Substituent Effects on 13C NMR and 1H NMR Chemical Shifts of CH=N in Multi-substituted Benzylideneanilines

Fifty-three samples of multi-substituted benzylideneanilines XArCH=NArYs （abbreviated XBAYs） were synthesized and their NMR spectra were determined. An extensional study of substituent effects on the 1H NMR chemical shifts （δH（CH=N）） and 13C NMR chemical shifts （δc（CH=N）） of the CH=N bridging group from di-substituted to multi-substituted XBAYs was made based on a total of 182 samples of XBAYs, together with the NMR data of other 129 samples of di-substituted XBAYs quoted from literatures. The results show thatthe substituent specific cross-interaction effect parameter （△（∑σ）2） plays an important role in quantifying the δc（CH=N） values of XBAYs, but it is negligible for quantifying the δH （CH=N） values; the other substituent parameters also present different influences on the δc （CH=N） and （δH （CH=N）. On the whole, the contributions of X and Y to the δc （CH=N） of XBAYs are balanced, but the δH（CH=N） values of XBAYs mainly rely on the contributions of X.

Substituent Effects on Reduction Potentials of Meta-substituted and Para-substituted Benzylideneanilines

Effects of meta-substituent of 3,4＇/4,3＇/3,3＇-substituted benzylideneanilines （XBAYs） on the electrochemical reduction potentials （E（Red）） were investigated, in which 49 samples of target compounds were synthesized, and their reduction potentials were measured by cyclic voltammetry. The substituent effects on the E（Red） of target compounds were analyzed and an optimality equation with four parameters （Hammett constant a of X, Hammett constant a of Y, excited-state substituent constant σexCC of X, and the substituent specific cross-interaction effect △σexCC2 between X and Y） was obtained. The results show that the factors affecting the E（Red） of 3,4＇/4,31/3,3P-substituted XBAYs are different from those of 4,4＇-substituted XBAYs. For 3,4＇/4,3＇/3,3＇-substituted XBAYs, σ（X） and σ（Y） must be employed, and the contribution of △σexCC2 is important and not negligible. Compared with 4,4＇-substituted XBAYs, X group contributes less to 3,4＇/4,3＇/3,3＇-substituted XBAYs, while Y group contributes more to them. Additionally, it was observed that either para-substituted XBAYs or meta-substituted XBAYs, the substituent effects of X are larger than those of Y on the E（Red） of substituted XBAYs.

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.

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.

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.

A Distinctive Pattern for Substituent Effects on Transition Metal Centers:Enhanced Electron-Donating Capacity of Cationic Palladium Species

Electronic and bonding situations at reaction centers are often detected by the remote substituent effect.For nonorganometallic reactions,this effect is conventionally described by the well-known Hammett-type substituent constants.However,for most transition metal(TM)-involved systems,no analogous numeral descriptors reflecting the intrinsic differences between metallic and nonmetallic bonding have been rigorously established till present.Herein,we report a Pd(II)–O bond heterolysis energyΔG_(het)(Pd–O)study of the archetypal palladium complexes to represent the thermodynamics of the essential bond-breaking step in Pd-mediated transformations.Meanwhile we furnish the new substituent constantsσPd^(+)s and therefrom facilitate linear free-energy relationship(LFER)analysis for Pd-catalyzed reactions.Indeed,this led us to find an unexpected electron-donating ability of Pd(II)cation,which provided a gifted experimental support,with the aid of computation,to attribute the frustrating observation of a much scattered curvature in theΔG_(het)(Pd–O)-σ+correlation to the electrondonating capacity of the cationic palladium through back-donation of its d-electrons.Applications of LFER analysis withσPd^(+)to predict the redox behavior of the palladium complex and in a kinetics vs.thermodynamicsmechanistic study of transmetalation added further credence to their applicability to TM systems.

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.

Substituent Effects on Direct Arylation Polycondensation and Optical Properties of Alternating Fluorene-Thiophene Copolymers

Four thiophene derivatives were prepared by replacing the 3,4 positions of thiophene by―OCH3, ―CH3―COOCH3 and ―CN, respectively. The polycondensations via direct arylation took place between the four thiophene derivatives and 2,7-dibromo-9,9-dioctylfluorene under six various catalytic conditions to investigate the substituent effects. The substituent can affect the electron cloud density of the active C―H bond, which can be monitored by the NMR chemical shift. The experimental results show that the reactivity decreases with increasing the chemical shift of active C―H bonds in the four thiophene derivatives, and thus can promote the direct arylation polycondensation. This phenomenon is explained by the electrophilic aromatic substitution（SEAr） mechanism. UV-Visible absorption and photoluminescence were studied to investigate the substituent effect on optical properties of the four copolymers. The results show that these alternating fluorene-thiophene copolymers with different substituents are good fluorescent materials and promising in PLED applications.

Aldol Condensation and Michael Addition of 4,4-Dimethyl- cyclohexane-l,3-dione and Aromatic Aldehydes, Unconventional Substituent Effects

By the cyclization of 4,4-dimethylcyclohexane-1,3-dione with different aromatic aldehydes, the xanthene regio- isomers were obtained. The diversity of xanthene isomers could be determined. The electronic and steric effects on aromatic aldehydes could be observed.

Recent progress in quantifying substituent effects

This paper summarizes significant progress in quantifying organic substituent effects in the last 20 years. The main content is as follows： （1） The principle of electronegativity equalization has gained wide acceptance, and has been used to calculate the intramolecular charge distribution and inductive effect of groups. A valence electrons equalization method was proposed to compute the molecular electronegativity on the basis of geometric mean method, harmonic mean method, and weighted mean method. This new calculation method further extended the application of the principle of electronegativity equalization. （2） A scale method was established for experimentally determining the electrophilic and nucleophilic ability of reagents, in which benzhydryliumions and quinone methides were taken as the reference compounds, and the research field was extended to the gas phase conditions, organometallic reaction and radicals system. Moreover, the nucleophilicity parameters N and electro- philicity parameters E for a series of reagents were obtained. The definition and quantitative expression of electrophilicity in- dex co and nucleophilicity index co were proposed theoretically, and the correlation between the parameters from experimental determination and the indexes from theoretical calculation was also investigated. （3） The polarizability effect parameter was initially calculated by empirical method and further developed by quantum chemistry method. Recently, the polarizability ef- fect index of alkyl （PEI） and groups （PEIx） were proposed by statistical method, and got wide applications in explaining and estimating gas-phase acidity and basicity, ionization energy, enthalpy of formation, bond energy, reaction rate, water solubility and chromatographic retention for organic compounds. （4） The excited-state substituent constant Crcc obtained directly from the UV absorption energy data of substituted benzenes, is different from the polar constants in molecular ground state and the radical spin-delocalization effects constants in molecular radical state. The proposed constant Crcc correlated well with the UV absorption energy of many kinds of organic compounds, such as 1,4-disubstituted benzenes, substituted stilbenes, and di- substituted N-benzylidenebenzenamine. （5） The establishment of the steric shielding effect distinguished the three traditional steric effects. The stereoselectivity index Ci was proposed to quantify the stereoselectivity of the addition reaction of carbonyl with nucleophilic reagent. The shielding parameter Rs was defined to quantitatively express the specific surface of the reac- tion center screened by a group. Further, the Topological Steric Effect Index （TSEI） of a group was proposed on the basis of the relative specific volume of reaction center screened by the atoms of substituents. These parameters can be applied in esti- mating the intramolecular dihedral angles, stereoselectivity of reaction, enthalpies of formation of alkenes and alkylbenzene, acidity of substitutedimidazolium ionic liquid, and the reaction rate of alkane and hydroxyl radical. In addition, some sugges- tions and prospects for further studies on quantifying the organic substituent effects were presented in this paper.

Theoretical Study of Remote Substituent Effects on X-H （X=CH2, NH, O） Bond Dissociation Energies of Azulene

In the study, the X-H （X=CH2, NH, O） bond dissociation energies （BDE） of para-substituted azulene （Y-C10H8X-H） were predicted theoretically for the first time using Density Functronal Theory （DFT） methods at UB3LYP/6-311 ＋ ＋g（2df,2p）//UB3LYP/6-31 ＋g（d） level. It was found that the substituents exerted similar effects on the X-H BDE of azulene as those on benzene, except for 6-substituted 2-methylazulene. Owing to the substituent-dipole interaction, the reaction constants （ρ^＋） of 2- and 6-Y-CIoHsX-H （X=NH and O only） varied violently. The origin of the substituent effects on the X-H BDE of azulene was found, by both GE/RE and SIE theory, to be directly associated with variation of the radical effects, although the ground effects also played a modest role in determining the net. substituent effects.

Substituent effects on novel lanthanide(Ⅲ) hydrazides complexes

New lanthanide(Eu3+ and Gd3+) complexes were successfully synthesized and the effect of the p-phe nyl substituent on the Eu3+luminescent properties was evaluated.In this sense,benzhydrazide,p-toluic hydrazide,4-hydroxybenzhydrazide and 4-aminobenzoic hydrazide were used as ligands and the complexes were obtained by mixing the lanthanide salts with hydrazides in ethanol at room temperature and keeping the reaction for 2 h under mechanical stirring.Crystal of Gd-amino was obtained and its structure was elucidated by single-crystal X-ray diffraction,revealing that Gd3+centered in a distorted tricapped trigonal-prismatic molecular geometry.IR spectroscopy and the elucidated structure confirm hydrazides acting as bidentate ligands binding to Ln3+ions through the oxygen of carbonyl group and the nitrogen of terminal amine,forming a five-membered ring,CHN analyses confirm the molecular formulas [Gd(amino)4(H2 O)](NO3)3·(C2 H5 OH) and [Eu(toluic)3(H2 O)3](NO3)3.Lower T1 state energies are observed for ligands p-substituted with higher electron donating capacity groups,such as p-NH2 and pOH.In contrast,higher lifetimes and quantum efficiencies are obtained for Eu3+complexes with ligands p-H and p-CH3 substituted,which are not deactivator groups.

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.

Substituent Effects on the Blue-Shifting Hydrogen Bonds between X-C≡C-CF_2-H and Water

MP2/6-31 + g(d) calculations were performed verifying the existences ofblue-shifting X - C ≡ C - CF_2 - H···OH_2 hydrogen bonds. Detailed analyses revealed that theinteraction energy and donor-acceptor distance had good correlations with the substituent Hammettconstants. However, the extent of C―H bond contraction and the blue shift of the C―H stretchingvibration did not show any good correlation with the traditional substituent constants, indicatingthat certain more complicated mechanisms might be involved in the present systems. Nevertheless, itwas found that highly electron-withdrawing susbtituents were not favorable to the C―H bondcontraction, and it was suggested that the attractive interaction between water and the carbon of -CF_2H probably played an important role in the blue shift.

α-Substituent Effects on Si--H, P- H and S--H Bond Dissociation Energies

CBS-Q and G3 methods were used to generate a large number of reliable Si--H, P---H and S--H bond dissociation energies （BDEs） for the first time. It was found that the Si--H BDE displayed dramatically different substituent effects compared with the C--H BDE. On the other hand, the P---H and S--H BDE exhibited patterns of substituent effects similar to those of the N--H and O--H BDE. Further analysis indicated that increasing the positive charge on Si of XSiH3 would strengthen the Si--H bond whereas increasing the positive charge on P and S of XPH2 and XSH would weaken the P---H and S--H bonds. Meanwhile, increasing the positive charge on Si of XSiH2^＋ stabilized the silyl radical whereas increasing the positive charge on P and S in XPH＂ and XS＊ destabilized P- and S-centered radicals. These behaviors could be reasonalized by the fact that Si is less electronegative than H while P and S are not. Finally, it was demonstrated that the spin-delocalization effect was valid for the Si-, P- and S-centered radicals.

Substituent Effects on the Low-Frequency Vibrational Modes of Benzoic Acid and Related Compounds

Well-resolved absorption spectra of benzoic acid and its derivatives with one hydrogen atom replaced by a substituent group CH3, OH, NH2 or NO2 were reported in the frequency region between 6 and 67 cm^-1 at room temperature with terahertz time-domain spectroscopy （THz-TDS）. These substances can be distinguished easily based on the terahertz absorption spectra. The measurements suggested that even minor changes in the molecular configuration and chemical composition lead to distinct differences in THz spectrum. Density functional theory （DFT） method was used to assist the analysis and assignment of the individual THz absorption spectra of benzoic acid and its methyl derivatives. Observed THz responses of samples can be assigned to the collective vibrations associated with intermolecular hydrogen bonds.

Substituent Effects on the Hydrogen Bonding between 4-Substituted Phenols and HF,H_2O,NH_3

Density function theory UB3LYP/6-31+g(d) calculations were performed to study the hydrogen bonds between para -substituted phenols and HF,H_2O,or NH_3. It revealed that many properties of the non-covalent complexes,such as the interaction energies,donor-acceptor distances,bond lengths and vibration frequencies,showed well-defined substituent effects. Therefore,from the substituent effects not only the mechanism of a certain non-covalent interaction can be better understood,but also the interaction energies and structures of a certain non-covalent complex,which otherwise might be very hard or resource-consuming to estimate,can be easily predicted.

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.

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.