On the reliability of global and local electrophilicity descriptors

The global electrophilicity index w (as defined by Parr et al. J. Am. Chem. Soc. 1999, 121, 1992) and local ''philicity" index, w(k)(alpha) (as defined by Chattaraj et al. J. Phys. Chem. A 2003, 107, 4973) of some carbonyl compounds are evaluated on the basis of Mulliken population analysis (MPA) and Hirshfeld population analysis (HPA) schemes. It is observed that the local electrophilicity indices (i.e., w(k)(+)), extracted from both HPA and MPA based charge, produce reliable intermolecular electrophilicity trends except in one case each. However, the reliability is lost in some cases when w is used. It is also shown both through numerical demonstrations and analytical proof that for generating intramolecular reactivity trends "philicity" index does not provide any extra reliability over local softness or Fukui function values. "Relative electrophilicity" and "relative nucleophilicity", as defined by Roy et al. (J. Phys. Chem. A 1998, 102, 3746), generate the most reliable intramolecular reactivity (i.e., site selectivity) sequences.