Univariate Prediction\nof Hammett Parameters and Select\nRelative Reaction Rates Using Loewdin Atomic Charges

Loewdin charges from density functional theory calculations\nwere\nused here to obtain general, univariate linear correlations for the\nprediction of experimental Hammett parameters and relative reaction\nrates. While previous studies have established that Hirshfeld and\nCM5 charges perform strongly as univariate predictors, the near-ubiquitous\nLoewdin charges have not yet been evaluated. To this end, we assess\nthe predictive capability of Loewdin charges for three chemical systems.\nFirst, we show that Loewdin charges outperform Hirshfeld and CM5 charges\nfor Hammett parameter prediction. Second, we see that Loewdin charges\ngenerally perform comparably to Hirshfeld charges for predicting the\nrelative rates of olefin cleavage by photoexcited nitroarenes. The\nsingle case of poor correlation, between relative rates and the Loewdin\ncharges on nitrogen sites, is ameliorated when considering the net\ncharge on the NO<sub>2</sub> group. Third, we show that Loewdin, Hirshfeld,\nand CM5 charges all perform very well for generating correlations\nfor relative reaction rates for C–H activation of 9-(4-X-phenyl)-9<i>H</i>-fluorene substrates by a transition metal catalyst. The\nequations generated throughout the study enable the prediction of\nHammett parameters and relative reaction rates. These tools can accelerate\nsynthetic and experimental studies by enabling the in silico prediction\nof uncharacterized chemical properties.