Electronic Effects Of Substituents Research Articles

Structural Analysis of 3,5-Bistrifluoromethylhydrocinnamic Acid

The crystal structure of 3,5-bistrifluoromethylhydrocinnamic acid [systematic name: 3-[3,5-bis(trifluoromethyl)phenyl]propanoic acid], C11H8F6O2, has been determined and described. The structure was subject to the Hirshfeld surface-analysis and CE-B3LYP interaction-energies calculations. The title compound crystallises in the monoclinic P21/c space group with one molecule in the asymmetric unit. The propanoic acid side chain of the studied molecule has a bent conformation. The key supramolecular motif in the crystal structure is a centrosymmetric O–H∙∙∙O hydrogen-bonded dimer (R22(8) in the graph set notation). According to CE-B3LYP, the molecules involved in this motif exhibit the strongest pairwise interaction total energy (Etot = −67.9 kJ/mol). On the other hand, there are seven other interacting molecular pairs with significant Etot values in the range of −17 to −28 kJ/mol. In these, the energy is dominated by the dispersive contribution. A survey of the Cambridge Structural Database revealed that in other 3-phenylpropanoic acid structures, the middle dihedral angle of the propanoic acid side chain is always in the trans conformation. This contrasts the current structure where this dihedral angle is in the gauche conformation. According to the Density Functional Theory calculations in the gas phase (at the B3LYP/aug-cc-pvDZ level), the presence of the two CF3 groups (strong electron-withdrawing character) increases the population of the gauche conformers by a substituent electronic effect, and this may be a minor factor contributing to the appearance of this conformation observed in the solid state.

Effects of additional ring-fusion site on dual reactivity based dynamic covalent chemistry

Tautomers are widespread in organic chemistry, and their unique reactivity allows diverse transformations. In this work, the incorporation of nearby amide ring-fusion site offered a versatile platform for controlling dual reactivity based dynamic covalent chemistry (DCC) of aldehyde ring-chain tautomers. A suite of 2-formylbenzosulfonamide derived tautomers were prepared, and the intramolecular ring-chain equilibrium and intermolecular dynamic covalent reactions along the underlying mechanistic foundation were investigated. By regulating the substituent electronic effect and solvent effect, ring-chain tautomerization equilibrium was readily regulated in solution. The adjacent amide NH participates in intramolecular hydrogen bonding, as revealed by crystal analysis. Furthermore, the addition of acid and the change of solvent allowed turning on/off the intramolecular cyclization from the amide group to create fused ring scaffolds. Finally, the reversible covalent reactions with amine nucleophile reagents maintained the intermolecular reactivity successfully. The molecular and pathway diversity reported herein sets the scene for future design and applications.

Ethylene/Polar Monomer Copolymerization by [N, P] Ti Complexes: Polar Copolymers with Ultrahigh-Molecular Weight.

A series of novel titanium complexes (2a-2e) bearing [N, P] aniline-chlorodiphenylphosphine ligands (1a-1e) featuring CH3 and F substituents have been synthesized and characterized. Surprisingly, in the presence of polar additive, the complexes (2a-2e) all displayed high catalytic activities (up to 1.04 × 106 gPolymer (mol·Ti)-1·h-1 and produced copolymer with the ultrahigh molecular weight up to 1.37 × 106 g/mol. The catalytic activities are significantly enhanced by introducing electron-withdrawing group (F) into the aniline aromatic ring. Especially, the increase in activity based on different complexes followed the order of 2e > 2d > 2c > 2b > 2a. Simultaneously, density functional theory (DFT) calculations have been performed to probe the polymerization mechanism as well as the electronic and steric effects of various substituents on the catalyst backbone. DFT computation revealed that the polymerization behaviors could be adjusted by the electronic effect of ligand substituents; however, it has little to do with the steric hindrance of the substituents. Furthermore, theoretical calculation results keep well in accordance with experimental measurement results. The article provided an appealing design method that the employment of fluorine atom as electron-withdrawing to be studied is the promotive effect of transition-metal coordination polymerization.

Adjusting UV-Vis Spectrum of Alizarin by Insertion of Auxochromes.

First synthesized in 1868, alizarin became one of the first synthetic dyes and was widely used as a red dye in the textile industry, making it more affordable and readily available than the traditional red dyes derived from natural sources. Despite extensive both experimental and computational analyses on the electronic effects of substituents on the shape of the visible spectrum of alizarin and alizarin Red S, no previous systematic work has been undertaken with the aim to fine tune the dominant absorption region defining its color by introducing other electron-withdrawing or electron-donor groups. For such, we have performed a comprehensive study of electronic effects of substituents in position C3 of alizarin by means of a time dependent DFT approach. These auxochromes attached to the chromophore are proven to alter both the wavelength and intensity of absorption. It is shown that the introduction of an electron-donor group in alizarin causes the transition bands to be significantly red-shifted whereas electron-withdrawing groups cause a minor blue-shifting.

Substituent effects on the selectivity of ambimodal [6+4]/[4+2] cycloaddition.

In this work, we report a density functional theory (DFT) study and a dynamical trajectory study of substituent effects on the ambimodal [6+4]/[4+2] cycloaddition proposed for 1,3,5,10,12-cycloheptadecapentaene, referred to as cycloheptadecapentaene. The proposed cycloaddition proceeds through an ambimodal transition state, which results in both a [6+4] adduct a [4+2] adduct directly. The [6+4] adduct can be readily converted to the [4+2] adduct via a Cope rearrangement. We study the selectivity of the reaction with regard to the position of substituents, steric effects of substituents, and electronic effects of substituents. In the dynamical trajectory study, we find that nitro-substituted reactants lead to a new product from the ambimodal transition state via the hetero Diels-Alder reaction, and this new product can then be converted to a [4+2] adduct by a hetero [3, 3]-sigmatropic rearrangement. These results may provide insights for designing more bridged heterocyclic compounds.

Electronic substituent effect on the conformation of a phenylalanine-incorporated cyclic peptide.

The Phe-incorporated cyclic peptide [cyclo(-Phe1-oxazoline2-d-Val3-thiazole4-Ile5-oxazoline6-d-Val7-thiazole8-)] is in a conformational equilibrium between square and folded forms in solution. In the folded form, a CH⋯π interaction between the Phe1 aromatic ring and the Oxz2 methyl group is observed. We endeavored to control the local conformation and thus modulate the CH⋯π interaction and flexibility of the Phe1 side chain by controlling the electronic substituent effects at the 4-position of the aromatic ring of the Phe1 residue. The effect of the 4-substituent on the global conformation was indicated by the linear relationship between the conformational free energies (ΔGo) determined through NMR-based quantification and the Hammett constants (σ). Electron-donating substituents, which had relatively strong CH⋯π interactions, promoted peptide folding by restraining the loss in entropy. Local control by the 4-substituent effects suggested that the Phe side chain exerts an entropic influence on the folding of these cyclic peptides.

Insight into the Chemical Stability of N-Heterocyclic Ammonium Groups for Anion-Exchange Polyelectrolytes

The chemical stability of cationic groups, not only related to alkaline degradation but also to electrochemical degradation at high potentials, is the key factor that limits the durability of anion exchange membranes (AEMs) and anion exchange ionomers (AEIs) [1]. In recent years, quaternary ammonium (QA) groups represented by N-heterocyclic ammonium (NHA) groups display excellent ionic conductivity and superior alkaline stability, which makes NHA groups promising candidates to be applied in AEMs and AEIs [2]. However, electrochemical degradation of NHA groups has been neglected in previous research, even though the electrochemical oxidation of phenyl QAs was found in the ionomer at the oxygen evolution potentials [3]. In short, the mechanism by which effect of substituents affects the durability of NHAs cations, including alkaline stability and electrochemical stability, is unclear yet, and NHA groups must be attached to the polymer backbones by substituents to achieve their applications.In this work, the chemical stability of NHA is comprehensively studied. To investigate the relationship between alkaline durability and structure, we report a systematic study on the alkaline stability of 24 representative NHA groups at different hydration numbers (λ). The electronic effect of substituents on NHA groups and degradation mechanisms of NHA groups are systematically investigated by 1H nuclear magnetic resonance (1H NMR) and density functional theory (DFT) calculations, showing that the NHA groups with electron-donating substituents exhibit outstanding alkaline stability and linking NHA groups with the polymer backbone via γ-position could be a rational design for highly alkaline stable AEMs and AEIs. Furthermore, a constant voltage is applied to the QAs electrolyte solution to measure the electrochemical stability by simulating the real operating environment of and AEM water electrolyzers. Compared to structural changes before and after voltage application, NHA exhibits worse stability than alkyl QAs, involving the radical degradation and electrochemical degradation. These results above give us a clearer picture while designing the polymer used for electrochemical devices, which is that a careful balance needs to be established between alkaline and electrochemical durability, especially under the high potential and harsh alkaline environment.

Electronic and steric substituent effects on the fluorescence emission of 2-pyrazoline derivatives.

A series of substituted 2-pyrazolines were synthesized, and the steric and electronic effects of substituents on the C3 - and C5 -positions of the heterocyclic ring on their fluorescent ability were investigated. Two different conjugative intramolecular charge transfer (ICT) and intramolecular charge transfer through space (spiro-conjugation) affect the fluorescence intensity of these compounds. The extent of the ICT process and spiro-conjugation depends on the electronic nature of the additional substitution and its position on the attached aryl rings. In addition, the effects of the concentration and the solvent polarity on the fluorescence emission were studied. Density functional theory (DFT) calculations were carried out to gain insight into the geometric, electronic, and spectroscopic properties of the pyrazoline derivatives. The results of both experimental and computational studies explain the effects of the geometrical orientation of the C3 - and C5 -aryl rings toward the heterocyclic ring and also the electronic nature of their additional substitutions on the fluorescence intensity.

A new method for determining the intrinsic resistance energy of H‐atom transfer reaction and structure–activity relationship of H‐donating ability

AbstractThe intrinsic resistance energy ΔG≠XH/X of H‐donor XH in hydrogen atom transfer (HAT) reaction is usually used to evaluate the kinetic H‐donating ability. In this article, a new method for determining ΔG≠XH/X of H‐donor in HAT reaction was proposed by the definition of thermo‐kinetic parameter ΔG≠o (XH) = 1/2[ΔG≠XH/X + ΔGo (XH)]. ΔG≠o (XH) is the characteristic physical parameter of XH to describe the H‐donating ability in a chemical reaction during a certain reaction time, ΔGo (XH) is the bond dissociation free energy. The kinetic studies of HATs between 20 alcohols, ethers, alkanes and amines (XH) with cumyloxyl radical [PhC (CH3)2O•, CumO•] were researched, and ΔGo (XH), ΔG≠XH/X, and ΔG≠o (XH) were used to investigate the H‐donating abilities of the studied substrates in thermodynamics, kinetics, and HAT reaction. The effect of structures of XH on these three parameters, the structure–activity relationship, such as the influence of electronic, steric, polar and stereoelectronic effects of substituents, heteroatoms insertion in cycloalkanes, and cis–trans configurational isomerism on the H‐donating abilities were discussed in detail. This study not only provides a new method for determining ΔG≠XH/X but also systematically studies the factors affecting the H‐donating ability, laying a foundation for the selection, design, and synthesis of more efficient antioxidants.

Hydrogen-Bonding-Assisted Substituent Engineering for Modulating Magnetic Spin Couplings and Switching in m-Phenylene Nitroxide Diradicals.

Rational modification of the coupler for the theoretical design of molecular magnets has attracted extensive interest. Substituent insertion is a widely used strategy for adjusting molecular properties, but its effect and modulation on magnetic spin couplings have been less investigated. In this work, we predict the magnetic properties of the design m-phenylene nitroxide (NO) diradicals regulated by introducing substituents. The calculated results for those two pairs of diradicals indicate that the signs of their magnetic coupling constants J do not change, but the magnitudes remarkably change after substituent regulation in the range from 253 to 730 cm-1. Such noticeable magnetic changes induced by introducing subsituents are mainly attributed to different electronic effects of substituents, assisted by the proximity of two NO groups, good planarity, conjugation, and an intramolecular hydrogen bond. In particular, the insertion of intramolecular H-bonds not only indicates an electronic effect but also has greatly changed the spin density distribution. Further aromaticity of the coupler ring, spin densities, and molecular orbitals and energetics was evaluated to gain a better understanding of magnetic regulation. Interestingly, further protonation of some substituents (e.g., -NO2 and -CO2) can noticeably turn the spin coupling from ferromagnetic to antiferromagnetic, showing manipulable magnetic switching. This work provides a promising strategy based on substituent engineering for magnetic spin coupling modulation, not only turning the coupling magnitude but also enabling the magnetic switching, thus providing insights into molecular magnetic manipulation for spintronics applications.

Electrochemistry of Polyfluorinated Organic Molecules in Nonaqueous Electrolyte Solutions

Fluoroorganic molecules provide significant benefit for many applications including pharmaceuticals, agrichemicals, and advanced functional materials due to its highly stable carbon fluorine bonds. Fluorination can have profound effects upon tuning the electronic and optical properties of organic molecules. Thus, fluorine is found in many state-of-the-art materials. For example, fluorinated liquid crystals are used for active-matrix liquid crystal displays; fluorinated membranes are utilized as proton transfer elements necessary for the function of fuel cells; fluorinated electrolyte solutions are tested in lithium batteries to improve their long-term stability and cell voltage. Lately, fluorinated and perfluoroalkylated organic semiconductors were reported for its application in organic field effect transistors (OFETs). Fluorination can tune a p-type organic semiconductor into an n-type semiconductor because of the strong electron withdrawing effect of fluorine, though use of multiple fluorine substituents directly on the aromatics or use of trifluoromethyl and perfluoroalkyl substituents on the pi system is essential for such conversion.The high electronegativity of fluorine results in exceptionally strong bonds to carbon (BDE = 110-126 kcal/mol). Moreover, fluorine substitution results in an increase in the C-C bond energy in fluorocarbons. Strong C-F and corresponding strong C-C bonds in fluorocarbons make them less polarizable than typical hydrocarbons. The highly polar, weakly polarizable, non-hydrogen bonding, non-coordinating properties of perfluoroalkylated materials and perfluoropolyether materials, underlie the motto “Nothing sticks to Teflon® and Teflon®-coated products”. Though all these profound properties of fluoroorganics paved the road for applications exemplified above, their superior stability creates significant challenges for their end-of-life recycling and repurposing, as well as remediation of environmental persistent fluoroorganics such as PFAS. Furthermore, the chemical stability of many these materials often refers to the stability under oxidizing conditions. For fluorinated n-type organic semiconductor materials and fluorinated solvents (e.g. fluoroethylene carbonate) in lithium battery applications, access the stability of these materials and understand its decomposition mechanism under reductive conditions are necessary for rationally optimize the conditions for such applications.In this presentation, we will present and discuss our latest electrochemical study of several different types of polyfluorinated organic molecules involving both fluorinated and perfluoroalkylated aromatics, as well as inert hydrofluorocarbons where only sp3-hybridized carbon presents. As an example, our electrochemical and computational chemistry results indicate that aromatic trifluoromethlation is likely a more stable option against reduction than pentafluoroethylation of the same aromatic core, though the electronic effects of trifluoromethyl and pentafluoroethyl substituents on aromatics are almost identical. We hope that these electrochemical results will shine some lights on searching new materials for electronic and energy storage applications and repurposing inert hydrofluorocarbons, for example, pentafluoroethane, a refrigerant with high global warming potential to be phased out in the next 10-20 years.

Quinoline-derived electron-donating/withdrawing fluorophores for hydrazine detection and applications in environment and bioimaging

Substitution can be employed to competently tune the photophysical properties of chemosensors. The effect of substituents on the absorption and emission properties of quinoline probes was investigated. Therefore, salicylaldehyde (S), N-diethylamino-salicylaldehyde (D), and nitro-salicylaldehyde (W)-based quinoline Schiff base derivatives were investigated with hydrazine and studied for their photophysical properties. The nucleophilic substitution reaction was used as a sensing mechanism between the probes and hydrazine and investigated with 1H NMR, HR-MS characterizations, and DFT calculations. The sensitivity of QW-R is greater than that of QS-R and QD-R because of the stronger intramolecular charge transfer (ICT) in QW-R. The calculated LOD values are 28 nM for QS-R, 30 nM for QD-R, and 9 nM for QW-R. The probes were employed to monitor gaseous hydrazine using a smartphone and analyze solution forms of hydrazine in soil, water, and food samples, and living cells. Moreover, the in situ hydrazine release was monitored with bioimaging by administering an isoniazid drug. Significantly, the electronic effect of substituents over fluorescence showing, ranging from electron-donating to electron-withdrawing was investigated. We anticipate that this approach may be a promising strategy for the rational design of fluorescent sensors.

Synthesis of new efficient fluorophores of thieno[2,3-<i>b</i>]pyridine series

The reaction of 4-amino-6-aryl-2-halopyridine-3,5-dicarbonitriles with thioglycolic acid ethyl ester was used to synthesize a series of new efficient fluorophores of thieno[2,3- b ]pyridine series. The long-wavelength absorption bands of DMSO solutions of the prepared compounds are at the boundary of the UV and visible regions of the spectrum (λabs 375-388 nm) and show an ambiguous influence of the substituent electronic effect, that was explained by quantum chemical calculations. The emission maxima are in the yellow-green region (λem 490- 510 nm) and they are blue-shifted in the presence of electron donor groups with slightly increasing intensity (Φem 37.8-60.6%). It was found that the nitro group presence causes a complete photoluminescence quenching both in solution and in the solid state. In addition, the position of the emission maximum (λem 473-505 nm) and its intensity (Φem 3.6-72.7%) strongly depend on the polarity and the basic properties of the medium, that was established using the Catalan empirical model.

Dichotomic Dearomatizations of Benzene vs Pyridine Rings of Sulfonyloxypyridine via (3 + 2) Cycloaddition.

Electron-poor arenesulfonyloxypyridines are selectively dearomatized whether on the pyridine or on the phenyl group through 1,3-dipolar cycloaddition (1,3-DC) involving non-stabilized azomethine ylides (AMY). Electronic effects of substituents on the aromatic rings allow to induce the regioselectivity of the transformation. Novel pyrrolidinic polycyclic heterocycles are thereby produced under mild acidic conditions at room temperature.

The Electronic Effects of 3-Methoxycarbonylcoumarin Substituents on Spectral, Antioxidant, and Protein Binding Properties.

Coumarin derivatives are a class of compounds with pronounced biological activities that depend primarily on the present substituents. Four 3-methoxycarbonylcoumarin derivatives with substituents of different electron-donating/electron-withdrawing abilities (Br, NO2, OH, and OMe) were investigated structurally by NMR, IR, and UV-VIS spectroscopies and density functional theory methods. The appropriate level of theory (B3LYP-D3BJ/6-311++G(d,p) was selected after comparing similar compounds' experimental and theoretical structural parameters. The natural bond orbital and quantum theory of atoms in molecules were employed to investigate the intramolecular interactions governing stability. The electronic effects of substituents mostly affected the aromatic ring that the substituents are directly attached to. The antioxidant properties were investigated by electron paramagnetic resonance spectroscopy towards HO•, and the percentages of reduction were between 13% (6-Br) and 23% (6-OMe). The protein binding properties towards transport proteins were assessed by spectrofluorimetry, molecular docking, and molecular dynamics (MD). The experimentally determined binding energies were well reproduced by molecular docking, showing that the spontaneity of ibuprofen binding was comparable to the investigated compounds. The flexibility of HSA in MD simulations depended on the substituents. These results proved the importance of electronic effects for the protein binding affinities and antioxidant properties of coumarin derivatives.

2-Arylbenzo[d]xazolyl based iridium(III) complexes as highly efficient photoredox catalysts

The [Ir(C^N)2(N^N)]+ complexes are one of the most employed family of photocatalyst. The substituent effect of C^N ligand, specifically 2-arylbenzo[d]oxazole (pbo) and 2-arylbenzo[d]thiazole (pbt), on complexes was discussed in this work. For this purpose, a series of Ir(III) complexes (A1∼C9) with differently substituted pbo/pbt ligands were designed, synthesized and characterized. Crystal structures show that A2 and A6 have a C2-symmetric trans-configuration while B8 possesses C1-symmetric cis-isomeric structure. These complexes are highly photoluminescent with quantum yield up to 69% in dilute solution. The maximum emission wavelength span from 485 to 615 nm. The substituent electronic effects on the para-position of phenyl have the greatest impact on the fluorescence properties of the complexes. Electron withdrawing nitro group on the 4-site of phenyl make the greatest red shift in the emission spectra while fluorination leads to blue shifts. The electrochemical measurements were combined with fluorescence data to estimate the excited-state potentials (ESP) of these complexes. Both oxidative and reductive ESP are in a good range compared to the widely applied [Ir(dF(CF3)ppy)2dtbbpy]PF6, suggesting that they are high-potential in photoredox catalysis. The complexes A1∼C9 were further applied in the deoxygenation-addition synthesis of N-dimethyl-4-oxo-4-(p-tolyl)butanamide to test the catalytic activity. Excellent yields (up to 91%) were obtained with catalyst A2, A8 and B8. Substitution on substrates was also tolerated in a degree.

High‐Contrast Optical Nitrile‐Rich Molecular Switches: Synthesis of Pyrrol‐2‐ones Containing a Butadienetricarbonitrile Fragment and Kinetics of Their Reversible Interaction with Morpholine

AbstractDirect synthesis of previously undescribed 5‐aryl‐substituted pyrrol‐2‐one derivatives containing a butadienetricarbonitrile (BDTC) acceptor was carried out. The kinetics of their reversible interaction with morpholine accompanied with high‐contrast color changes in acetonitrile solution was studied for the first time. It was found that the electronic effects of substituents in aromatic ring had a direct effect on the reaction rate and extent, that was supported by the observed linearity between the estimated equilibrium constants and the electrophilic Hammett constants.

Electronic structure and spatial hindrance effects of substituents on mechanical force-induced fluorescent response of xanthone derivatives with terminal carbazole or triphenylamine groups

Two novel D-A type luminophores XAO-Cz and XAO-TPA, in which xanthone as the electron-withdrawing and carbazole or triphenylamine as the electron donating, were designed and synthesized using Suzuli-Miyaura coupling reaction. Optical research and theoretical calculation indicated that both compounds exhibited a twisted molecular conformation as well as strong intramolecular charge transfer (ICT) characteristics. Moreover, XAO-Cz and XAO-TPA also exhibited fluorescent response to mechanical force with wavelength redshifts of 14 nm and 48 nm, respectively. To the best of our knowledge, this is the first example based on xanthone derivatives exhibiting fluorescent response to mechanical force. It is worth noting that XAO-TPA showed more significant mechanochromism than those of XAO-Cz. The reason may be due to strong ICT transition, highly twisted conformation and weak intermolecular interaction. The current work provided effective strategy at the molecular level to achieve high contrast fluorescent response to mechanical force.

Electronic effects of substituents on the reactivity of silenes: a computational analysis

Electronic effects of substituents on the reactivity of silenes: a computational analysis

Selective photocatalytic oxidation of aromatic alcohols using B-g-C3N4/Bi2WO6 composites

In this work, B-g-C3N4/Bi2WO6 composites were synthesized by simple hydrothermal reaction and calcination, and their morphology, composition and physicochemical properties were characterized. The results show that the composite can selectively oxidize aromatic alcohols to aromatic aldehydes under visible light. The conversion rate of benzyl alcohol can reach 98.9% and the selectivity can reach 99% in 4 h, which are 1.59 times and 5.03 times that of Bi2WO6 alone, respectively. Further photoelectric performance investigation revealed that the recombination of B-g-C3N4 with Bi2WO6 effectively enhanced the separation of photogenerated carriers of B-g-C3N4 and suppressed the generation of holes on Bi2WO6, thereby improving the photocatalytic activity and the selectivity of the catalytic reaction of p-benzyl alcohol. In addition, the electronic effect and steric hindrance effect of substituents on the benzene ring on the selective catalytic oxidation of aromatic alcohols were also explored. Our work also reveals that the bandgap structure of the composites and the efficient separation of photogenerated electron transport are key factors to improve the photocatalytic reactivity and selectivity of organic reactions.