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Vibrational Strong Coupling (VSC) has been reported to change the rate of organic reactions. However, a lack of convenient and reliable methods to measure reaction kinetics under VSC makes it challenging to obtain mechanistic insight into its influence, hindering progress in the field. Here, we use recently developed fixed‐width optical cavities to obtain large kinetic datasets under VSC with small errors (±1–5 %) in an operationally simple manner using UV/Vis spectroscopy. The setup is used to test whether VSC changes a fundamental kinetic property of polar reactions, nucleophilicity, for water and alcohols, species commonly used in VSC‐modified chemistry. We determined the rate constants for nucleophilic capture with a library of benzhydrilium ions as reference electrophiles with and without strong coupling of the nucleophile's key vibrations. For all investigated combinations of electrophiles and nucleophiles, only minor changes in the observed rate constants of the reactions were observed independently of the coupled bands. These results indicate that VSC does not substantially alter the nucleophilicity of water and alcohols, suggesting that polar reactions are modified through other, presently unknown mechanisms. Fixed‐width cavities allow for convenient and reproducible UV/Vis kinetics, facilitating mechanistic studies of VSC‐modified chemistry. [ABSTRACT FROM AUTHOR]

The efficient acetate conversion from CO electroreduction is challenging due to the poor selectivity at high reaction rate, which requires the competition with H2 and other C2+ (i. e., ethylene, ethanol, n‐propanol) reduction products. Electrolyte engineering is one of the efficient strategies to regulate the reaction microenvironment. In this work, the adding of sulfite (SO32−) with high nucleophilicity in KOH electrolytes was demonstrated to enable improving the CO‐to‐acetate conversion via generating a S−O chemical bond between SO32− and oxygenated *C2 intermediates (i. e., *CO−CO, *CO−COH) compared with that in pure KOH system on both synthesized Cu(200)‐ and normal commercial Cu(111)‐facets‐exposed metallic Cu catalysts. As a result, the prepared Cu(200)‐facets‐exposed metallic Cu catalyst with surface ions modification showed an superior Faradaic efficiency of 63.6 % at −0.6 A ⋅ cm−2, and extraordinary absolute value of peak partial current density as high as 1.52 A ⋅ cm−2 with adding SO32− in KOH electrolytes, compared to the best reported values in both CO and CO2 electroreduction. Our work suggests an attractive strategy to introduce the oxyanion with high nucleophilicity in electrolytes to regulate the microenvironment for industrial‐current‐density electrosynthesis of acetate from CO electroreduction. [ABSTRACT FROM AUTHOR]

Radical philicity and polar effects are key concepts underpinning radical reactivity and selectivity. In general, the radical species can be divided into two classes, namely, electrophilic and nucleophilic, on the basis of its reactivity, atom electronegativity, and stability of the resulting species through electron gain or loss. In this article we aim to establish guidelines for understanding radical philicity from different carbon-centered and heteroatom-centered radicals and we accompany our discussion with representative synthetic examples. [ABSTRACT FROM AUTHOR]

Traditional lithium salts typically adhere to the designing principles of enhancing cation‐anion dissociation degree to obtain a high electrolyte conductivity. This promotes the invention of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), where the symmetric electron‐withdrawing trifluoromethanesulfonyl groups significantly delocalize the negative charge density around the nitrogen atom, thereby weakening the electrostatic interaction between Li+ and the anion. Herein, deviating from the general principle, lithium (methanesulfonyl)(trifluoromethanesulfonyl) imide (LiMTFSI) is deliberately designed by substituting a unilateral electron‐withdrawing trifluoromethyl (─CF3) group of LiTFSI with an electron‐donating methyl (─CH3) group, to tune the nucleophilicity of the anion. This modification enhances Li‐anion interaction, causing the anion to replace the solvent molecules in the Li+ solvation shell. Additionally, the MTFSI− anion exhibits an elevated donor number to facilitate the solubility of LiNO3 in carbonate‐based electrolytes. The synergistic effect of these changes suppresses the decomposition of solvent and helps construct a stable solid electrolyte interphase (SEI) enriched with multiple inorganic lithium salts (e.g., Li2S, Li3N, and LiNxOy) on the Li metal anode, which enables the 500 mAh Li||LiNi0.5Co0.2Mn0.3O2 pouch cell to operate steadily for 150 cycles. It is believed this work would provide new insights and another dimension for designing functional anions beyond their role as charge carriers. [ABSTRACT FROM AUTHOR]

The high reactivity of 2‐methylene‐1,2‐dihydropyridines also known as 2‐methylpyridinium derived N‐heterocyclic olefins (2‐pyNHOs) has been recognized in organic synthesis, yet a quantification of their nucleophilicity is lacking. Herein we used stopped‐flow photometry to determine the nucleophilicity of a series of 2‐pyNHOs from the kinetics of their reactions with quinone methides and benzhydrylium ions as reference electrophiles in four organic solvents at 20 °C. The kinetic data was evaluated by using the Mayr‐Patz equation, lg k(20 °C)=sN(N+E), which gave nucleophilicity parameters N (and sN). With N in the range of 19.4–21.2 (in DMSO), 2‐pyNHOs exceed the reactivity of classical enamines, such as pyrrolidino‐cyclopent‐1‐ene. The addition of 2‐pyNHOs to quinone methides resulted in the formation of zwitterionic adducts with pyridinium and phenolate moieties. Subsequent tautomerization yielded entirely neutral pyridine‐2(1H)‐ylidene‐phenol species in several cases. Formation of the zwitterionic adducts from 2‐pyNHOs and neutral electrophiles was almost equally fast in the polar solvents acetonitrile and DMSO, but proceeded one to two orders of magnitude slower in the less polar solvents dichloromethane or THF. [ABSTRACT FROM AUTHOR]

Context: Electrophilicity and nucleophilicity are two vastly important chemical concepts gauging the capability of atoms in molecules to accept and donate the maximal number of electrons. In our earlier studies, we proposed to simultaneously quantify them using the Kullback–Leibler divergence from the information-theoretic approach in density functional theory. However, several issues with this scheme remain to be clarified such as its general validity, predictability, and relationship with other information-theoretic quantities. In this work, we revisit the matter with bigger datasets and deeper theoretical insights. Five information-theoretic quantities including Kullback–Leibler divergence, Hirshfeld charge, Ghost-Berkowitz-Parr entropy, and second and third orders of relative Onicescu information energy are found to be reliable and robust descriptors of electrophilicity and nucleophilicity propensities. Employing these five descriptors, we design a list of new compounds and predict their electrophilicity and nucleophilicity scales. This work should markedly improve our confidence and capability in applying information-theoretic quantities to evaluate electrophilicity and nucleophilicity propensities and henceforth pave the route for more applications of these quantities from information-theoretic approach in density functional theory in the future. Methods: All structures were fully optimized at the M06-2X/6–311 + G(d) level of DFT functional using the Gaussian 16 package (version C01) with integration grids and tight self-consistent-field convergence. The solvent effect was taken into account by using the implicit solvent model (CPCM) in the CH2Cl2 solvent, and all 3D contour surfaces of Fukui function, local temperature, and ITA (information-theoretic approach) quantities were generated by GaussView. The Multiwfn 3.8 program was used to calculate the ITA indexes and atomic charges. [ABSTRACT FROM AUTHOR]

Coumalic acid methyl ester (methyl coumalate), a biomass‐derived building block, was converted into (E)‐enaminoesters by an original uncatalyzed stereoselective 1,6‐addition/fragmentation cascade involving secondary amines. The transformation occurred under useful experimental conditions as a simple heating of a stoichiometric mixture of the starting compounds led to the desired products. The reaction could be extended to a range of alkyl coumalates and a variety of secondary amines. Given the original character of the transformation, the reaction mechanism was discussed. Therefore, the cascade is supposed to involve a 1,6‐conjugate addition followed by a fragmentation sequence leading ultimately to the decarboxylative elimination of (E)‐enaminoesters. Using this procedure, renewable coumalic acid proved to be a valuable alternative to fossil fuel‐based propiolates for the preparation of enaminoesters. [ABSTRACT FROM AUTHOR]

Context: Understanding and predicting the nucleophilic reactivity are paramount in elucidating organic chemical reactions and designing new synthetic pathways. In this study, we propose a nucleophilicity index within the framework of Conceptual Density Functional Theory (CDFT). Through rigorous theoretical formulations, we introduce an original quantum reactivity descriptor that captures the nucleophilic propensity of molecules based on their electronic structure and chemical environment. Subsequently, this proposed index is applied to a series of nucleophiles (pyrrolidines derivatives), spanning a diverse range of chemical functionalities. Our computational assessments reveal insightful correlations between the predicted nucleophilicity index and experimental observations of nucleophilic behavior. Thereby, they offer a promising avenue for advancing the understanding of organic reactivity and guiding synthetic efforts. Methods: Experimentally, Mayr's experimental parameters accounting for nucleophilicity were selected for the pyrrolidines. This study used DFT calculations at the B3LYP/Aug-cc-pVTZ level of theory using the Gaussian 16 program. Geometry optimization was thus performed, and the methodology employed for the computation of quantum reactivity descriptor is presented. Solvent effect was also taken into account using IEFPCM, and empirical dispersion correction (GD3) was employed. [ABSTRACT FROM AUTHOR]

Aluminum‐air battery (AAB) with alkaline‐based aqueous electrolyte have attracted intensive research interests due to high‐capacity density, low cost, and high safety. However, severe hydrogen evolution reaction (HER) of Al anode in alkaline electrolyte extremely restricts its large‐scale application. In this work, ZnO with a group of quaternary ammonium salts (QAS, denoted as C1, C2, C4, C6, and C8 depending on the length of non‐polar group) are introduced into electrolytes to inhibit HER. It is revealing that capacity density initially increases with C1, C2, or C4, up to 2564 mAh gAl−1 with anodic utilization rate of 86.0%, and then follows by a decline (C6 and C8). The addition of QAS creates "physical‐hydrophobic interface" by non‐polar group owing to its electrophilic property and constructs "chemical‐hydrophobic interface" with polar group by reducing water activity. QAS also promotes the uniform growth of Zn‐based film, as a barrier against H2O. Thus, HER is effectively inhibited to improve the capacity density. With further increasing non‐polar group length (C6 or C8), the bonding status of the film deteriorates with enhanced H2O activity, leading to the recurrence of HER. This work explores the effect of non‐polar groups on inhibiting HER and opens the door to stable anodes for alkaline‐based batteries. [ABSTRACT FROM AUTHOR]

We present a kinetic and theoretical study of electrophilic aromatic substitution (SEAr) involving 2-(2′,4′,6′-trinitrophenyl)-4,6-dinitrobenzotriazole 1-oxide 1 with a series of 5-R-substituted indoles 2a-e (R = CN, Cl, H, Me and NH2) in acetonitrile at 20 °C. Single electron transfer (SET) mechanism was proposed and confirmed by the agreement between the rate constants (k) and the oxidation potentials (Epox) of these series of indoles. Using Mayr's equation, the electrophilicity parameter (E) of 1 at C-7 position is derived and compared with the same parameter estimated using empirical equation E versus. pKa. Density Functional Theory (DFT) calculations were performed to confirm the suggested reaction mechanisms and elucidate the origin of the electrophilic reactivity of 1. Notably, a linear correlation (R2 = 0.9957) between the experimental nucleophilicity (N) and the theoretical model of nucleophilicity (ω−1) determined in this work of various 5-R-substituted indoles has been obtained and discussed. Mayr and Parr's approaches were combined with the correlation N vs ω−1 established in the present work, to evaluate the empirical electrophilicity parameter (E) of 2-(2′,4′,6′-trinitrophenyl)-4,6-dinitrobenzotriazole 1-oxide and the unknown nucleophile specific parameters (N and sN) of four new 5-R-substituted indoles (R = NO2, F, H and N(CH3)2) in acetonitrile. [ABSTRACT FROM AUTHOR]

Precise and timely recognition of hazardous chemical substances is of great significance for safeguarding human health, ecological environment, public security, etc., especially crucial for adopting appropriate disposition measures. Up to now, there remains a practical challenge to sensitively detect and differentiate organic amines with similar chemical structures with intuitive analysis outcomes. Here, a unique optical probe with two electrophilic recognition sites for rapid and ultra‐sensitive ratiometric fluorescence detection of ethylenediamine (EDA) is presented, while producing distinct fluorescence signals to its structural analog. The probe exhibits ppb/nmol level sensitivity to liquidous and gaseous EDA, specific recognition toward EDA without disturbance to up to 28 potential interferents, as well as rapid fluorescence response within 0.2 s. By further combining the portable sensing chip with the convolutional algorithm endowed with image processing, this work cracked the problem of precisely discriminating the target and non‐targets at extremely low concentrations. [ABSTRACT FROM AUTHOR]

Nucleophilic substitution reactions are elementary reactions in organic chemistry that are used in many synthetic routes. By quantum chemical methods, we have investigated the intrinsic competition between the backside SN2 (SN2‐b) and frontside SN2 (SN2‐f) pathways using a set of simple alkyl triflates as the electrophile in combination with a systematic series of phenols and partially fluorinated ethanol nucleophiles. It is revealed how and why the well‐established mechanistic preference for the SN2‐b pathway slowly erodes and can even be overruled by the unusual SN2‐f substitution mechanism going from strong to weak alcohol nucleophiles. Activation strain analyses disclose that the SN2‐b pathway is favored for strong alcohol nucleophiles because of the well‐known intrinsically more efficient approach to the electrophile resulting in a more stabilizing nucleophile–electrophile interaction. In contrast, the preference of weaker alcohol nucleophiles shifts to the SN2‐f pathway, benefiting from a stabilizing hydrogen bond interaction between the incoming alcohol and the leaving group. This hydrogen bond interaction is strengthened by the increased acidity of the weaker alcohol nucleophiles, thereby steering the mechanistic preference toward the frontside SN2 pathway. [ABSTRACT FROM AUTHOR]

Mesoionic polarization allows access to electron‐rich olefins that have found application as organocatalysts, ligands, or nucleophiles. Herein, we report the synthesis and characterization of a series of 3‐methylpyridinium‐derived mesoionic olefins (py‐mNHOs). We used a DFT‐supported design concept, which showed that the introduction of aryl groups in the 1‐, 2‐, 4‐, and 6‐positions of the heterocyclic core allowed the kinetic stabilization of the novel mesoionic compounds. Tolman electronic parameters indicate that py‐mNHOs are remarkably strong σ‐donor ligands toward transition metals and main group Lewis acids. Additionally, they are among the strongest nucleophiles on the Mayr reactivity scale. In reactions of py‐mNHOs with electron‐poor π‐systems, a gradual transition from the formation of zwitterionic adducts via stepwise to concerted 1,3‐dipolar cycloadditions was observed experimentally and analyzed by quantum‐chemical calculations. [ABSTRACT FROM AUTHOR]

Polyhedral boranes are a class of well-known boron molecular clusters with unique physical and chemical properties, and great efforts have been made in the past decades to find more effective synthetic methods. However, the established synthetic methods suffer from low efficiency and low selectivity because the mechanism of the B–H bond condensation reaction, critical for the synthesis of the polyhedral boranes, is not well understood. Here we report highly selective and efficient synthetic methods of the salts of the tetradecahydridoundecaborate (1–) (B11H14−) and dodecahydrido-dodecaborates (2–) (B12H122−) anions by employing commercially available and inexpensive starting materials. Both theoretical and experimental investigations are carried out to elucidate the reaction mechanisms. We have found that the nature of the B–H bond condensation is the dihydrogen bonding interaction in which the positively charged hydrogens (bridged hydrogens) play a crucial role. The current study has not only led to more effective and selective synthetic methods for B11H14− and B12H122− but also unveiled the nature of the B–H bond condensation and the general formation mechanisms of polyhedral boranes. This finding will facilitate the development of more effective synthetic methods for polyhedral boranes and spur their wide application. [ABSTRACT FROM AUTHOR]

Derived from malachite green, new triaryl-carbonium-ion-functionalized gold nanoparticles have been synthesized for detecting anions. The detection process, and concomitant colour change, is based on charge compensation on the surface of nanoparticles, which triggers their aggregation, resulting in a bathochromic shift of the plasmon resonance band. The difference in electrophilicity of the malachite green triaryl ions in solution or on gold nanoparticles makes it possible to distinguish different anions related to their nucleophilic character.

Derived from malachite green, new triaryl-carbonium-ion-functionalized gold nanoparticles have been synthesized for detecting anions. The detection process, and concomitant colour change, is based on charge compensation on the surface of nanoparticles, which triggers their aggregation, resulting in a bathochromic shift of the plasmon resonance band. The difference in electrophilicity of the malachite green triaryl ions in solution or on gold nanoparticles makes it possible to distinguish different anions related to their nucleophilic character. [ABSTRACT FROM AUTHOR]

We have quantum chemically studied the influence of ring strain on the competition between the two mechanistically different SN2 and E2 pathways using a series of archetypal ethers as substrate in combination with a diverse set of Lewis bases (F−, Cl−, Br−, HO−, H3CO−, HS−, H3CS−), using relativistic density functional theory at ZORA‐OLYP/QZ4P. The ring strain in the substrate is systematically increased on going from a model acyclic ether to a 6‐ to 5‐ to 4‐ to 3‐membered ether ring. We have found that the activation energy of the SN2 pathway sharply decreases when the ring strain of the system is increased, thus on going from large to small cyclic ethers, the SN2 reactivity increases. In contrast, the activation energy of the E2 pathway generally rises along this same series, that is, from large to small cyclic ethers. The opposing reactivity trends induce a mechanistic switch in the preferred reaction pathway for strong Lewis bases from E2, for large cyclic substrates, to SN2, for small cyclic substrates. Weak Lewis bases are unable to overcome the higher intrinsic distortivity of the E2 pathway and, therefore, always favor the less distortive SN2 reaction. [ABSTRACT FROM AUTHOR]

Using density-based quantities to establish a qualitative or even quantitative framework to predict molecular reactivity in density functional theory is of considerable interest in the current literature. Recent developments in information-theoretic approach (ITA) represent such a trend. Traditionally, we represent ITA quantities in terms of the electron density, shape function, and atoms in molecules. In this contribution, we expand the theoretical framework of ITA by introducing a new representation. To that end, we make use of the first-order partial derivative of ITA quantities with respect to the number of total electrons and then approximate them in the finite difference approximation. The new representation has both local (three-dimensional) and global (condensed to atoms) versions. Its close relationship with Fukui function from conceptual density functional theory was derived analytically and confirmed numerically. Extensions of our present approach to include other types of derivatives are discussed. This work not only enriches the theoretical framework of ITA with a new representation but also provides opportunities to expand its territory as well as the scope of its applicability in dealing with molecular processes and chemical reactivity from a new perspective. [ABSTRACT FROM AUTHOR]

The polarizable continuum model was used for four different compounds to investigate the impact of substituent groups, of the number of π-electrons, of the electron-accepting and electron-donating properties on the corrosion inhibiting properties in both aqueous and gas phases for the neutral and cationic forms of the studied subsdtances. Measures for the corrosion prevention of metals are of great importance in the industrial, environmental (or ecologic), aesthetic, and economic fields. The use of inhibitors is the best way to preserve metals and alloys from corrosion. The purpose of this study was to apply quantum chemical calculations in the research of the corrosion inhibition and adsorption properties of four compounds with various heteroatoms or substituent groups but with similar chemical skeleton structures: 2-mercaptoimidazole, 2-mercapto-5-methyl benzimidazole, 2-mercaptobenzoimidazole, and 2-mercapto-5-nitrobenzimidazole, shown in Figs. 1 and 2 and designated as A, C, B, and D, respectively. The quantum chemical computations sector of the study gives complete calculation details and discussion on the correlation between corrosion inhibition and global reactivity descriptors such as the energy of the highest occupied molecule orbital, the energy of the lowest unoccupied molecule orbital, total energy, ionization energy, electron affinity, electronegativity, energy gap, hardness, softness, dipole moment, electron transfer, chemical potential, electrophilicity, nucleophilicity, and back-donation energy. The calculations were carried out using the general purpose computational chemistry software package Gaussian 09. The total calculations have been done based on the density functional theory at 6-311++G(d, p) basis set and applying the hybrid functional B3LYP level taking into account the exchange and the correlation with three parameters defining the hybrid Becke's functional (Becke—the exchange part, and Lee, Yang and Parr—the correlation part). Based on the calculations performed in this paper, the following summary ranking was obtained for the corrosion inhibition efficiency: A > B > C ≈ D for neutral forms and A > B > C > D for cationic forms in the gas phase, A > C ≈ D > B for neutral forms and A ≈ B > C > D for cationic forms in the aqueous phase. Thus, inhibitor A should be considered to be the best one in all cases. [ABSTRACT FROM AUTHOR]

The reference electrophilicity and nucleophilicity scales established at the B3LYP/6‐31G(d) level are herein extended by least squares regressions to the most common DFT computational methods used in theoretical organic chemistry studies, including B3LYP, MPWB1K, M062‐X, and ωB97x‐D, in combination with basis sets of the type 6‐31G and 6‐311G with different degrees of polarization and diffuse functions. Excellent linear correlations with coefficient of determination R2 values between 0.97 and 1.00 are obtained. In this work, the new lower and upper threshold values of the scales are established at 48 DFT computational levels, which enables the direct classification and quantification of the electrophilic and nucleophilic character of molecules without necessarily relying upon the B3LYP/6‐31G(d) scales. The present study shows that although the strong, moderate, or marginal thresholds of the electrophilicity and nucleophilicity scales can be modified up to a 24% (ωB97x‐D/6‐31G(d)) with the computational level, the relative position of the reagents on these scales does not change, allowing them to be used in the study of relative chemical reactivity. [ABSTRACT FROM AUTHOR]

High-level ab initio and density functional theory were applied to investigate property and reactivity of polyselenides and polysulfides. With CH3XnH (X = S or Se) we found that the deprotonation energy (and pKa) of CH3SenH, ionization potential (IP) of , and CH3Sen−H bond dissociation energy (BDE) are lower than those of their sulfur counterparts. For n = 2, IPs and X−H BDEs are exceptionally small. The relative nucleophilicity of C H 3 X n − vary with substrates. However, CH3SenH are more nucleophilic than CH3SnH due to their due to their lower deprotonation energy. The nucleophilicity of selenolates versus thiolates are related to the chemical nature. Selenium is more electrophilic than sulfur. [ABSTRACT FROM AUTHOR]

Following our previous surveys on group 14 divalents, we report new series of N‐heterocyclic germylenes (NHGe) and their analogs that are regarded as cyclic (1C–10C) and linear (1L–10L) forms. Their thermodynamic and structural parameters are compared and contrasted, at the B3LYP/6‐311++G** level of theory. The complexation of these NHGe with Cu metal is investigated. Various analyses such as the atoms in molecules (AIM), natural bond orbital (NBO), non‐covalent interaction (NCI), and ultraviolet‐visible (UV‐Vis) are performed to determine the strength of our germylenes to act as ligands. The results indicate that there are strong interactions between the metal‐ligand bonds with a high contribution of π‐back donation. Every linear germylene demonstrates a higher ability of σ‐donation and π‐acceptation. Our scrutinized germylenes turn out as remarkable ligands to the Cu that can be applied in several types of catalysis. [ABSTRACT FROM AUTHOR]

Succinic semialdehyde dehydrogenase (SSADH) catalyses the conversion of succinic semialdehyde into succinic acid and two electrons are transferred to NAD(P)+ to yield NAD(P)H. Our previous work has already reported the catalytic role of Cys289 of two‐cysteine SSADH from Acinetobacter baumannii (AbSSADH). However, the mechanistic role of the neighbouring conserved Cys291 and Glu255 remains unexplored. In this study, the functional roles of Cys291 and Glu255 in AbSSADH catalysis have been characterized. Results demonstrated that the E255A activity was almost completely lost, ~ 7000‐fold lower than the wild‐type (WT), indicating that Glu255 is very crucial and directly involved in AbSSADH catalysis. However, the C291A and C291S variants activity and catalytic turnover (kcat) decreased ~ 2‐fold and 9‐fold respectively. To further characterize the functional roles of Cys291, we employed two pH‐dependent methods; pre‐steady‐state burst amplitude and NADP–enzyme adduct formation. The results showed that the pKa values of catalytic Cys289 measured for the WT and C291A reactions were 7.8 and 8.7–8.8, respectively, suggesting that Cys291 can lower the pKa of Cys289 and consequently trigger the deprotonation of a Cys289 thiol. In addition, the Cys291 also plays a role in disulfide/sulfhydryl redox regulation for AbSSADH activity. Hence, we demonstrated for the first time the dual functions of Cys291 in enhancing the nucleophilicity of the catalytic Cys289 and regulating a disulfide/sulfhydryl redox switch for AbSSADH catalysis. The mechanistic insights into the nucleophilicity enhancement of the catalytic cysteine of AbSSADH might be applicable to understanding how the microenvironment increases cysteine reactivity in other enzymes in the aldehyde dehydrogenase superfamily. [ABSTRACT FROM AUTHOR]

A series of N6-substituted adenine–ferrocene conjugates was prepared and the reaction mechanism underlying the synthesis was explored. The SN2-like reaction between ferrocenoyl chloride and adenine anions is a regioselective process in which the product ratio (N7/N9-ferrocenoyl isomers) is governed by the steric property of the substituent at the N6-position. Steric effects were evaluated by using Charton (empirical) and Sterimol (computational) parameters. The bulky substituents may shield the proximal N7 region of space, which prevents the approach of an electrophile towards the N7 atom. As a consequence, the formation of N7-isomer is a kinetically less feasible process, i.e., the corresponding transition state structure increases in relative energy (compared to the formation of the N9-isomer). In cases where the steric hindrance is negligible, the electronic effect of the N6-substituent is prevailing. That was supported by calculations of Fukui functions and molecular orbital coefficients. Both descriptors indicated that the N7 atom was more nucleophilic than its N9-counterpart in all adenine anion derivatives. We demonstrated that selected substituents may shift the acylation of purines from a regioselective to a regiospecific mode.

The effect of solvents on the nucleophilicity of nucleophiles is an important teaching topic in organic chemistry. Considering the bimolecular nucleophilic substitution (SN2) reaction between methoxide (CH3O-) and thiomethoxide (CH3S-) anions with chloroform (CH3Cl) as a representative example, this paper designs a teaching case for integrating computational chemistry into the organic chemistry curriculum. By performing quantum chemical calculations, we determined the reaction mechanism, obtained the thermodynamic and kinetic information of the reactions, and investigated the effect of solvents on the properties of nucleophiles. Polar protic solvents, such as methanol and water, and polar aprotic solvents, such as acetone, acetonitrile, and chloroform, were analyzed. The nucleophilic index was also calculated to evaluate the nucleophilic reactivities of CH3O- and CH3S-. [ABSTRACT FROM AUTHOR]

Reduced nucleophilicities ИB of axially symmetric molecules B were determined from , where De is the equilibrium dissociation energy of the complexes B⋅⋅⋅XY, NB is the nucleophilicity of B, EXY is the electrophilicity of the halogen‐bond donor XY and σmin ${{\sigma }_{{\rm { min}}}{\rm \ }}$ is the minimum electrostatic surface potential of B. The series B⋅⋅⋅ClY, B⋅⋅⋅BrY, B⋅⋅⋅IY (Y=F, Cl, Br, I, CN, and CCH) as well as (B⋅⋅⋅XY, XY=F2, Cl2, Br2,and BrCl) of complexes were investigated. Molecules B were grouped so that the terminal atom involved in the halogen bond was fixed within the group. Groups having N as the terminal atom were RCN (R=CH3, H, and F) or RN (R=N and P), those with C as the terminal atom were RNC (R=H and F) and RC (R=O, S and Se), and those with a terminal O atom were R=C=O (R=O or S). Graphs of De ${{D}_{{\rm { e}}}}$ versus EXY for each group were straight lines through the origin, with generally different gradients, hence implying different NB. By contrast, when De/σmin ${{D}_{{\rm { e}}}/{\sigma }_{{\rm { min}}}}$ was the ordinate the lines conflated to give a single straight line, which then defines a common (reduced) nucleophilicity ИB for that group of B. Hence it was concluded that ИB is an intrinsic property of the terminal atom, independent of the remainder of B, and only weakly dependent on the type (C, N or O) of the terminal atom. Moreover, ИB for each B was the same as determined previously from the hydrogen‐bonded series B⋅⋅⋅HX, (X=F, Cl, Br, I, CN, CCH, and CP). [ABSTRACT FROM AUTHOR]

Diazocyclopentadiene reacts with benzhydrylium ions (Ar2 CH+) to give 2,5-dibenzhydryl-substituted diazocyclopentadienes. The kinetics have been determined photometrically in dichloromethane under pseudo-first-order conditions using diazocyclopentadiene in excess. Plots of the second-order rate constants (log k 2) versus the electrophilicity parameters E of the benzhydrylium ions gave the nucleo-philicity parameter N = 4.84 and susceptibility s N = 1.06 for diazo-cyclopentadiene according to the correlation log k (20 °C) = s N (E + N). Diazocyclopentadiene thus has a similar nucleophilic reactivity as pyrrole. Previously reported electrophilic substitutions of diazocyclopentadiene are rationalized by these parameters and new reaction possibilities are predicted. [ABSTRACT FROM AUTHOR]

• Dimer mechanism has been suggested to describe the reactions of three diethyl 4-X-substituted benzylidenemalonates (X = N (CH 3) 2 , OCH 3 and CH 3) with three cyclic secondary amines (morpholine, piperidine and pyrrolidine) in acetonitrile at 20 °C. • Three equilibrium constant K values of these amine dimers have been predicted according to the log k 1 K vs. s N (E + N) correlation (Eq. I) demonstrated in this work. log k 1 K (20 °C) = s N (E + N) + log K (I). • The expansion of the applicability of Mayr's equation (II) to these types of processes further demonstrates the generality of this relationship. log k (20 °C) = s N (E + N) (II). We report on a kinetic study for the nucleophilic addition reactions of diethyl 4-X-substituted benzylidenemalonates 1a-c (X = N (CH 3) 2 , OCH 3 and CH 3) with N-nucleophiles, such as morpholine 2a , piperidine 2b and pyrrolidine 2c by UV–vis spectroscopy in acetonitrile solution at 20 °C. The Hammett plots demonstrate much better linear correlations with σ p + constants than with σ p constants. These results are best interpreted in terms of ground state stabilization through resonance interactions between the electron-donating substituent and the CO 2 Et group. The effect of amine basicity on the reaction rate was examined quantitatively, leading to linear correlations with high β nuc values in the 0.82–0.93 range. The origin of the abnormally high β nuc values was interpreted in terms of dimer mechanism. Finally, with the help of our new proposed linear free energy relationship log k 1 K (20 °C) = s N (E + N) + log K, the stability of the dimer amines (K) have been evaluated from the measured apparent second-order rate constant (k 1 K) and the previously reported E, N and s N parameters of the employed electrophiles 1a-c and nucleophiles 2a-c. Additionally, a complementary theoretical study utilizing Density Functional Theory (DFT) with the B3LYP/6-311g(d,p) method was conducted in acetonitrile. An attempt is made to establish the correlation between equilibrium constant and stabilization energy the studied systems. Apparent second-order rate constants (k 1 K) for three cyclic secondary amines (morpholine, piperidine and pyrrolidine) addition to three diethyl 4-X-substituted benzylidenemalonates (X = N (CH 3) 2 , OCH 3 and CH 3) in acetonitrile at 20 °C were determined. Dimer mechanism was proposed. The new correlation analysis (log k 1 K vs. s N (N + E)) leads to the equilibrium constant K values of the three amine dimers. [Display omitted] [ABSTRACT FROM AUTHOR]

Reactivity of primary phosphines with two stoichiometric equivalents of imine results in the formation of bis‐α‐aminophosphines (2 a–e), which can be subsequently oxidized in the presence of S8 or H2O2 to generate air stable bis‐α‐aminophosphine sulfides (2 b–m(S/O)). To elucidate the mechanism of this three‐component reaction, Hammett analysis, kinetic isotope effect (KIE), and trapping experiments were performed. Ultimately a P(V)–P(III) tautomerization is invoked, followed by nucleophilic attack by the P(III) species to generate the desired products. [ABSTRACT FROM AUTHOR]

To reach new triplet ground state (T) silylenes, we compare and contrast acyclic silylenes with group 14 substituents (:Si(XH3)2 (X = C, Si, Ge, Sn, and Pb; 1C, 2Si, 3Ge, 4Sn, and 5Pb, respectively), at the B3LYP/6-311++G** level of theory. The results show that in going from 1C to 5Pb, the singlet-triplet energy gap (ΔES-T) and HOMO-LUMO energy gap (ΔEH-L) decrease while the nucleophilicity (N) increases. Structure 5Pb demonstrates the equal possibility of singlet and triplet ground states. Replacing one and two hydrogens with alkaline and alkaline earth metals leads to generate a new series of T silylenes with high stabilities. [ABSTRACT FROM AUTHOR]

In this theoretical research, we have investigated the substituent effect of singlet (s) and triplet (t) rNHGes with the fused various aromatic rings, at (U)B3LYP/AUG‐cc‐pVTZ and (U)M06‐2X/AUG‐cc‐pVTZ. All singlet and triplet rNHGes appear as minima and every singlet germylene displays more thermodynamic stability and more kinetic stability than its corresponding triplet state. Regarding to the relationship among germylenic center (—:GeC— moiety) and the substituted NH, PH, O, and S—heteroatoms, the order of thermodynamic stability based on singlet (s)–triplet (t) energy difference (ΔΕs‐t) and kinetic stability based on band gap (ΔΕHOMO‐LUMO) for the fused rings is ortho‐pyrrole > furan > thiophene > benzene > phosphole in a "zigzag" arrangement. Except for phosphole, every ortho‐heterocycle ring in a "zigzag" arrangement stabilizes rNHGe more than para‐heterocycle ring in a "chair" arrangement. Every triplet rNHGe shows lower frequency, lower polarity, higher nucleophilicity, lower electrophilicity and lower chemical hardness than the corresponding singlet rNHGe. The resonance effect and aromaticity character of the scrutinized rNHGes appears considerably dependent on the electronegativity, size, and topology of the substituted heteroatoms in the fused rings. [ABSTRACT FROM AUTHOR]

Highly regioselective synthesis of 12 new dispiroheterocycles containing aurone scaffold was reported via a three-component 1,3-dipolar cycloaddition reaction of azomethine ylide and (Z)-2-benzylidene-6-methoxybenzofuran-3(2H)-one derivatives in excellent yields (60–94%). The structures of all the desired products were fully confirmed by 1H NMR, 13C NMR, and FT-IR spectral data and CHN elemental analysis. In the second part of the paper, the 1,3-dipolar cycloaddition reaction between N-(1,3-dioxo-1,3-dihydro-2H-inden-2-ylidene)-N-methylmethanideaminium II as a 1,3-dipole and 2-benzylidene-6-methoxybenzofuran-3(2H)-one III as a dipolarophile was studied theoretically using density functional theory (DFT) at the B3LYP/6–31 + + G(d, p) computational level to shed light on the regioselective and mechanistic aspects. Two possible routes for the reaction were considered, and the regioselectivity was also studied. The DFT results showed that the high regioselectivity is in complete agreement with the experimental results. [ABSTRACT FROM AUTHOR]

H2S is well-known as a colorless, acidic gas, with a notoriously rotten-egg smell. It was recently revealed that H2S is also an endogenous signaling molecule that has important biological functions, however, most of its physiology and pathology remains elusive. Therefore, the enthusiasm for H2S research remains. Fluorescence imaging technology is an important tool for H2S biology research. The development of fluorescence imaging technology has realized the study of H2S in subcellular organelles, facilitated by the development of fluorescent probes. The probes reviewed in this paper were categorized according to their chemical mechanism of sensing and were divided into three groups: H2S reducibility-based probes, H2S nucleophilicity-based probes, and metal sulfide precipitation-based probes. The structure of the probes, their sensing mechanism, and imaging results have been discussed in detail. Moreover, we also introduced some probes for hydrogen polysulfides. [ABSTRACT FROM AUTHOR]

Recent reports indicate the ubiquitous prevalence of hydropersulfides (RSSH) in mammalian systems. The biological utility of these and related species is currently a matter of significant speculation. The function, lifetime and fate of hydropersulfides will be assuredly based on their chemical properties and reactivity. Thus, to serve as the basis for further mechanistic studies regarding hydropersulfide biology, some of the basic chemical properties/reactivity of hydropersulfides was studied. The nucleophilicity, electrophilicity and redox properties of hydropersulfides were examined under biological conditions. These studies indicate that hydropersulfides can be nucleophilic or electrophilic, depending on the pH (i.e. the protonation state) and can act as good one- and two-electron reductants. These diverse chemical properties in a single species make hydropersulfides chemically distinct from other, well-known sulfur containing biological species, giving them unique and potentially important biological function.

The kinetics of the coupling of 2‐bromo‐3,5‐dinitrothiophene 1 with various anilines 2a–f were studied in CH3CN at 20°C. The derived second‐order rate constants of anilines possessing an electron‐withdrawing group (e.g., 2d–f) were employed to determine the electrophilicity parameter E of the thiophene 1 according to the correlation equation log k20°C = sN (E + N), where N and sN are nucleophile‐specific parameters. Nonlinear Brønsted and Hammett relationships are discussed, and it is shown that the reactions for donor anilines 2a–d proceed through a single‐electron transfer mechanism. Further support for this assumption was given by the observation that the nucleophilicity parameters N and E° values of oxidation potential constants are linearly related in a direct relationship with a correlation parameter of R2 = 0.9914. The effect of aniline nucleophilicity on reactivity was examined quantitatively on the basis of kinetic measurements, leading to a nonlinear relationship of log (k20°C) with nucleophilicity parameters (N). It is suggested that the observed nonlinear Mayr correlation can be effectively explored to evaluate the nucleophilicity parameters N of four‐substituted aniline radical cations XC6H4NH2+• (X = OH, OMe, Me) and studying their reactivity patterns. On the other hand, it is confirmed that the N values of HOC6H4NH2+• (15.60), MeOC6H4NH2+• (15.23) and MeC6H4NH2+• (14.19) thus obtained can be used to predict the second‐order rate constants for their reactions with N1‐methyl‐4‐nitro‐2,1,3 benzothiadiazolium tetrafluoroborate of known electrophilicity E. This study was one of the first that employed the Mayr approach for determining nucleophilicity parameters of radical cations. [ABSTRACT FROM AUTHOR]

A large number of molecular receptors have been reported for the detection and estimation of cyanide and fluoride ions in chemical, biological, environmental, and industrial processes. The design of such receptors is chiefly linked to specific interaction between them and the target anions. Though hydrogen bond formation is of prime importance, it has been observed that specificity and selectivity of cyanide over fluoride can be achieved by utilizing small size of fluoride and strong nucleophilic but weak basic character of cyanide. Recent results reveal enormous utility of complexation, de-complexation and metallo-supramolecular strategies for the target purpose. These developments signal the advent of more sensitive recognition systems for selecting multi-ion toxicants through a common molecular receptor. This communication scrutinizes results from recent literature on neutral molecular receptors for recognition of cyanide and fluoride ions and elaborates on principles that can be deployed for future developments in the area. [ABSTRACT FROM AUTHOR]

Upon stabilization by 5,6‐bis(diisopropylphosphino)acenaphthene to form compound 1, the fugitive antimony (I) cation exhibited nucleophilic behavior towards coinage metals. Compound 1 was strategically synthesized at room temperature from SbCl3, the bis(phosphine), and trimethylsilyl trifluoromethanesulfonate taken in a 1:2:3 ratio, whereby the bis(phosphine) plays the dual role of a reductant and a supporting ligand. The generation of 1 involves two‐electron oxidation of the ligand to form a P−P bonded diphosphonium dication. Compound 1 was separated from this dication to give both products in pure form in moderate yields. Despite the overall positive charge, the SbI site in 1 was found to bind to metal centers, forming complexes with AuI, AgI and CuI. Compound 1 reduced CuII to CuI and formed a coordination complex with the resulting CuI species. The effects of the electron‐rich bis(phosphine) and the constrained peri geometry in stabilizing and enhancing the nucleophilicity of 1 have been rationalized through computational studies. [ABSTRACT FROM AUTHOR]

In this theoretical survey, we compared and contrasted the substituent influences on stability, aromaticity, band gap, atomic charge distribution, and reactivity of 54 singlet and triplet fused Hammick germylenes derived from germabenzopyridine-4-ylidene as well as the synthesized five- and sixmembered ones by Herrmann and Driess, respectively. Investigations show (1) the lowest and the highest singlet-triplet energy difference (ΔΕs-t) is demonstrated by fusion of two phosphole rings and two furan rings in orthopositions (35.6 and 253.6 kJ/mol, respectively) compared with those of the synthesized germylenes (208.8 and 179.9 kJ/mol, respectively). (2) Whereas fusion of benzene, pyridine, phosphinine, and phosphole rings thermodynamically destabilizes the corresponding germylenes, fusion of pyrrole, furan, and thiophene rings stabilizes the corresponding germylenes. (3) The tendency of substituent influences in number and size of rings is arranged by two fivemembered rings > one five-membered rings > one six-membered rings > two six-membered rings. (4) While pyrrole, furan, and thiophene rings kinetically stabilize the corresponding germylenes, other rings destabilize their germylenes with respect to germapyridine-4-ylidene and the isolated germylene's Driess. (5) All singlet Hammick germylenes reveal lower nucleophilicity and softness, also higher electrophilicity, chemical potential, and global hardness than their scrutinized triplet states. (6) We are waiting for experimental testing and verifications to fuse heterocyclic rings to the germapyridine-4-ylidene's plane in a favorable spatial position to act not only as π-electron giver but also σ-electron receiver. [ABSTRACT FROM AUTHOR]

We have analyzed the electronic structure and bonding situation in monomeric compounds of gallium with group 15 elements (LGa−ECp', L=(CHNMe)2CH, E=N (1), P (2), As (3), Sb (4) and Bi (5)) at the M06/def2‐TZVPP//BP86/def2‐SVP level of theory. The compounds 1–5 have a singlet ground state with a polarized Ga−E double bond. The molecular orbital analysis indicates that the Ga−E π‐MO and the lone pair on E are susceptible to nucleophilic reactivity. The nucleophilic reactivity of Ga−E π‐MO increases, and that of lone pair on E reduces when the compound changes from 1 to 5. The EDA‐NOCV analysis indicates that the nitrogen and phosphorous form charge‐separated electron‐sharing σ‐bond with Ga. The apparent switchover between the electron‐sharing σ‐interaction and donor‐acceptor σ‐interaction occurs when the group 15 element is arsenic. On the other hand, antimony and bismuth exhibit donor‐acceptor interaction with the LGa fragment in compounds 4 and 5. The π‐bond in 1–5 is similar and is formed by the donation of the p‐type lone pair on E‐atom (pz) to the empty pz‐orbital of Ga. The bonding analysis also shows that the strength of π‐bonding is reduced on moving towards the heavier elements. A very high first and second proton affinity indicates that group 15 elements in compounds 1–5 act as double Lewis bases. [ABSTRACT FROM AUTHOR]

We compared and contrasted the ΔΕs-t, band gap (ΔΕHOMO-LUMO), aromaticity, charge distribution, and reactivity of singlet (s) and triplet (t) benzopyridine-4-ylidene as the fused remote N-heterocyclic carbene (frNHC) and frNHSis with different fused aromatic rings, at (U)B3LYP/AUG-cc-pVTZ and (U)M06-2X/AUG-cc-pVTZ levels of theory. In this investigation, we found (1) all s and t divalent states appear as minimum structures, for having no negative force constant. Nonetheless, only singlets present more thermodynamic stability than their triplet analogous; (2) the trend of ΔΕs-t in kcal/mol is ortho-pyrrole (52.94) > ortho-furan (51.84) > ortho-thiophene (50.38) > para-furan (49.36) > para-pyrrole (49.00) > para-phosphole (48.67) ≥ para-thiophene (48.64) > benzene (44.33) > ortho-phosphole frNHSi (27.50), while ΔΕs-t of frNHC is 15.65 kcal/mol; (3) apart from phosphole frNHSis, the order of ΔΕs-t in a "ortho position or zigzag array" about 1.8–4.0 kcal/mol is more than that of in a "para position or chair array"; (4) the highest ΔΕHOMO-LUMO is demonstrated by ortho-pyrrole frNHSi (95.65 kcal/mol) while the lowest ΔΕHOMO-LUMO is verified by the reference frNHC (63.44 kcal/mol); (5) in contradiction of frNHC, all singlet frNHSis reveal higher band gap and lower global reactivity than their triplet congeners; (6) charge distribution along with MEP maps indicate differentially electronic cloud in middle of rings frNHSis vs. frNHC; (7) we anticipate higher nucleophilicity and lower electrophilicity of triplet frNHSis than singlet congeners, will make them worthy of synthetic surveys. [ABSTRACT FROM AUTHOR]

DFT calculations in combination with appropriate isodesmic reactions are employed to assess topological effects of nitrogens on thermodynamic parameters of novel mono-, di-, tri-, tetra-, and pentaaza-7-boratricyclo[1,1,1,01,7,07,3,07,5]hexa-2-silylenes (1–20). Despite the enormous steric strain involved in their cubic structures, all our scrutinized singlet and triplet silylenes (1s-20s vs. 1t-20t, respectively) appear as minima on their energy surfaces, for showing singlet ground states. The highest stability (ΔEs−t) is achieved by 1,3,5-triaza-7-boratricyclo[1,1,1,01,7,07,3,07,5]hexa-2-silylene (11), where all the three nitrogens are bonded to the central boron atom. All of our silylenes show the same trend for their calculated ΔΕs−t and band gap (ΔΕHOMO−LUMO). Isodesmic reactions are employed to compare and contrast nucleophilicity (N), electrophilicity (ω), and heat of hydrogenation (ΔEH) for our 40 silylenes (1s-20s vs. 1t-20t). In fact, we introduce a novel generation of tridimensional silylenes which have the intrinsic potential of expanding the existing boundaries of semiconductors, cumulated multi-dentate ligands, etc.. [ABSTRACT FROM AUTHOR]

• The physicochemical properties of dibenzocine derivatives 1–5 were investigated by DFT method. • The 1H NMR and 13C NMR data of dibenzocine 5 have been used to benchmark the B3LYP/6–311+G(d,p) method. • The DFT results indicated that dibenzocines exhibited a more pronounced interaction with cations possessing smaller atomic radius. • Topological analysis shows that all cation-π interactions within the complexes display positive ∇2 ρ (r). Density functional theory (DFT) calculations are a reliable and fundamental method used to understand the underlying mechanism of antioxidant activity. In this study, we used DFT calculations to explore the structural, electronic, and antioxidant properties of dibenzocine derivatives 1–5. To validate the accuracy of the computational approach, we compared the results with the 1H NMR and 13C NMR data of compound 5 , which served as a benchmark for the B3LYP/6–311+G(d,p) level of theory. Remarkably, the method produced precise outcomes while keeping the computational cost relatively low. We conducted a comprehensive analysis that encompassed various aspects, including chemical potential, HOMO and LUMO energies, electrophilicity, hardness, molecular electrostatic potential profile, and antioxidant capacity of dibenzocine derivatives 1–5. The electrophilicity index of compounds 1–5 ranged from 1.502 to 1.869 in water. Additionally, we employed DFT calculations to investigate the formation mechanism of dibenzocines 1–5. Our findings confirmed that these synthesized compounds possess antioxidant activity, which can be attributed to mechanisms involving hydrogen atom transfer and single electron transfer followed by proton transfer. In the concluding phase of the research, the cation-π interaction between compound 5 and monovalent cations, namely Li+, Na+, K+, and Cu+, was examined using the atoms in molecules analyses and aromaticity indices. The results indicated that compound 5 exhibited a more pronounced interaction with cations possessing smaller atomic radius. [Display omitted] [ABSTRACT FROM AUTHOR]

The α‐effect is a term used to explain the dramatically enhanced reactivity of α‐nucleophiles (R−Y−X:−) compared to their parent normal nucleophile (R−X:−) by deviating from the classical Brønsted‐type reactivity‐basicity relationship. The exact origin of this effect is, however, still heavily under debate. In this work, we have quantum chemically analyzed the α‐effect of a set of anionic nucleophiles, including O‐, N‐ and S‐based normal and α‐nucleophiles, participating in an SN2 reaction with ethyl chloride using relativistic density functional theory at ZORA‐OLYP/QZ4P. Our activation strain and Kohn–Sham molecular orbital analyses identified two criteria an α‐nucleophile needs to fulfill in order to show α‐effect: (i) a small HOMO lobe on the nucleophilic center, pointing towards the substrate, to reduce the repulsive occupied–occupied orbital overlap and hence (steric) Pauli repulsion with the substrate; and (ii) a sufficiently high energy HOMO to overcome the loss of favorable HOMO–LUMO orbital overlap with the substrate, as a consequence of the first criterion, by reducing the HOMO–LUMO orbital energy gap. If one of these two criteria is not fulfilled, one can expect no α‐effect or inverse α‐effect. [ABSTRACT FROM AUTHOR]

We theoretically searched new derivatives of N‐heterocyclic silylenes (NHSis) by substituting of pyridine and phosphinine rings, compared to the reference carbenes (N‐heterocyclic carbenes—NHCs) including benzopyridine‐4‐ylidene (1) and dibenzopyridine‐4‐ylidene (2), at M06‐2X/AUG‐cc‐pVTZ and B3LYP/AUG‐cc‐pVTZ. Regardless of how organized NHSis are, fusion of 1 six‐membered ring leads to more vibration frequency (υmin), stabilizing effect, and polarizability than 2 six‐membered rings. In all cases, singlet (3s‐10s) and triplet (3t‐10t) NHSis emerge as ground state, showing more stability of singlet states than their corresponding triplet congeners. From thermodynamic and kinetic viewpoints, the scrutinized singlet NHSis show more stability than the parent singlet NHCs (1s and 2s), but the studied triplet NHSis exhibit less stability than triplet NHCs (1t and 2t). Regarding the orientation of silylenic center and nitrogen or phosphor heteroatoms of fused rings, the stabilizing energy for para−fused rings is more than ortho ones. The most stability is confirmed by one para−substituted pyridine NHSi (singlet‐triplet energy difference; ΔΕs‐t = 47.3 and band gap; ΔEHOMO‐LUMO = 85.0 kcal/mol; highest occupied molecular orbital [HOMO] and lowest unoccupied molecular orbital [LUMO]) and the least stability is demonstrated by two substituted benzene NHC (ΔΕs‐t = 11.9 and ΔEHOMO‐LUMO = 58.6 kcal/mol). In contrast to pure NHCs, triplet NHSis (3t‐10t) show lower ΔΕHOMO‐LUMO, higher nucleophilicity, lower electrophilicity, and lower chemical hardness than their corresponding singlet states (3s‐10s). [ABSTRACT FROM AUTHOR]

Methyl 12-oxo-6,12-dihydroazepino[2,1-b]quinazoline-8-carboxylate and methyl 3H-azepin-2(1H)-one-5-carboxylate were synthesized by photoinduced heterocyclization of methyl 4-azidobenzoate and ethyl 2-aminobenzoate in the THF–water and acetonitrile-–water mixtures. It was found that the yields of methyl 12-oxo-6,12-dihydroazepino[2,1-b]quinazolate increase with rising water content in the reaction mixture. [ABSTRACT FROM AUTHOR]

The effects of nitrogen substituent on stability (ΔΕs–t) of novel germylenes with one, two, and three germylene centers are compared and contrasted at B3LYP/6‐311++G** level of theory. These singlet and triplet germylenes (1s–18s and 1t–18t, respectively) appear as minimum on its energy surface, and the order of their stability estimated by singlet (s)–triplet (t) energy difference (ΔEs–t = Et − Es) is 16 > 6 > 1 > 15 > 17 > 2 > 8 > 3 > 9 > 11 > 7 > 10 > 12 > 14 > 5 > 4 > 18 > 13. Hence, every singlet germylene shows more stability than its corresponding triplet. Germylene 13 with the lowest stability (ΔEs–t = 4.31 kcal/mol) has the highest nucleophilicity (4.47 eV). Applying suitable isodesmic reactions, we show that the σ‐acceptor nitrogen substituents stabilize not only the singlet but also the triplet states with their positive ΔE. The aim of the present work is to recognize the influence of nitrogen and germylene centers on the stability and band gap (ΔΕHOMO–LUMO), electrophilicity (ω), nucleophilicity (N), and etc. They can be used as accumulated multidentate ligands. [ABSTRACT FROM AUTHOR]

We aim to develop novel four‐membered cyclosilylenes that contain one (1 and 2), two (3), three (4), and four (5) numbers of Si atoms at the M06/6–311 + G*, B3LYP/aug‐cc‐PVTZ, and MP2/3–21G levels of theory. These structures show high stability and turn out as minima on their energy surfaces for showing no imaginary frequency. Structural and thermodynamic parameters, including bond length, divalent bond angle, singlet‐triplet energy gap (ΔES‐T), highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) energy gap (ΔEH‐L), proton affinity (PA), complexation energy (ΔECom) with CO molecule, nucleophilicity (N), chemical potential (μ), and natural charges, are assessed. The final order of singlet stability appears in the order 1 > 2 > 3 > 4 > 5 at three levels of theory. [ABSTRACT FROM AUTHOR]