An Efficient Computational Approach for the Evaluation of Substituent Constants

Abstract

Density functional theory computations at the B3LYP/6-311+G(2d,2p) and BPW91/6-311G(d,p) levels were carried out for a series of 15 monosubstituted benzene derivatives to study dependencies between electronic structure parameters and experimental reactivity constants. An efficient and accurate computational approach for the evaluation of sigma(0) substituent constants for substituted benzene systems is outlined. It is based on the excellent linear correlation between the experimental reactivity constants and the theoretical electrostatic potential values (EPN) at the carbon atoms in the para and meta positions. The results underline the usefulness of the EPN as a local reactivity descriptor. Theoretical computations to assess the influence of water solvent using the SCIPCM method showed that the solvent enhances the overall effect of polar substituents by about 30%. The results obtained indicate also that the relative values of the sigma(0) constants are predominantly determined by intramolecular influences.

Towards physical interpretation of Hammett constants: charge transferred between active regions of substituents and a functional group

“…-electron densities at p-and m-positions in monosubstituted benzenes [34] -electrostatic potential values at the ring carbon atoms [28,35,36] -electrostatic potential values at atoms of a reaction center [28,37] -topography of electrostatic potential near the molecular surface [38][39][40][41][42] -hyperpolarizability [43] -a complexed metal chemical shift [44,45] -energy of the highest occupied orbital (E HOMO ) [46,47] -energy of the lowest unoccupied orbital (E LUMO ) [16] -ionization potential [48] -electrophilicity, being a measure of stabilization in energy when the system acquires an additional electronic charge DN from the environment [28,49,50] -core electron binding energy shifts [51,52] -intramolecular charge transfer between oxygen or sulfur lone pair and an adjacent orbital, both within the reaction active center [53,54] -the so-called quantum chemical topology descriptors constructed using properties of the bond critical points, BCP, where BCP is the saddle points in the electron density [55][56][57][58] -charge of the reaction active site [42,47,59,60] -energy of p-conjugation [61] -charge of the substituent active space [58,[62][63][64].…”

Effects of structural variations on the hydrogen bond pairing between adenine derivatives and thymine

“…Since the atoms in the vicinity of N1 and N6 atoms in adenine remain the same throughout the investigated series (Scheme 1), it can be considered that the shifts of V Y (Y = N1, H6) upon the distant structural variations (at position C8) are dominated by electron density variations near atoms Y. Numerous successful application of EPN as a reactivity index for hydrogen bonding and chemical reactivity confirm the credibility of this hypothesis [53][54][55][56][57][58][59][60][61][62][63][64][65]. Figure 1 illustrates key geometrical parameters of some optimized complexes.…”

“…Z A is the charge of nucleus A at position R A , and ρ(r) is the electron density func-tion. Following the original findings [53][54][55][56][57] that EPN values define quantitatively the ability of molecules to form hydrogen bonds, the EPN index was extensively applied in describing both hydrogen bonding and chemical reactivity of various molecular systems [58][59][60][61][62][63][64][65]. In a recent review, we surveyed the application of EPN in quantifying various molecular properties of aromatic systems [62].…”

Theoretical vs. Experimental Ir Frequency Shifts Upon Π- Hydrogen Bonding: Complexes of Substituted Phenols With Hexamethylbenzene

“…EPN was first introduced by Wilson in 1962 [41]. In a number of studies from our laboratory, we have established that EPN is a remarkably accurate descriptor of the abilities of specific atomic centers in molecules to form hydrogen bonds [42][43][44][45][46][47] and also in quantifying chemical reactivity [48][49][50][51]. In later years, EPN values have been successfully employed by other authors in examining reactivity trends [52][53][54][55][56][57][58][59][60].…”