σ‐ and π‐electron contributions to the substituent effect: natural population analysis

Abstract

Two independent s-and p-substituent effect descriptors, sEDA and pEDA, were constructed using the Natural Population Analysis (NPA) approach. The descriptors are based on parameters of 32 monosubstituted benzene molecules calculated at the B3LYP/6-31G ** level which is easily applicable to large molecular systems. The sEDA and pEDA descriptors have a clear physical meaning-they show to what extent the s and p electrons are donated or withdrawn by the substituent from the substituted system. The descriptors were successfully tested to be independent of either of the applicable theoretical methods (DFT or MP2), basis set (6-31G ** or cc-pVTZ), and solvent presence. We also demonstrated that the sEDA descriptor described equally well methane derivatives, whereas the pEDA descriptor explained behavior of ethene derivatives. Moreover, the two descriptors work out well for as different molecular systems as triazoles. A comparison of the sEDA and pEDA descriptors with the selected well-known substituent effect scales shows that the sEDA descriptor correlates well (R ¼ 0.961) with the Boyd & Boyd/Boyd-Edgecombe x descriptor and that so does also the pEDA descriptor (R ¼ 0.943) with the Taft-Topsom s R -resonance constant.

Sigma- and pi- electron structure of aza-azoles

“…If the molecule is oriented in the xy plane the s, p x and p y natural atomic orbitals (NAOs) occupations can be directly assigned to -electronic system and the p z NAOs occupations to -electronic system. We used similar approach in our previous study about substituted benzene molecules [17].…”

Substituent effects in 1-nitro-4-substituted bicyclo[2.2.2]octane derivatives: inductive or field effects?

“…The substituent effect was investigated by means of three methodologies, as follows:. Substituent effect stabilization energy (SESE) [40,41] for p-substituted nitrobenzene is defined as the zero-point corrected energy of the homodesmotic reaction (1) Sigma and pi electron donor acceptor (sEDA/pEDA) indices [35] were calculated for the NO 2 group according to Eqs. (2) and (3).…”

“…The question is how the meta-and para-type substituent interactions in benzene derivatives look out for 1,3 and 1,4-derivatives of 1-nitro-4-substituted bicyclo [2.2.2]octane. The nitro group as a sensor for both resonance and inductive/field interactions formed the subject of our investigations by means of homodesmotic reactions (SESE), by analyses based on natural bond orbital (NBO) methods [34,35], which allow estimation of changes in sigma and pi electron structures in the nitro group due to substituents from the 3-to 4-positions. For the same purpose, the concept of cSAR (charge of the substituent active region) [36][37][38], where the total charges of substituents and the fixed group (NO 2 ) are taken into account, was applied.…”

Aromatic character of heptafulvene and its complexes with halogen atoms

“…The π-electron count based aromaticity index pEDA [47] (π-electron donor acceptor) was calculated by summing the 2p z natural atomic orbital occupancies of the heptafulvene ring carbon atoms and subtracting 6, thus indicating how much the π population of the ring deviates from the ideal sextet:…”