which they were reproduced by independent researchers. For each hydrocarbon structure the values of several simple topological indices (TI) of widely varying origin are given, including the values of molecular walk counts of various lengths and their sum. The sensitivity of the TIs for structural changes within comprehensive groups of cyclic saturated hydrocarbons is evaluated, and the total walk count is found to be most sensitive. By multilinear regression structure−bp correlations are obtained for various comprehensive compound samples. Both the detour index and the walk counts are found to play a major role in the best models. Comparison of the bp models obtained with those from the recent literature reveals significant improvements for both cyclic and acyclic alkanes, which is attributed in part to the higher quality of experimental data, in part to the use of novel descriptors, and in part to the use of a more diverse pool of descriptors to select from. Despite this a descriptor combination allowing to accurately model cycloalkane bps is not yet found.