Role of methoxy and C_(α)-based substituents in electrochemical oxidation mechanisms and bond cleavage selectivity of β-O-4 lignin model compounds

In order to better understand the specific substituent effects on the electrochemical oxidation process of β-O-4 bond, a series of methoxyphenyl type β-O-4 dimer model compounds with different localized methoxyl groups, including 2-(2-methoxyphenoxy)-1-phenylethanone, 2-(2-methoxyphenoxy)-1-phenylethanol, 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)ethanone, 2-(2-methoxyphenoxy)-1-(4-methoxyphenyl)ethanol, 2-(2,6-dimethoxyphenoxy)-1-(4-methoxyphenyl)ethanone, 2-(2,6-dimethoxyphenoxy)-1-(4-methoxyphenyl)ethanol have been selected and their electrochemical properties have been studied experimentally by cyclic voltammetry, and FT-IR spectroelectrochemistry. Combining with electrolysis products distribution analysis and density functional theory calculations, oxidation mechanisms of all six model dimers have been explored. In particular, a total effect from substituents of both para-methoxy(on the aryl ring closing to Cα) and Cα-OH on the oxidation mechanisms has been clearly observed, showing a significant selectivity on the Cα-Cβbond cleavage induced by electrochemical oxidations.

Tetrathiafulvalene esters with high redox potentials and improved solubilities for non-aqueous redox flow battery applications

The exploitation of high performance redox-active substances is critically important for the development of non-aqueous redoxflow batteries.Herein,three tetrathiofulvalene(TTF)derivatives with different substitution groups,namely TTF diethyl ester(TTFDE),TTF tetramethyl ester(TTFTM),and TTF tetraethyl ester(TTFTE),are prepared and their energy storage properties are evaluated.It has been found that the redox potential and solubility of these TTF derivatives in conventional carbonate electrolytes increases with the number of ester groups.The battery with a catholyte of 0.2 mol L^(-1) of TTFTE delivers a specific capacity of more than 10 Ah L^(-1) at the current density of 0.5 C with two discharge voltage platforms locating at as high as 3.85 and 3.60 V vs.Li/Liþ.Its capacity retention can be improved from 2.34 Ah L^(-1) to 3.60 Ah L^(-1) after 100 cycles by the use of an anion exchange membrane to block the crossover of TTF species.The excellent cycling stability of the TIF esters is supported by their well-delocalized electrons,as revealed by the density function theory calculations.Therefore,the introduction of more and larger electron-withdrawing groups is a promising strategy to simultaneously increase the redox-potential and solubility of redox-active ma-terials for non-aqueous redoxflow batteries.

Effects of Bases on the Stabilities of Nucleoside C4'Radicals

C4'-H bond dissociation enthalpies of nucleosides were predicted using theoretical methods to a precision of 1-2 Kcal/mol. It was found that the stability of the C4' nucleoside radical is slightly dependent on the base. The orders of stability are dA < dG < dT < dC for deoxynucleosides and U < G < A = C for nucleosides.

POLAR SUBSTITUENT EFFECTS OF ORGANOPHOSPHORUS ESTERS IN STRUCTURE-REACTIVITY STUDIES

In order to study the polar substituent effect almost with no steric effect in organophosphorus chemistry,a series of 4-substituted-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane 1-oxides(1)and p-substituted phenylphosphonates(2)and corresponding mono hexyl esters(3)as model were synthesized.^(31)P-NMR chemical shifts of compounds(1)in methanol and deuterioacetone were determined.The Δδ values reflect 4-sbstituent po- lar effect.The ^(31)P-NMR of compounds(2)and(3)and the pKa of compounds(3)were also measured.The results showed that the trend of polar effects of substituents in both carboxylic and organophosphates chemistry are similar,and the change of polar effects in variation with the alkyl groups is not significant.

Substituent Effect on Mercury-199 Chemical Shifts in Some Bisarylmercurials and Aryl(2-benzothiazolylthio) mercurials

The present paper covers the 199 Hg NMR chemical shifts of 24 substituted diphenylmercurials and phenyl(2-benzothiazolylthio)mercurials. There is a good linear relationship between the chemical shift and the Hammett constant of the substituents for both series of compounds, and electron donating substituents cause the chemical shift towards downfield.

Effects of Pressure, Solvent, and Substituent on the Thermal Isomerization of 2-Oxo- spiro[diazirine-3,3'-indoline]

The kinetic effects of pressure, solvent, and substituent on the thermal isomerization from 2 oxospiro[diazirine 3,3 indoline] to 3 diazo 2 oxo indoline have been examined. The rate constants of the thermal isomerization increased with increasing external pressure and were related to the σ + P substituent constant of Hammett correlation. The results suggest that the thermal isomerization proceeds via a dipolar transition state involving heterolytic bond fission. However, the kinetic solvent effects on the thermal isomerization were not observed. The special solvent effects were discussed on the basis of the linear free energy relationship.

Theoretical Studies on Substituent Effect of the Reaction of Amide and Formaldehyde

The thermodynamic properties of the reaction of amide and formaldehyde were calculated via B3LYP method when substituents chosen included CH3,CH2CH3,CH2CH2CH3,CH2CH2CH2CH3,CH（CH3）2,CH2CH（CH3）2,CH（CH3）CH2CH3 and C（CH3）3.Based on the optimization of the structures for reactants and products,the thermodynamic functions of all the species for an actual state were obtained.The thermodynamic data and the equilibrium constants were investigated within a temperature range of 300―343.15 K.The calculated results show that the reaction is exothermic and spontaneous.The trends of all thermodynamic properties are consistent with the temperature.The preferential order of the substituent effect is CH2CH（CH3）2CH（CH3）CH2CH3CH2CH2CH2CH3 CH2CH2CH3CH2CH3≈CH（CH3）2C（CH3）3≈CH3.

Theoretical Study of Impact of Side Substituent Effecton Intramolecular Proton Transfer of Perylenequinone

Semi-empirical molecular orbital theory AMI method is employed to study the ortho-position substituent impact on intramolecular proton transfer reaction of perylenequinone. The calculation demonstrates that the perylenequinone molecule is of stable structure. and all substituents may cause the decrease of barriers for the hydrogen transfer reaction.

Substituent Effects on the Hydrogen Bonding Between Phenolate and HF, H_2O and NH_3

B3LYP/6 31+g( d ) calculations were performed on the hydrogen bonded complexes between substituted phenolates and HF, H 2O as well as NH 3. It was found that some properties of the non covalent complexes, including the interaction energies, donor acceptor (host guest) distances, bond lengths, and vibration frequencies, could show well defined substituent effects. Thus, from the substituent studies we can not only understand the mechanism of a particular non covalent interaction better, but also easily predict the interaction energies and structures of a particular non covalent complex, which might otherwise be very hard or resource consuming to be known. This means that substituent effect is indeed a useful tool to be used in supramolecular chemistry and therefore, many valuable studies remain to be carried out.

SYNTHESES AND SUBSTITUENT EFFECTS ON 4-^(13)C-NMR OF BIOACTIVE 4-SUBSTITUTED-2,6,7-TRIOXA-1-PHOSPHABICYCLO[2.2.2]OCTANE-1-OXIDES

Ten 4-substituted bicyclic phosphates were synthesized and their ^(13)C-NMR were also determined.A good relationship was observed between 4-^(13)C chemical shift and Taft σ_X induc- tive paramenters.Substituent effects on ~3J_(P-C) coupling constant were studied.

“Substituents optimization”and“push effect”dual strategy for design of cobalt phthalocyanine catalyst on oxygen reduction reaction

Molecular metallocycle electrocatalysts like metalloporphyrins and metallophthalocyanines were found to be effective for oxygen reduction reaction(ORR)due to their M-N_(4) active sites and large conjugated elec-tronic molecular structures.Herein,the“substituents optimization”strategy combined with“push effect”modification was innovatively employed to target a single Co-N_(4) active site in three substituted phthalo-cyaninato cobalt complexes:tetranitrophthalocyaninato cobalt(CoTNPc),tetra(4-nitrophenoxy)phthalo-cyaninato cobalt(CoTPNPc),and tetraphenoxy phthalocyaninato cobalt(CoTPPc)electrocatalyst,also with 4-phenylpyridine axial coordination on Co-N_(4) unit.Through substituents screening,the half-wave poten-tial(E_(1/2))for ORR increases in the order of CoTPNPc(0.75 V)<CoTPPc(0.80 V)<CoTNPc(0.83 V)along with decreased electron-withdrawing ability of their substituents from-OC_(6) H_(4)-NO_(2),-OC_(6) H_(5) to-NO_(2) in the three cobalt phthalocyanine derivatives.CoTNPc with the weakest electron-withdrawing substituent exhibits the best ORR performance among the three compounds.This is attributed to its higher elec-tron delocalization and lifted HOMO energy level with the lower energy barrier in the rate-determining step relative to the other two compounds,which facilitate the electron transfer and reduction of oxy-gen as evidenced by XPS,UPS,and DRS analysis combined with DFT calculations.Further coordination of 4-phenylpyridine shifts the E_(1/2) up to 0.78,0.82,and 0.85 V for CoTPNPc,CoTPPc,and CoTNPc.DFT calcu-lations demonstrate that the introduction of the electron-donating phenylpyridine ligand into the cobalt phthalocyanines breaks the symmetry of the Co-N_(4) center and also raises the electron density of Co sites,which promotes O_(2) adsorption and improves ORR performance.After comparing the two strategies,the substituents on metallophthalocyanine are more determined by the electroactivity than the axial group,which directly regulates the coordination environment and then the activation barrier of the ORR pro-cess.This work provides theoretical and experimental guidance by two coupling strategies for the design of highly active molecular CoPc-based ORR electrocatalysts in the practical application.

Identification of a Reliable DFT Calculation Method to Predict the Ground-and Excited-State Properties of Nickel(Ⅱ) Complexes with Porphyrin in Crude Oil

Metalloporphyrins have devastating effects on the deep processing and efficient utilization of petroleum resources. Various porphyrins are derived from porphin by substitution at the β, meso, or both positions. Herein, we focus on the interaction between nickel(Ⅱ) and the porphyrin skeleton. Five different density functionals were selected for determining a reliable approach to simulate porphyrin-nickel(Ⅱ) complexes. At D4h symmetry, the 10b1g, 15a1g, 4e1g and 9b2g were dominated by the 3d character of nickel. Compared with pure density functional, the hybrid functional gave larger highest occupied molecular orbital(HOMO) and lowest unoccupied molecular orbital(LUMO) gap, and the higher HOMO-LUMO gap also corresponded to a higher excitation energy. The characteristic Soret and Q bands modeled by timedependent density functional theory(TDDFT) calculations matched well with experimental results, and the absorption was discussed in detail with natural transition orbitals(NTO) analysis. Furthermore, the binding character of nickel(Ⅱ) with various substituted porphyrins were calculated at perdew-burke-ernzerhof(PBE) level, showed that the geometry and complexation behavior of porphyrin-nickel(Ⅱ) complexes could be significantly tuned by different substituents. The symmetry of the complex was reduced and the skeleton ring get distortion when introducing different substituents. Compared with ETIO porphyrin, the introduction of phenyl on the β position can expand the conjugated system and promote the covalent character of Ni-N bond.

Effect of substituents in hydroxyl radical-mediated degradation of azo pyridone dyes: Theoretical approaches on the reaction mechanism

Understanding the degradation behavior of azo dyes in photocatalytic wastewater treatment is of fundamental and practical importance for their application in textile-processing and other coloration industries. In this study, quantum chemistry, as density functional theory, was used to elucidate different degradation pathways of azo pyridone dyes in a hydroxyl radical(HO ·)-initiated photocatalytic system. A series of substituted azo pyridone dyes were synthesized by changing the substituent group in the para position of the benzene moiety, ranging from strong electron-donating to strong electron-withdrawing groups. The effect of dye molecular structure on the photocatalytic degradation reaction mechanism was analyzed and quantification of substituent effects on the thermodynamic and kinetics parameters was performed. Potential energy surface analysis revealed the most susceptible reaction site for the HO ·attack. The calculated reaction barriers are found to be strongly affected by the nature of substituent group with a good correlation using Hammett σp constants and experimentally determined reaction rates. The stability of pre-reaction complexes and transition state complexes were analyzed applying the distortion-interaction model. The increased stability of the transition state complexes with the distancing from the substituent group has been established.

Theoretical Study of the N-NO_2 Bond Dissociation Energies for Energetic Materials with Density Functional Theory

The N-NO2 bond dissociation energies （BDEs） for 7 energetic materials were computed by means of accurate density functional theory （B3LYP, B3PW91 and B3P86） with 6-31G＊＊ and 6-311G＊＊ basis sets. By comparing the computed energies and experimental results, we find that the B3P86/6-311G＊＊ method can give good results of BDE, which has the mean absolute deviation of 1.30kcal/mol. In addition, substituent effects were also taken into account. It is noted that the Hammett constants of substituent groups are related to the BDEs of the N-NO2 bond and the bond dissociation energies of the energetic materials studied decrease when increasing the number of NO2 group.

Studies on the Properties of Schiff Base Type of Aryl mercury Compounds( Ⅰ )——~1H NMR Spectra of Some Schiff Base Type Aryl mercury Compounds and Substituted Benzyl ideneanilines

1H NMR spectra of 16 Schiff base type of arylmercury compounds and 4 -substituted benzylideneanilines have been studied. It was found that the p-substituents of the N-phenyl ring do not affect the δ values of methine proton, whereas the o-substitutents influence the δ values of methine proton, whereas the o-substituents influence the δ values of methine proton significantly. These changes can be reasonably interpreted in terms of the steric inhibition of o-substituents and intramolecular coordination of imino nitrogen with mercury. The influence of the m-or p-substituent of the C-phenyl ring on the δ values of methine proton exhibited a linear correlation with Hammett constants σp or σm. It was also confirmed that in the molecules of Schiff base type of arylmercury compounds there exists an intramolecular coordination via a four-membered ring.

A Quantum Chemical Investigation on the Antioxidant Activity of Licoisoflavone Derivatives

In this paper,21 substituents with various electron donating and electron withdrawing characters were placed in the available positions of Licoisoflavone in order to study their effect on the three O–H bond dissociation enthalpies and ionisation potential via DFT/B3LYP method.Results show that the B-ring is more important than the A-ring from the BDE and IP point of view because the radical structure formed after hydrogen atom abstraction from the 4-OH group can be stabilized by the resonance between the three rings.The results show that intramolecular hydrogen bonding effects are able to considerably stabilize the parents and radicals.The NBO analysis results also confirmed the intramolecular hydrogen bond stabilization.The formation of strong intramolecular hydrogen bonds and suitable spin density distributions in several radicals result in low BDE and IP values.The calculated BDE and IP values have been correlated with Hammett constants.The found dependencies are suitably linear,which can be important for the synthesis of novel antioxidants based on Licoisoflavone.

SYNTHESIS AND FREE RADICAL RING-OPENING POLYMERIZATION OF 2-METHYL-AND 2-METHYL-9-n-BUTYL-(-7-METHYLENE-1,4,6-TRIOXA-SPIRO (4, 4)NONANE)

This paper describes the synthesis and free radical ring-opening polymerization of 2-methyl-and 2-methyl-9-n-butyl (-7-methylene-1, 4, 6-trioxaspiro (4, 4) nonane). The structures of the two polymers were verified by IR, 'H and ^(13)C NMR spectra. The substituent on 9-position of 7-methylene-trioxaspiro (4, 4) nonane affects the structure of polymer and polymerization activity. The polymerization mechanism is discussed.

Antioxidant Activity of Substituted Enterolactone Derivatives in the Gas Phase and Water

The antioxidant activity of ortho and meta substituted Enterolactone derivatives has been investigated in the gas phase and water.The reaction enthalpies of antioxidant activity of the studied derivatives have been calculated and compared with the corresponding values of Enterolactone.Results show that EWG substituents increase the BDE and IP,while the EDG ones rise in the PA.The Enterolactone derivatives with the lowest BDE,IP and PA values were identified as the compounds with high antioxidant activity.Results show that the substituents in the ortho position have high potential for the synthesis of novel Enterolactone derivatives.Results show that Enterolactone derivatives can processes their protective role via HAT and SPLET mechanism in gas phase and solvent,respectively.The calculated reaction enthalpies of the substituted Enterolactones have linear dependence with Hammett constants and EHOMO that can be utilized in the selection of suitable substituents for the synthesis of novel antioxidants based on Enterolactone.

^(99)Ru and ^(13)C-NMR Spectra for the Tris Chelates of 5-Substituted 1,10-Phenanthrolines with Ruthenium (Ⅱ)

13C and 99Ru-NMR chendcal shifts are reported for the ruthenium(II) tris complexes of5-substitUted 1,10-phenanthrolines. It has been found that both of them are affected by the substituents on the phenanthrolines in a direction consistent with that expected from the electron withdrawing ability of the substituent.

A-DA’D-A Type Pentacyclic Small Molecule Acceptors to Exceed 16.5%Efficiency by Heteroatom Effect at the Outer Side Chain

Comprehensive Summary In this work,we adopt a“heteroatom side-chains”modification strategy to modify the thiophene units in A-DA'D-A(acceptor-donor-acceptor’-donor-acceptor)type pentacyclic SMAs(small molecule acceptors),that is,introducing branched alkyl chain at theβ-position of thiophene instead of straight alkyl chain,and then introducing oxygen atom at the third-position on the basis of branched chain.Two new pentacyclic SMAs(BZ4F-EH and BZ4F-OEH)were synthesized,and the influence of the heteroatom side-chains on photoelectric properties of A-DA'D-A type pentacyclic SMAs was systematically studied.Compared with our previously reported BZ4F(Y26),BZ4F-EH shows slightly blue-shifted absorption,while BZ4F-OEH has obvious red-shifted absorption.As a result,BZ4F-OEH-based binary device achieved a high power conversion efficiency(PCE)of 16.56%with a fill factor(FF)of 79.3%,which is the highest efficiency of pentacyclic SMAs to date.