Electronic Effects Of Substituents Research Articles

Electronic effect of substituents on the charge-transfer dynamics at the CsPbBr3 perovskite-small molecule interface.

To push the boundary of the efficiency of perovskite nanocrystal-based photovoltaics, understanding the charge transfer at the interface of these nanocrystals is necessary. In an effort to understand the electronic effects of the substituents in the charge acceptor moiety, three electronically different small molecules (namely, chloranilic acid (CA), p-benzoquinone (BQ), and duroquinone (DQ)) were chosen and their detailed charge transfer dynamics were studied at the CsPbBr3 perovskite nanocrystal-small organic molecule interface using steady state and time-resolved spectroscopic methods. The steady-state absorption and time-resolved emission studies reveal that all three molecules interact with the NCs in the excited state. Femtosecond transient absorption experiments indicate a faster ground-state bleach recovery in the presence of the three acceptors, compared with the pristine NCs. Utilizing band alignment analysis, the faster bleach recovery of the NCs in presence of the acceptors was confirmed to be because of electron transfer from the photo-excited NCs to the acceptor molecules. Moreover, the electron transfer rates fall in the Marcus normal region and can be explained based on the electronic effects of the substituents present on the acceptor molecules.

Recent progress in tuning charge transport in single-molecule junctions by substituents

We summarized the mechanism of substituent influence on single-molecule conductivity into three aspects: the quantum interference effect, the electronic effect of substituents and the conformational restriction of the conductive backbone.

Vanadium complexes bearing 8-anilide-5,6,7-trihydroquinoline ligands for ethylene (co-)polymerization.

Several trivalent and pentavalent vanadium complexes bearing 8-anilide-5,6,7-trihydroquinoline ligands were synthesized. These vanadium complexes were identified by elemental analysis, FTIR spectroscopy and NMR. Single crystals of trivalent vanadium complexes V2, V3', and V4 and pentavalent vanadium complexes V5 and V7 were further obtained and identified by X-ray single crystal diffraction. In addition, the catalytic performance of these catalysts was adjusted by controlling the electronic and steric effects of substituents in the ligands. In the presence of diethylaluminium chloride, complexes V5-V7 displayed high activity (up to 82.8 × 106 g molV-1 h-1) and good thermal stability toward ethylene polymerization. In addition, the copolymerization ability of complexes V5-V7 was evaluated, and complexes V5-V7 displayed high activity (up to 105.6 × 106 g molV-1 h-1) and high copolymerization ability toward ethylene/norbornene copolymerization. By adjusting the polymerization conditions, copolymers with norbornene insertion ratios of 8.1%-30.9% can be obtained. Complex V7 was further studied for ethylene/1-hexene copolymerization, and the obtained copolymer displayed a moderate 1-hexene insertion ratio of 1.2%. Complex V7 displayed high activity and high copolymerization ability while having thermal stability. The results showed that 8-anilide-5,6,7-trihydroquinoline ligands with fused rigid-flexible rings were beneficial for vanadium catalysts.

Iron(ii) carboxylates and simple carboxamides: an inexpensive and modular catalyst system for the synthesis of PLLA and PLLA-PCL block copolymers.

The combination of inexpensive Fe(ii) acetate with low molecular weight aliphatic carboxamides in situ generates an effective catalyst system for the ring opening polymerisation of lactones. PLLAs were produced in melt conditions with molar masses of up to 15 kg mol-1, narrow dispersity (Đ = 1.03), and without racemisation. The catalytic system was investigated in detail with regard to Fe(ii) source, and steric and electronic effects of the amide's substituents. Furthermore, the synthesis of PLLA-PCL block copolymers of very low randomness was achieved. This commercially available, inexpensive, modular, and user-friendly catalyst mixture may be suitable for polymers with biomedical applications.

Electronic origins of the stereochemistry in β-lactam formed through the Staudinger reaction catalyzed by a nucleophile.

This paper evaluates the electronic effects of molecular substituents on the stereoselectivity of the umpolung Staudinger catalytic reaction. This is especially important because experimental studies on constructing the β-lactam ring, a core structure of most antibiotics, through catalyzed Staudinger reactions have been massively progressing over the last century. Yet, there is a necessity for an in-depth understanding of the reaction mechanisms to help chemists, working on the well-established discoveries, improve these to optimize the stereoselectivity and yield of synthetic methods. Access to practical and effective advancements in forming optically pure β-lactam is paramount in the field of medical chemistry. This paper specifically investigates how changing the N-protecting group in the imine fragment can switch the stereoselectivity of the PPY-catalyzed Staudinger reaction. To do so, we employed the density functional theory (DFT) for geometry optimization and electronic analysis at the B3LYP/6-31G(d) level of theory to examine and compare the role of N-tosyl (N-Ts) and N-triflyl (N-Tf) imine on the mechanism pathways, i.e., imine-first or ketene-first, and stereochemistry of the reaction, i.e., cis or trans β-lactam. Our results show that the reaction mechanism pathway cannot be simply switched from ketene-first to imine-first by changing the substituent on the imine nitrogen atom, which is contrary to the reported experimental results, and both imines go through the ketene-first mechanism with different stereochemistries, which is cis selective for imine-Ts and trans selective for imine-Tf. Based on electronic analyses, the reversal in diastereoselectivity in the N-triflyl imine system could be attributed to the charge transfers and electron-density distribution over the transition states. Therefore, the cis/trans selectivity of the PPY-catalyzed Staudinger reaction could be effectively controlled by the electronic characteristics of the molecular substituents in the reactants. A N-protecting group in imine with a more electron-withdrawing nature seems to accelerate the stereo-determining step, ring closure, and increase the stabilization charge transfers in the transition state, leading to a preference for trans β-lactam formation. It seems that using a N-substituent with a higher electron-withdrawing nature can initially activate the imine by the nucleophilic catalyst in competition with ketene, i.e., imine-first versus ketene-first. These results can provide an insight into select proper substituents for the fragments to synthesis β-lactam with a desired stereochemistry. Also, a comprehensive comparison was performed between calculations with and without dispersion.

Theoretical Study of How Electronic Effect of Substituent Affects Regioselectivity of C—Si Reductive Elimination

Theoretical Study of How Electronic Effect of Substituent Affects Regioselectivity of C—Si Reductive Elimination

ACQ to AIE transformation of quinoline derivatives: modulating substituent electronic effects to alter excited-state reorganization energy distribution

In this manuscript, the conversion of quinoline derivatives from ACQ to AIE was achieved by modulating the quinoline substituents from EDG to EWG.

Synthesis and Characterization of Hypervalent Pentacoordinate Carbon Compounds Bearing a 7-6-7-Ring Skeleton.

To stabilize SN 2 transition state-like penta-coordinate carbon species, triaryl-substituted cationic carbon compounds bearing a moderately flexible 7-6-7-ring skeleton with sulfur donors were synthesized and characterized. Electronic effects of para substituents (R=Cl, F, H, CH3 , SMe, OMe) of the two equatorial aryl groups bound to the cationic central carbon were investigated systematically along with a planar bidentate thioxanthene derivative. X-ray analysis on their solid-state structures showed that the parent (R=H), chloro-, fluoro- and methyl-derivatives were tetracoordinate carbon (sulfonium) structures, while the p-MeO and thioxanthenyl system were pentacoordinate carbocation structures. The Hammett substituent constants for the para substituents (σp + ) correlates well with the bonding in these compounds. The methylthio-derivative with intermediate Hammett substituent constants (p-MeS; σp + =-0.60) showed a tetracooridnate solid-state structure, though solution UV-Vis properties suggested the presence of a penta-coordinate structure. These findings amount to the first unambiguous solution evidence of the hypervalent apical 3c-4e interactions in pentacoordinate carbon compounds.

Electronic Effect‐Modulated Enhancements of Proton Conductivity in Porous Organic Polymers

AbstractWe proposed a new strategy to maximize the density of acidic groups by modulating the electronic effects of the substituents for high‐performance proton conductors. The conductivity of the sulfonated 1‐MeL40‐S with methyl group corresponds to 2.29×10−1 S cm−1 at 80 °C and 90 % relative humidity, remarkably an 22100‐fold enhancement over the nonsulfonated 1‐MeL40. 1‐MeL40‐S maintains long‐term conductivity for one month. We confirm that this synthetic method is generalized to the extended version POPs, 2‐MeL40‐S and 3‐MeL40‐S. In particular, the conductivities of the POPs compete with those of top‐level porous organic conductors. Moreover, the activation energy of the POPs is lower than that of the top‐performing materials. This study demonstrates that systematic alteration of the electronic effects of substituents is a useful route to improve the conductivity and long‐term durability of proton‐conducting materials.

Electronic Effect-Modulated Enhancements of Proton Conductivity in Porous Organic Polymers.

We proposed a new strategy to maximize the density of acidic groups by modulating the electronic effects of the substituents for high-performance proton conductors. The conductivity of the sulfonated 1-MeL40-S with methyl group corresponds to 2.29×10-1 S cm-1 at 80 °C and 90 % relative humidity, remarkably an 22100-fold enhancement over the nonsulfonated 1-MeL40. 1-MeL40-S maintains long-term conductivity for one month. We confirm that this synthetic method is generalized to the extended version POPs, 2-MeL40-S and 3-MeL40-S. In particular, the conductivities of the POPs compete with those of top-level porous organic conductors. Moreover, the activation energy of the POPs is lower than that of the top-performing materials. This study demonstrates that systematic alteration of the electronic effects of substituents is a useful route to improve the conductivity and long-term durability of proton-conducting materials.

Phenolate-Induced N-O Bond Formation versus TiemannType Rearrangement for the Synthesis of 3-Aminobenzisoxazoles and 2-Aminobenzoxazoles.

A novel oxadiazolone-based method for the synthesis of 3-aminobenzisoxazoles by N-O bond formation and of 2-aminobenzoxazoles through a Tiemann-type rearrangement has been developed. The synthesis of these two pharmaceutically relevant heterocycles was realized by an unexplored retrosynthetic disconnection using a cyclic nitrenoid precursor-based strategy. The selective formation of the two isomers was significantly influenced by steric and electronic effects of substituents. However, tetrabutylammonium chloride (TBACl) efficiently promoted the Tiemann-type rearrangement over N-O bond formation. Control experiments indicate that deprotonation of the phenol induces both rearrangements.

Dynamic Hydroxyl-Yne Reaction with Phenols.

Dynamic Covalent Chemistry (DCvC) has gained increasing importance in supramolecular chemistry and materials science. Herein we prove the dynamic nature of the exchange between phenols and vinyl ethers. Exchange is fast at room temperature and under mild conditions. The equilibrium constants and the electronic effect of the phenol substituents were calculated. This novel incorporation to the DCvC toolbox could be quite useful, and as a proof it was used for the synthesis of a responsive molecular cage.

Sodium Aminodiboranates Na(H3BNR2BH3): Structural and Spectroscopic Studies of Steric and Electronic Substituent Effects

We describe the syntheses of a series of sodium aminodiboranate salts, Na(H3B-NR2-BH3), with different substituents on nitrogen, including sodium salts of the unsubstituted aminodiboranate, H3B-NH2-BH3-, and of the N-substituted anions H3B-NRR'-BH3-, where NRR' = NHMe, NHEt, NH(SiMe3), NEt2, N(i-Pr)2, N(SiMe3)2, NMe(i-Pr), NMe(t-Bu), NMe(SiMe3), and the pyrrolidide and piperidide derivatives NC4H8, NC5H10, and NC5H8-cis-2,6-Me2. The compounds have been characterized by 1H and 11B NMR spectroscopy and IR spectroscopy; crystallographic studies have been carried out for the unsolvated N,N-dimethylaminodiboranate salt Na(H3B-NMe2-BH3) and several sodium aminodiboranate salts in which the sodium ions are solvated with ethers (dioxane, diglyme, tetrahydrofuran, and 12-crown-4) or amines (N,N,N',N'-tetramethylethylenediamine). One of the structures contains a rare example of an ether ligand in which one oxygen atom bridges between two metal ions. General structural and spectroscopic trends as a function of the substituents on nitrogen are discussed.

A Comparative Study on the Oxidation Mechanisms of Substituted Phenolic Pollutants by Ferrate(VI) through Experiments and Density Functional Theory Calculations.

In this work, the oxidation of five phenolic contaminants by ferrate(VI) was comparatively investigated to explore the possible reaction mechanisms by combined experimental results and theoretical calculations. The second-order rate constants were positively correlated with the energy of the highest occupied molecular orbital. Considering electronic effects of different substituents, the easy oxidation of phenols by ferrate(VI) could be ranked as the electron-donating group (-R) > weak electron-withdrawing group (-X) > strong electron-withdrawing group (-(C═O)-). The contributions of reactive species (Fe(VI), Fe(V)/(IV), and •OH) were determined, and Fe(VI) was found to dominate the reaction process. Four main reaction mechanisms including single-oxygen transfer (SOT), double-oxygen transfer (DOT), •OH attack, and electron-transfer-mediated coupling reaction were proposed for the ferrate(VI) oxidation process. According to density functional theory calculation results, the presence of -(C═O)- was more conducive for the occurrence of DOT and •OH attack reactions than -R and -X, while the tendency of SOT for different substituents was -R > -(C═O)- > -X and that of e--transfer reaction was -R > -X > -(C═O)-. Moreover, the DOT pathway was found in the oxidation of all four substituted phenols, indicating that it may be a common reaction mechanism during the ferrate(VI) oxidation of phenolic compounds.

Novel Strategy for Non-Aqueous Bioconjugation of Substituted Phenyl-1,2,4-triazole-3,5-dione Analogues.

A novel 4-[4-(pentafluoro-λ⁶-sulfanyl)phenyl]-1,2,4-triazole-3,5-dione (5a) was synthesised as a potential [18F]radio-prosthetic group for radiolabelling peptides and proteins via selective bioconjugation with the phenolic side chains of tyrosine residues. Preliminary conjugation tests revealed the rapid hydrolysis of 5a under semi-aqueous conditions; these results led to further investigation into the electronic substituent effects of PTAD derivatives and corresponding hydrolytic stabilities. Five derivatives of 5a with para substituents of varying electron donating and withdrawing effects were synthesised for the investigation. The bioconjugation of these derivatives with model tyrosine was monitored in both aqueous and organic media in the presence of a variety of catalysts. From these investigations, we have found HFIP to be an effective catalyst when used in tandem with DCM as a solvent to give PTAD-tyrosine conjugate products (6a–f) in satisfactory to good yields (54–79%), whereas analogous reactions performed in acetonitrile were unsuccessful. The discovery of this system has allowed for the successful conjugation of electron-deficient PTAD derivatives to tyrosine, which would otherwise be unachievable under aqueous reaction conditions. The inclusion of these electron-deficient, fluorinated PTAD derivatives for use in the PTAD-tyrosine conjugation will hopefully broaden their applicability within fields such as 19F-MRI and PET imaging.

Iron-Catalyzed Cross-Electrophile Coupling of Inert C–O Bonds with Alkyl Bromides

Iron-Catalyzed Cross-Electrophile Coupling of Inert C–O Bonds with Alkyl Bromides

Carbonate-induced enhancement of phenols degradation in CuS/peroxymonosulfate system: A clear correlation between this enhancement and electronic effects of phenols substituents

This study investigated the enhancement effects of dissolved carbonates on the peroxymonosulfate-based advanced oxidation process with CuS as a catalyst. It was found that the added CO32− increased both the catalytic activity and the stability of the catalyst. Under optimized reaction conditions in the presence of CO32−, the degradation removal of 4-methylphenol (4-MP) within 2 min reached 100%, and this was maintained in consecutive multi-cycle experiments. The degradation rate constant of 4-MP was 2.159 min−1, being 685% greater than that in the absence of CO32− (0.315 min−1). The comparison of dominated active species and 4-MP degradation pathways in both CO32−-free and CO32−-containing systems suggested that more CO3•−/1O2 was produced in the case of CO32−deducing an electron transfer medium, which tending to react with electron-rich moieties. Meanwhile, Characterization by X-ray photoelectron spectroscopic and cyclic voltammetry measurement verified CO32− enabled the effective reduction of Cu2+ to Cu+. By investigating the degradation of 11 phenolics with different substituents, the dependence of degradation kinetic rate constant of the phenolics on their chemical structures indicated that there was a good linear relationship between the Hammett constants σp of the aromatic phenolics and the logarithm of k in the CO32−-containing system. This work provides a new strategy for efficient removal of electron-rich moieties under the driving of carbonate being widely present in actual water bodies.

Tuning cationic transport in Nisalen polymers via pseudo-crown functionality

Polymeric films based on nickel complexes with salen-type ligands have received considerable attention recently owing to electrocatalytic, electrochromic, and charge storing properties. The latter makes them suitable metal-organic materials for electrochemical power sources, i.e., batteries and supercapacitors. Optimization of the properties of electrode materials is closely linked to the understanding of charge storage mechanisms. The introduction of CH3O substituent into the molecule results in peculiar ionic transport mechanism, owing to the possibility of alkaline ions coordination. Here we study the recharging mechanism of poly[Ni(CH3Osalen)] films in various electrolyte solutions. In presence of alkali ions, the electronic effects of methoxy substituent provide mixed anionic and cationic charge compensation mechanism, as cations reversibly coordinate to the present pseudo-crown functionality. By applying the combination of XRD, CV/EQCM and EIS methods to the film in electrolytes containing Li+, Na+, K+, and Et4N+ cations, and BF4−, ClO4− and bistrifluoromethanesulfonimidate (TFSI−) anions, we propose a model that describes the ionic transport in such polymeric films and allows to estimate the anionic and cationic contribution to the total amount of transferred species during charging and discharging.

Substituent Control of Near-Infrared Absorption of Triphenylamine Radical Cation

Five triphenyltriphenylamines with various substituents were investigated as precursors for near-infrared absorbing materials. Cyclic voltammetry (CV) studies showed that they all give stable radical cations in solution. The radical cations obtained by one-electron chemical oxidation of these compounds show strong absorption in the near-infrared region, and the position of the absorption is strongly influenced by the substituent. DFT (density functional theory) calculations suggest that the introduction of stronger electron-donating substituents would result in a smaller HOMO–SOMO energy gap and thus a larger long wavelength shift, which is consistent with the experimental results. On the other hand, strong electron-withdrawing substituents increase the HOMO–SOMO energy gap, resulting in a short wavelength shift. The position of the near-infrared absorption peak of the triphenylamine radical cation can be controlled to the longer or shorter wavelength direction depending on the substituent. A molecular design of near-infrared absorbing dyes utilizing the electronic effects of substituents is described.

Effect of Substituents on the Homopolymerization Activity of Methyl Alkyl Diallyl Ammonium Chloride.

Among nitrogen-containing cationic electrolytes, diallyl quaternary ammonium salt is a typical monomer with the highest positive charge density, which has attracted the most attention, especially in the research on homopolymers and copolymers of dimethyl diallyl ammonium chloride (DMDAAC), which occupy a very unique and important position. In order to improve the lipophilicity of substituted diallyl ammonium chloride monomers under the premise of high cationic charge density, the simplest, most direct, and most efficient structure design strategy was selected in this paper. Only one of the substituents on DMDAAC quaternary ammonium nitrogen was modified by alkyl; the substituents were propyl and amyl groups, and their corresponding monomers were methyl propyl diallyl ammonium chloride (MPDAAC) and methyl amyl diallyl ammonium chloride (MADAAC), respectively. The effect of substituent structure on the homopolymerization activity of methyl alkyl diallyl ammonium chloride was illustrated by quantum chemical calculation and homopolymerization rate determination experiments via ammonium persulfate (APS) as the initiator system. The results of quantum chemistry simulation showed that, with the finite increase in substituted alkyl chain length, the numerical values of the bond length and the charge distribution of methyl alkyl diallyl ammonium chloride monomer changed little, with the activation energy of the reactions in the following order: DMDAAC < MPDAAC < MADAAC. The polymerization activities measured by the dilatometer method were in the order DMDAAC > MPDAAC > MADAAC. The activation energies Ea of homopolymerization were 96.70 kJ/mol, 97.25 kJ/mol, and 100.23 kJ/mol, and the rate equation of homopolymerization of each monomer was obtained. After analyzing and comparing these results, it could be easily found that the electronic effect of substituent was not obvious, whereas the effect of the steric hindrance was dominant. The above studies have laid a good foundation for an understanding of the polymerization activity of methyl alkyl diallyl ammonium chloride monomers and the possibility of preparation and application of these polymers with high molecular weight.