No abstract

The topological analysis of the electron localization function ELF provides a partition of the molecular space into basins of attractors which have a clear chemical signification. The hierarchy of these basins is given by the bifurcation of the localization domains. In the case of π-donor substituents (OH, NH 2 , F, CH 3 , C 6 H 5 , Cl), the aromatic domain is first opened close to the substituted carbon and then in the vicinity of the meta carbon; whereas for attractor substituents (CN, CHO, NO 2 , CF 3 and CCl 3 ), it is first opened in the ortho and para positions. The orienting effects of the electrophilic substitutions are correlated with these bifurcations. The experimental favored positions always correspond to the locally electronegative carbons (i.e., those which keep their shell structure at the higher ELF values). This suggests that the local Pauli repulsion plays a noticeable role in the orienting effects which are complementary to the charge transfer effect involved in standard quantum chemical pictures.

B3LYP/aug-cc-pVTZ calculations were performed on the species with intramolecular O-H···O hydrogen bonds. The Quantum Theory of Atoms in Molecules (QTAIM) and the Electron Localization Function (ELF) method were applied to analyze these interactions. Numerous relationships between ELF and QTAIM parameters were found. It is interesting that the CVB index based on the ELF method as well as the total electron energy density at the bond critical point of the proton-acceptor distance (H(bcp)) may be treated as universal descriptors of the hydrogen bond strength, they are also useful to estimate the covalent character of this interaction. There are so-called resonance-assisted hydrogen bonds (RAHBs) among the species analyzed here. It was found that there are not any distinct differences between RAHBs and the other intramolecular hydrogen bonds.