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1 2024

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Zastosowanie metod chemii kwantowej do interpretacji efektu podstawnikowego w wybranych układach cyklicznych zawierających grupę nitrową

Jezuita Anna, Szatyłowicz Halina, Krygowski Tadeusz Marek, Ejsmont Krzysztof

Wiadomości Chemiczne

2024

[Z] 78, 5-6

563--586

This study presents an investigation of substituent effect (SE) in physical term, using quantum chemistry modeling. Substituent effect in series of meta(1,3-) and para(1,4)-X-substituted nitro derivatives of cyclic systems: benzene (BEN), cyclohexa-1,3-diene (CHD) and para-bicyclo[2,2,2]octane (BCO), with 16 different substituents (X = NMe2, NH2, OH, OMe, CH3, H, F, Cl, CF3, CN, CHO, COMe, CONH2 , COOH, NO2, NO), was analyzed. To describe the SE, quantum chemistry models: cSAR (charge of the substituent active region), SESE (substituent effect stabilization energy) and π/beta Electron Donor/Acceptor indices (pEDA/sEDA) were used. Delocalization of πelectron in the transmitting moiety (BEN, butadiene fragment of the CHD) was described by index HOMA and pEDA parameter for transmitter [pEDA(R)]. The novelty of the analysis presented here is its description of SE by the population of electrons in sigma and pi orbitals for both the nitro group and the ring for derivatives of para- and meta-substituted nitrobenzene and para-type cyclohexadi-1,3-ene systems. Application of quantum chemical modeling made it possible to compare the substituent effects observed in systems differ the nature of transmitter. It was observed that strength of substituent effect decrease in a sequence: olefinic CHD, aromatic BEN and aliphatic BCO. The obtained results clearly document different nature of intramolecular interactions between NO2 group and X in BEN and CHD systems (coexistence of resonance and inductive effects) than in BCO ones (only the inductive effect). Additionally, it was shown that the difference in SESE values for aromatic (BEN) and aliphatic (BCO) series, ΔSESE, may be considered as a measure of the resonance effect of substituent X. An important aspect of this research is showing that descriptors of SE may also be applied to characterize the strength of impact of substituent in water (by PCM model - Polarizable Continuum Model). The obtained data measured by means of SESE and cSAR approaches exhibit a good agreement with traditionally Hammett constants and commonly accepted empirical concepts. The advantage of using these modeling is that they can be applied to any kind of molecules studies in the field of organic and bioorganic chemistry. The results contain the influence of substituent X on electronic properties of the NO2 group (classical substituent effect) and the impact of the NO2 group on electronic properties of substituent X (reverse substituent effect), inductive and resonance effects of nitro groups, changes in the π and beta electron structure of transmitter (R) and NO2 groups and solvent effect on the strength of these interactions.