Univariate Prediction of Hammett Parameters and Select Relative Reaction Rates Using Loewdin Atomic Charges

Loewdin charges from density functional theory calculations
were
used here to obtain general, univariate linear correlations for the
prediction of experimental Hammett parameters and relative reaction
rates. While previous studies have established that Hirshfeld and
CM5 charges perform strongly as univariate predictors, the near-ubiquitous
Loewdin charges have not yet been evaluated. To this end, we assess
the predictive capability of Loewdin charges for three chemical systems.
First, we show that Loewdin charges outperform Hirshfeld and CM5 charges
for Hammett parameter prediction. Second, we see that Loewdin charges
generally perform comparably to Hirshfeld charges for predicting the
relative rates of olefin cleavage by photoexcited nitroarenes. The
single case of poor correlation, between relative rates and the Loewdin
charges on nitrogen sites, is ameliorated when considering the net
charge on the NO2 group. Third, we show that Loewdin, Hirshfeld,
and CM5 charges all perform very well for generating correlations
for relative reaction rates for C–H activation of 9-(4-X-phenyl)-9H-fluorene substrates by a transition metal catalyst. The
equations generated throughout the study enable the prediction of
Hammett parameters and relative reaction rates. These tools can accelerate
synthetic and experimental studies by enabling the in silico prediction
of uncharacterized chemical properties.