A correlation of substituent effects with proton chemical shifts in aromatic tetrazolic acids

The effect of substituents on the proton chemical shifts and spin–spin coupling constants in ortho-, meta- and para-substituted 5-phenyltetrazoles (tetrazolic acids) in DMSO–CH₃CN (1:1, v/v) was studied. With the meta- and para- substituted compounds the additivity rule of chemical shifts was obeyed, thereby enabling increments characterizing the effects of individual substituents in monosubstituted benzenes to be determined. By employing the Smith and Proulx equation, the chemical shifts of the aromatic protons were correlated with the F, R and Q substituent constants. The values of these constants are 1.02, ?0.004 and 5.49, respectively, for the tetrazolyl substituent.     

Substituent Effect on the C–NO2 and N–NO2 Bond Dissociation Energies of Nitroaromatic Molecules

Six density function theory methods (B3LYP, B3P86, MPWB1K1, MPWPW91, PBEPBE, TPSS1KCIS3) were used to calculate bond dissociation enthalpies of nitro compounds, where the B3P86 method was found to give the most accurate predictions. Using the B3P86 method meta‐ and para‐substituted nitroaromatics were systematically studied for the first time. The remote substituent effects, Hammett relationships, and the origin of the substituent effects were discussed on the basis of the calculated results. Both meta‐ and para‐substituted nitromethyl‐benzenes showed significant substituent effects and a fair correlation against substituent constants σ_p⁺ The ground state effects were found to play the major role in determining the overall substituent effects. Meanwhile, nitroamino‐ benzenes showed irregular substituent effects and a poorer Hammett correlation, where both ground and radical state effects contributed to the overall substituent effects.     

1-萘甲酰苯胺和2-萘甲酰苯胺的分子内电荷转移研究

A series of 1-naphthanilides (1) and 2-naphthanilides (2) with varied substituents at the para- or meta-position of anilino phenyl ring were prepared and their absorption and fluorescence spectra in a nonpolar solvent cyclohexane were investigated. An abnormal long wavelength emission assigned to the charge transfer (CT) state was found for all of the prepared naphthanilides in cyclohexane. A linear free energy correlation between the CT emission energies and the Hammett constants of the substituent was found within series 1 and 2. The value of the linear slope with 1 (0.42 eV) was higher than that with 2 (0.32 eV) being close to that of the substituted benzanilides 3 (0.31 eV) The higher slope value suggested higher charge separation extent in the CT state of 1 than that of 2. It was found that the corresponding linear slope of anilino-substituted benzanilides remained unchanged when para-, meta-, ortho-, or ortho, ortho-methyls were introduced into the anilino moiety, which ruled out the possible contribution of the difference in the steric effect and the electron accepting ability of the naphthoyl acceptor in 1 and 2. Compared with the early reported N-substituted-benzoyl-aminonaphthalene derivatives 4 and 5, it was considered that 1-naphthoyl enhanced the charge transfer in 1 and the proximity of its ^1La and ^1Lb states was suggested to be responsible. It was shown that 1- and/or 2-substituted naphthalene cores acting as either electron acceptor (naphthoyl) or electron donor (aminonaphthalene) were different in not only electron accepting (donating) ability but also shaping the charge transfer pathway.     

Carbon-13 NMR studies on some 5-substituted quinoxalines

Eleven 5-substituted quinoxalines (NO₂, NH₂, COOH, OCH₃, CH₃, OH, F, Cl, Br, I, CN, the latter five not reported previously) have been synthesized by standard methods. Their ¹³C NMR spectra have been measured in DMSO-d₆ and assigned on the basis of substituent parameters, by line widths and by intensities. The chemical shifts compare favorably with those calculated using benzene substituent parameters, and are very close to those of corresponding carbons in 1-substituted phenazines. The correlation with the chemical shifts of the corresponding positions in 1-substituted naphthalenes is also close except for those of carbons 4a and 8a in the quinoxalines which, due to their proximity to nitrogen, are downfield (in some cases 12 ppm) of the signals of the corresponding carbons in naphthalene. 5-Fluoroquinoxaline was also measured in CDCl₃, CD₃COCD₃, CD₃CN, CD₃OD, C₆D₆ and CD₃COOD. In all solvents an abnormally low ²J(CF) (～ 12 Hz) was found for C-4a and no C? F spin-spin splitting could be detected for the three-bond coupling of C-8a. Similar abnormalities were found in 2-fluoroaniline and 2-fluoroacetanilide. There are linear relationships between the Q parameter of the substituent and the chemical shift of carbons 4a, 5 and 6. A linear relationship also exists between the chemical shift of C-8 (‘para’ position) and the Hammett σ_p parameter of the substituent.     

Carbon-13 NMR study of substituted benzyl N,N-dimethylcarbamates

The ¹³C NMR chemical shifts of m- and p-substituted benzyl N,N-dimethylcarbamates were measured in CDCl₃. The meta and para ¹³C substituent chemical shifts were analysed by means of dual substituent parameter (DSP) equations. Good correlations were obtained, especially for the para-carbon substituent chemical shifts. The computed transmission coefficients, ρ_I and ρ_R, are consistent with the general features of the fitting parameters. It has been shown that no significant electron demand is imposed by the ? CH₂OCON(CH₃)₂ substituent.     

Substituent and solvent effects on the 19F chemical shifts of 3- and 4-XCH2-substituted fluorobenzenes

Substituent effects on the ¹⁹F chemical shifts of a series of 3- and 4-XCH₂-substituted fluorobenzenes have been studied in five different solvents (dimethyl sulphoxide, acetone, chloroform, carbon tetrachloride and benzene). The results show that in both series substituent effects (other than inductive effects) contribute in at least some cases to the overall shifts, but that these showed little solvent dependence. The meta series showed a proportionately greater solvent dependence than the para series, and this is attributed to the greater importance of ‘through solvent’ direct field effects in the former.     

A stress tensor and QTAIM perspective on the substituent effects of biphenyl subjected to torsion

The Quantum Theory of Atoms in Molecules (QTAIM) defines quantities in 3D space that can be easily obtained from routine quantum chemical calculations. The present investigation shows that local properties can be related quantitatively to measures traditionally connected to experimental data, such as Hammett constants. We consider the specific case of substituted biphenyl to quantify the effects of a torsion φ, 0.0° ≤ φ ≤ 180.0°, of the C—C bond linking the two phenyl rings for C₁₂H₉‐x, where x = N(CH₃)₂, NH₂, CH₃, CHO, CN, NO_2, on the entire molecule. QTAIM interpreted Hammett constants, aΔH( r_b ) are introduced and constructed using the difference between the H( r_b ) value of C₁₂H₉‐x and the C₁₂H₉‐H, biphenyl which is the reference molecule, with a constant of proportionality a. This investigation unexpectedly yields very good or good agreement for the x groups with the Hammett para‐, meta‐, and ortho‐substituent constants and is checked against para‐substituted benzene. We then proceed to present the interpreted substituent constants of seven new biphenyl substituent groups, where tabulated Hammett substituent constant values are not available; y = SiH₃, ZnCl, COOCH₃, SO₂NH₂, SO₂OH, COCl, CB₃. Consistency is found for the QTAIM interpreted biphenyl substituent constants of the seven new groups y independently using the stress tensor polarizability P_σ. In addition, a selection of future applications is discussed that highlight the usefulness of this approach. © 2016 Wiley Periodicals, Inc.     

The effect of solvent accessible surface on Hammett‐type dependencies of infinite dilution 29Si and 13C NMR shifts in ring substituted silylated phenols dissolved in chloroform and acetone

Infinite dilution ²⁹Si and ¹³C NMR chemical shifts were determined from concentration dependencies of the shifts in dilute chloroform and acetone solutions of para substituted O‐silylated phenols, 4‐R‐C₆H₄‐O‐SiR′₂R″ (R = Me, MeO, H, F, Cl, NMe₂, NH₂, and CF₃), where the silyl part included groups of different sizes: dimethylsilyl (R′ = Me, R″ = H), trimethylsilyl (R′ = R″ = Me), tert‐butyldimethylsilyl (R′ = Me, R″ = CMe₃), and tert‐butyldiphenylsilyl (R′ = C₆H₅, R″ = CMe₃). Dependencies of silicon and C‐1 carbon chemical shifts on Hammett substituent constants are discussed. It is shown that the substituent sensitivity of these chemical shifts is reduced by association with chloroform, the reduction being proportional to the solvent accessible surface of the oxygen atom in the Si‐O‐C link. Copyright © 2012 John Wiley & Sons, Ltd.     

17O NMR studies of ortho‐substituent effects in substituted phenyl tosylates

¹⁷O NMR spectra for 35 ortho‐, para‐, and meta‐substituted phenyl tosylates (phenyl 4‐methylbenzenesulfonates), 4‐CH₃‐C₆H₄SO₂OC₆H₄‐X, at natural abundance in acetonitrile at 50 °C were recorded. The ¹⁷O NMR chemical shifts, δ(¹⁷O), of the sulfonyl (SO₂) and the single‐bonded phenoxy (OPh) oxygens for para and meta derivatives correlated well with dual substituent parameter treatment using the Taft inductive, σ_I, and resonance, σº_R, constants. The influence of ortho substituents on the sulfonyl oxygen and the single‐bonded phenoxy oxygen chemical shifts, δ(¹⁷O), was found to be nicely described by the Charton equation: δ(¹⁷O)_ortho = δ(¹⁷O)_H + ρ_Iσ_I + ρ_Rσ°_R + δE_s^B when the data treatment was performed separately for electron‐donating +R substituents and electron‐attracting ?R substituents. Electron‐attracting meta and para substituents in the phenyl moiety caused deshielding while the electron‐donating meta, para and ortho +R substituents produce shielding effects on the sulfonyl (SO₂) and single‐bonded phenoxy (OPh) oxygens. The influence of ortho inductive and resonance effects in the case of +R substituents was found to be approximately twice higher than the corresponding influence from the para position. Due to the steric effect of ortho substituents a decrease in shielding of the oxygens at the sulfonyl group (δE_s^B > 0, E_s^B < 0) was detected. Copyright © 2012 John Wiley & Sons, Ltd.     

Proton and boron-11 magnetic resonance studies of some potassium tetraarylborates

Proton and boron-11 magnetic resonance spectra for several potassium para-substituted tetraarylborate compounds [KB(C₆H₄-pX)₄, where X is H, OCH₃, CH₃, Br, Cl, F, CF₃] have been obtained. The chemical shift between the centers of the AA′ and XX′ multiplets for the ring proton multiplets, relative to a reference chemical shift of 0·39 ppm for potassium tetraphenylborate, correlated with the corresponding Hammett σ values for the para-substituent. Additionally, the boron-11 chemical shifts gave a good correlation with corresponding σ values for the substituents. Electronegativities of para-substituted phenyl rings were calculated and found to be approximately 2·70 for all compounds studied. It was shown that electronic substituent effects do not greatly influence the electron density surrounding the central boron atom in the tetraarylborate ions.     

Studies on the kinetics of imidazolium fluorochromate oxidation of some meta‐ and para‐substituted anilines in nonaqueous media

The imidazolium fluorochromate (IFC) oxidation of meta‐ and para‐substituted anilines, in seven organic solvents, in the presence of p‐toluenesulfonic acid (TsOH) is first order in IFC and TsOH and is zero order with respect to substrate. The IFC oxidation of 15 meta‐ and para‐substituted anilines at 299–322 K complies with the isokinetic relationship but not to any of the linear free energy relationships; the isokinetic temperature lies within the experimental range. The specific rate of oxidizing species‐anilines reaction (k₂) correlates with substituent constants affording negative reaction constants. The rate data failed to correlate with macroscopic solvent parameters such as ε_r and E^N_T. A correlation of rate data with Kamlet–Taft solvatochromic parameters (α, β, π*) suggests that the specific solute–solvent interactions play a major role in governing the reactivity, and the observed solvent effects have been explained on the basis of solute–solvent complexation. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 166–175, 2006     

The Substituent Effect of 1‐Arylazonaphthen‐2‐ols on Azo‐hydrazone Tautomerization According to NMR Analysis

The substituent effect on azo‐hydrazone tautomerization of 1‐arylazonaphthen‐ols is studied by means of NMR analysis. Among the ¹³C chemical shifts, the C(2) of this series compound is the most sensitive to the variation in the nature of substituent on the phenyl ring. Therefore, the variation in the chemical shifts of C(2) is used to probe the substituent effect by using the substituent chemical shifts and free energy vs. Hammett’s constant (χρ⁺). Both methods give a negative correlation slope, indicating the electron‐with‐ drawing groups favor the hydrazone tautomer form. The effect on the chemical shifts of C(2) of compound 8 in ten solvents can be classified as the solvent with a proton‐donor, proton‐acceptor and arenes system. The substituent with electron‐donating character is more sensitive to the nature of solvent and it favors the hydrazone form. Free energy obtained from the dynamic NMR technique indicates the tautomerization favors the hydrazone‐form for the substituent with electron‐withdrawing character.     

Solvent and substituent effects on the electrochemical oxidation of substituted benzylamines in 2‐methylpropan‐2‐ol/water medium

Electrochemical oxidation of various para‐ and meta‐substituted benzylamines in different mole fractions of 2‐methylpropan‐2‐ol in water has been investigated in the presence of 0.1 M sulfuric acid as supporting electrolyte. The oxidation potential data of benzylamines correlates well with Hammett's substituent constants affording negative reaction constants (?1.112 < ρ > ?1.529). The correlation of the oxidation potential values with macroscopic solvent parameters is nonlinear, suggesting the operation of both specific and nonspecific solvent–solvent–solute interaction mechanisms. Correlation of the experimental data with Kamlet–Taft solvatochromic parameters is excellent (100r² > 98%) and the results reveal that the reactivity is influenced by the preferential solvational effects. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 371–377, 2007     

Carbon‐13 NMR and PM3 Study on the Substituent Effect of 1‐Aryl‐3,3‐Difluoro‐2‐Halocyclopropenes

The substituent‐induced chemical shifts (SCS) of C2 and C3 on the ¹³C NMR spectra of 1‐aryl‐3,3‐difluoro‐2‐halocyclopropenes were studied. The correlation between SCS and Hammett constants shows that the tendency of effect by the substituents on the phenyl ring is BrC2(ρ = 4.66) > ClC2(ρ = 4.50) and ClC3(ρ = ?1.63) > BrC3(ρ = ?1.41). The DSP treatment further confirms the SCS of C2 and C3 are the main contribution of the resonance effect and field effect, respectively. Those results of the incremental shifts reveals that the gem‐difluorocyclopropenyl bearing the phenyl group possesses a triple bond character, which is also observed in IR spectra with high n?_C=C (1768–1945 cm^?1).     

Towards physical interpretation of Hammett constants: charge transferred between active regions of substituents and a functional group

The charges transferred between substituents and two functional groups: nitroso and N,N-dimethylamine in disubstituted benzene rings, were calculated at the B3LYP/cc-pVDZ level, using Natural Population Analysis. They were compared with the charges transferred between active regions of the substituents and of the groups. The transferred charge was well correlated with the Hammett constants, but only when the charges were calculated for the corresponding active regions instead of being calculated for the substituents and functional groups themselves. The results were compared for substituents introduced at the para and meta position to the NO and N(CH₃)₂ groups.     

Investigation of substituent effects on the 1H NMR spectra of chalcones

¹H NMR spectra of 26 substituted chalcones (3-aryl-1 phenyl-2-propene-1-ones and 1-aryl-3-phenyl-2-propene-1-ones) have been studied. The chemical shifts of the α and β protons to the carbonyl group were correlated with Hammett s? parameters. To gain information on the effect of the transmission of the resonance and inductive contributions of the substituents on the chemical shifts of H-α and H-β, two parameter correlations with ?? and ?? parameters were also perfomed. The chemical shifts of the aromatic protons of the para-disubstituted benzene ring correlated with the a_i substituent increments.     

The NMR spectral characteristics of some meso-Ionic s-triazoles

The hetero-ring proton of anhydro-1,4-diphenyl-3-mercapto-s-triazolium hydroxide (I) is more highly deshielded than its 3-hydroxy analog (II). The chemical shifts of the hetero-ring proton for compounds I and II were found to be solvent dependent due to hydrogen bond formation. Two series of anhydro-1,4-diaryl-3-hydroxy-s-triazolium hydroxides have been synthesized and their NMR spectra determined. The chemical shift of the hetero-ring proton of these compounds was found to correlate with the Hammett sigma constants of the meta- and para- substituents in the aryl groups.     

Solvent effect on NMR spectra of poly(methyl methacrylate)

The NMR spectra of stereoblock poly(methyl methacrylate) in several solvents were measured. It is concluded from the following experimental results that the solute–solvent complexes are formed in benzene solution: the chemical shifts measured in C₆H₆ go to a lower field than do those in CDCl₃, except those of the ester methyl group, which splits into three resonances, and the shifts in the aromatic solvents are so different from those in the aliphatic solvents that Buckingham's theory cannot be applied to the results. The analysis of the temperature dependence of the chemical shifts of PMMA in benzene solution gave the heat of formation of the complex: ΔH = 2.8 ± 0.5 kcal./mole.     

On the Tacticity of Polynorbornenes with 5,6‐endo Pendant Groups That Contain Substituted Aryl Chromophores

Two dimers and a series of polymers with 5,6‐endo pendant aryl groups that contain different substituents at the para positions were synthesized. The conformation and stereochemistry of the dimers and polymers were determined by nonlinear optical analysis (EFISH) as well as UV/Vis and ¹³C NMR spectroscopy. The chemical shifts of C7 for the polymers appeared as two peaks in the ¹³C NMR spectra when the substituents are electron‐withdrawing groups. The percentage decrease in the relative extinction coefficient of the polymers, ε_d, was linearly related to the Hammett constant σ. Polynorbornenes with electron‐withdrawing substituents may adopt isotactic stereochemistry with all pendant groups aligned in one direction. The nature of the interactions between neighboring chromophores may be one of the most important factors in directing the stereoregularity and conformation of these polymers. The corresponding polymers derived from the exo isomers appeared to be less stereoregular.     

The effect of the structure of substituted phenylphosphonic difluorides on their 19F and 31P NMR spectral parameters

The ¹⁹F and ³¹P NMR spectral parameters of a series of meta and para substituted phenylphosphonic difluorides were found to be linearly related to the substituent parameters: the phosphorus chemical shifts correlated with Hammett's σ constant, the fluorine chemical shifts with Taft's σ_R parameter and the phosphorus–fluorine coupling constants with σ⁺.