Stockholders Charge Partitioning Technique. A Reliable Electron Population Analysis Scheme to Predict Intramolecular Reactivity Sequence

Abstract

Stockholders charge partitioning (i.e., Hirshfeld population analysis) is used to evaluate the intramolecular reactivity sequence (i.e., site selectivity) of some chosen alkyl halides. It is shown that the local reactivity descriptors, e.g., condensed local softness (or condensed Fukui function indices) in general and “relative electrophilicity” and “relative nucleophilicity” in particular, when evaluated by Hirshfeld population analysis, correctly reproduce the strongest electrophilic center in all 18 systems chosen in the present study. No manipulation of the charge summation scheme, i.e., addition of H-charges on the carbon atoms to which they are bonded, is required here as was done in a previous study (Roy, R. K. J. Phys. Chem. 2003, 107, 397) on the same systems using Mulliken population analysis. Extension of the study to polyfunctional systems (e.g., m-chloroaniline and m-anisidine) also shows that HPA correctly predicts the gas phase protonation site although MPA fails. This clearly indicates that Hirshfeld population analysis is superior to Mulliken population analysis as a charge-partitioning scheme (i.e., Hirshfeld population analysis provides a more reliable definition of atoms in molecules) as long as the intramolecular reactivity trend is concerned.