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Chemical reactivity properties such as regioselectivity, electrophilicity and nucleophilicity are important chemical concepts, yet their understanding and quantification are still far from being accomplished. Applying density functional theory (DFT) to appreciate these properties is one route to pursue in the literature. In this work, we present a comparative study to benchmark two approaches in DFT to predict regioselectivity, electrophilicity and nucleophilicity: one with the Hirshfeld charge and the other with the Fukui function. We also examine the impact of 15 different ways to compute atomic charges on the performance of their predictions about these chemical reactivity properties. Our results show that the Hirshfeld charge is able to reliably determine regioselectivity and simultaneously accurately quantify both electrophilicity and nucleophilicity. The Fukui function behaves reasonably well for the prediction of electrophilicity but performs poorly for nucleophilicity. Among all other atomic charges examined in this study, it is only the Voronoi deformation density charge that yields the similar result as the Hirshfeld charge. As the first systematic benchmark study in the literature to compare the two available approaches in DFT about reactivity predictions, this work should fill in the needed knowledge gap and provide an impetus for the future development of chemical reactivity theory using DFT language.

Chemistry of nitro groups and nitro compounds has long been intensively studied. Despite their long history, new reactions and methodologies are still being found today. This is due to the diverse reactivity of the nitro group. The importance of nitro chemistry will continue to increase in the future in terms of elaborate synthesis. In this article, we will take a walk through the recent advances in nitro chemistry that have been made in past decades.

We show the relation between the “|Δμ| big is good” rule and the maximum hardness and the minimum electrophilicity principles. We focus on a double-exchange acid–base (e.g., charge transfer) reaction. We then prove that the species favored by the “|Δμ| big is good” rule are those such that the multiplication of their hardnesses is the biggest, while the validity of the minimum electrophilicity principle requires other conditions.

A 12-membered pyridinophane scaffold containing two pyridine and two tertiary amine residues is examined as a prototype ligand (tBuN4) for supporting nitrene transfer to olefins. The known [(tBuN4)MII(MeCN)2]2+ (M = Mn, Fe, Co, and Ni) and [(tBuN4)CuI(MeCN)]+ cations are synthesized with the hexafluorophosphate counteranion. The aziridination of para-substituted styrenes with PhI=NTs (Ts = tosyl) in various solvents proved to be high yielding for the Cu(I) and Cu(II) reagents, in contrast to the modest efficacy of all other metals. For α-substituted styrenes, aziridination is accompanied by products of aziridine ring opening, especially in chlorinated solvents. Bulkier β-substituted styrenes reduce product yields, largely for the Cu(II) reagent. Aromatic olefins are more reactive than aliphatic congeners by a significant margin. Mechanistic studies (Hammett plots, KIE, and stereochemical scrambling) suggest that both copper reagents operate via sequential formation of two N–C bonds during the aziridination of styrene, but with differential mechanistic parameters, pointing towards two distinct catalytic manifolds. Computational studies indicate that the putative copper nitrenes derived from Cu(I) and Cu(II) are each associated with closely spaced dual spin states, featuring high spin densities on the nitrene N atom. The computed electrophilicity of the Cu(I)-derived nitrene reflects the faster operation of the Cu(I) manifold.

The electrophilic activation of various substrates via double or even triple protonation in superacidic media enables reactions with extremely weak nucleophiles. Despite the significant progress in this area, the utility of organophosphorus compounds as superelectrophiles still remains limited. Additionally, the most common superacids require a special care due to their high toxicity, exceptional corrosiveness and moisture sensitivity. Herein, we report the first successful application of the “Brønsted acid assisted Brønsted acid” concept for the superelectrophilic activation of 2-hydroxybenzo[e][1,2]oxaphosphinine 2-oxides (phosphacoumarins). The pivotal role is attributed to the tendency of the phosphoryl moiety to form hydrogen-bonded complexes, which enables the formation of dicationic species and increases the electrophilicity of the phosphacoumarin. This unmasks the reactivity of phosphacoumarins towards non-activated aromatics, while requiring only relatively non-benign trifluoroacetic acid as the reaction medium.

Predicting the reactivity of nucleophilic reaction at different sites has important theoretical and practical significance. Many prediction methods solely based on the electronic structure of reactants have been proposed. In this paper, detailed comparative analyses on the reliability of 14 methods are carried out and three series of molecules, carbonyl compounds, aromatic hydrocarbons and pyridine derivatives are exploited as test systems. It is found that the methods reflecting local electronic softness, such as condensed dual descriptor, have satisfactory prediction ability; while the ones reflecting electrostatic effect, such as atomic charge analysis and electrostatic potential analysis, have evidently worse overall performance. For all systems of interest, condensed dual descriptor and Hirshfeld charge display the most robust predictive capacity.

The electronic effects of Lewis acids (LAs) in reducing the activation energies of Alder-ene (AE) reactions have been studied within the Molecular Electron Density Theory (MEDT). To this end, the AE reactions of 2-methylbutadiene (2MBD) with formaldehyde (CHO) in the presence of three LAs with increasing acidic character, BH3, BF3, and AlCl3, have been studied. Topological analysis of the electron density and the evaluation of the DFT-based reactivity indices indicate that LAs do not modify the electronic structure of the carbonyl group but markedly increase the electrophilic character of CHO. LAs not only strongly accelerate the AE reactions, but also modify the molecular mechanisms, changing them from a non-concerted two-stage one-step mechanism to a two-step one. Topological analyses of the electron density at the transition state structures (TSs) indicate that while the formation of the new C-C single bond has begun, the departure of the hydrogen has not yet started. A Relative Interacting Atomic Energy (RIAE) analysis of the activation energies allows the establishment of the electronic effects of LAs on the AE reactions. LAs increase the global electron density transfer (GEDT) occurring in polar AE reactions; this phenomenon markedly stabilizes the CHO framework at the TSs, decreasing the RIAE relative energies.

The prediction of the nature of a reactivity descriptor is of paramount importance to theoretical chemists and thus, much work has been carried out in this area. The electrophilicity index (ω), an important theoretical construct of chemistry, is a measure of the electron acceptor affinity to gain an additional electronic charge from the environment. It is quantified in terms of the maximum energy stabilization in species, which arises due to accepting a charge. The electrophilicity concept is being extensively used in modern chemistry, although the finest measurement scale of the electrophilicity index is yet to be designed. In this study, a new scale of the electrophilicity index invoking the force concept based on the effective nuclear charge (Zeff) and absolute atomic radii (r) is proposed for 97 elements of the periodic table, which is determined through the regression analysis. The computed data follows the periodicity very well satisfying the sine qua non of the standard scale of the electrophilicity index. The electrophilicity equalization principle is also established in terms of the computed data. To test the model in the real field, the internuclear bond distance of some molecules is calculated in terms of the computed electrophilicity index. A comparative study of the theoretical vis-à-vis experimental internuclear bond distance reveals the efficacy of the proposed scale.

This research presents an innovative approach for synthesizing 2-amino-4 H -chromene derivatives, utilizing 30 mg of NS-doped graphene oxide quantum dots (GOQDs) as a catalyst in a one-pot, three-component reaction conducted in ethanol. The NS-doped GOQDs were synthesized using a cost-effective bottom-up method through the condensation of citric acid (CA) with thiourea and the reaction was carried out at 185 ∘ C, resulting in the elimination of water. The catalytic performance of the synthesized NS-doped GOQDs resulted in high product yields, achieving up to 98% for the 2-amino-4 H -chromene derivatives from aromatic aldehydes, malononitrile, resorcinol, β -naphthol, and dimedone. The reaction showcased rapid completion time (typically < 2 h), low-cost reagents, and easy work-up procedures. In addition, the study integrates experimental and theoretical analyses, including density functional theory (DFT) calculations, to investigate the electronic properties of the synthesized compounds. Calculated HOMO and LUMO energies indicate efficient charge transfer within the molecular structure. The FT-IR spectra of compound 4c were recorded in the range of 4000–500 cm - 1 , and vibrational frequencies were computed at the B3LYP/6-311+G(d,p) level, correlating well with experimental data. Detailed analyses, including Mep surfaces, Mulliken population analysis, and Natural Bond Orbital (NBO) analysis, provide further insights into the electronic distribution and reactivity of the compounds. Furthermore, comparative 1 H and 13 C NMR analyses of compound 4c reveal strong agreement between computational and experimental findings. This research not only validates the synthetic method but also emphasizes the dual experimental and computational approach in understanding the structural and electronic characteristics of the 4c compound.

Electrophilicity is an intrinsic property of atoms and molecules. It probably originates logistically with the involvement in the physical process of electrostatics of soaked charge in electronic shells and the screened nuclear charge of atoms. Motivated by the existing view of conceptual density functional theory that similar to electronegativity and hardness equalization, there should be a physical process of equalization of electrophilicity during the chemical process of formation of hetero nuclear molecules, we have developed a new theoretical scheme and formula for evaluating the electrophilicity of hetero nuclear molecules. A comparative study with available bench marking reveals that the hypothesis of electrophilicity and equalization, and the present method of evaluating equalized electrophilicity, are scientifically promising.