Substituent effects of nitro group in cyclic compounds
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REVIEW ARTICLE
Substituent effects of nitro group in cyclic compounds Anna Jezuita 1,2 & Krzysztof Ejsmont 1
&
Halina Szatylowicz 3
Received: 6 July 2020 / Accepted: 9 August 2020 # The Author(s) 2020
Abstract Numerous studies on nitro group properties are associated with its high electron-withdrawing ability, by means of both resonance and inductive effect. The substituent effect of the nitro group may be well described using either traditional substituent constants or characteristics based on quantum chemistry, i.e., cSAR, SESE, and pEDA/sEDA models. Interestingly, the cSAR descriptor allows to describe the electron-attracting properties of the nitro group regardless of the position and the type of system. Analysis of classical and reverse substituent effects of the nitro group in various systems indicates strong pi-electron interactions with electron-donating substituents due to the resonance effect. This significantly affects the pi-electron delocalization of the aromatic ring decreasing the aromatic character, evidenced clearly by HOMA values. Use of the pEDA/sEDA model allows to measure the population of electrons transferred from the ring to the nitro group. Keywords Nitro group . Substituent effects . Molecular modeling . Sigma and pi electron structure . Substituent effect stabilization energy . Charge of the substituent active region
Introduction The nitro group is one of the most interesting and important substituents in organic chemistry and related fields [1–4]. Many monographic articles are available in the literature on the various properties and applications of nitro compounds. For example, according to ISI Web of Science [5], almost 2000 articles and 55 reviews containing the term “nitro” in the title have been published in the last 5 years. Moreover, in the Cambridge Structural Database (CSD) [6], about 51,500 crystal structures This review is dedicated to our friend and mentor Professor Tadeusz Marek Krygowski of the Department of Chemistry of the Warsaw University in gratitude for his guidance, support, and engagement in our research. * Anna Jezuita [email protected] * Halina Szatylowicz [email protected] 1
Faculty of Chemistry, Opole University, Oleska 48, 45-052 Opole, Poland
2
Faculty of Science and Technology, Jan Dlugosz University in Czestochowa, Al. Armii Krajowej 13/15, 42-200 Czestochowa, Poland
3
Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland
of chemical compounds containing the NO2 group are reported, of which almost 48,500 structures with an R-factor equal to or less than 0.10. It should be emphasized that nitro compounds are widely used in medicinal and pharmaceutical chemistry [7], explosives [8, 9], fertilizers [10], etc. The unusual interest in nitro compounds is associated with the strongly electron-attracting (EA) character of the nitro group. Its EA ability is a result of both strong inductive and resonance activities. Its inductive effect, estimated by σI at 0.76 [11], results from a high group electronegativity χ
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