Applications of double bond indices: Quantitative characterization of properties of benzenoid hydrocarbons
Abstract
Abstract Topological indices (TIs) are widely used descriptors in QSAR/QSPR modeling, but conventional degree-based TIs neglect bond multiplicity, potentially limiting structural resolution. Thirteen extended double-bond-corrected TIs were derived via a Kekuúlé-structure-based edge classification and benchmarked against their conventional counterparts across 100 benzenoid hydrocarbons and 11 physicochemical properties using nested F-tests, FDR-corrected significance testing, and a permutation-based null model to isolate structural contributions from mere numerical continuity. Extended indices resolved substantially more numerical ties than conventional indices (Wilcoxon p = .0010); however, permutation benchmarking showed that this improvement reflects the continuous-valued construction rather than the specific double-bond information encoded (p ≈ 1.00). Regression analyses further showed neither index family exceeded simple size-based baselines (molecular weight, ring count) for most properties, with a marginal exception for log P. This rigorous evaluation clarifies the genuine, more limited scope of double-bond-corrected TIs and establishes a reproducible statistical framework for evaluating future topological descriptors. Graphical AbstractFlowchart detailing methods for deriving extended topological indices from benzenoid hydrocarbons to QSPR analysis.This flowchart outlines a process for deriving extended topological indices from benzenoid hydrocarbons for QSPR analysis. It starts with 26 molecular structures and includes steps for duplicate graph construction and edge weight assignment (single, double, and duplicate bonds). Thirteen indices are derived (e.g., IS_D, M_2RD). QSPR models demonstrate relationships with statistical validation metrics. Lower sections summarize physicochemical properties, regression results, and key outcomes like reduced degeneracy and improved QSPR performance (R^2 up to 0.999).