Dual Parameter Equation Research Articles

Solubility of Xylene Isomers in Seven Deep Eutectic Solvents

Emissions of volatile organic compounds (VOCs) have a substantial impact on the environment, and absorption methods are an important means of dealing with VOCs. In order to screen potential deep eutectic solvents (DESs) as liquid absorbers for capturing xylenes, seven DESs were prepared and were verified by Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. The melting points of all DESs were well below the melting points of their raw materials, and the water content of all the DESs was less than 0.05 wt %. The viscosities of the seven DESs decreased with increasing temperature. The solubility of o-, m-, and p-xylene in the DESs was determined by the cloud point in the range of 303.15–353.15 K. The tetrabutylammonium bromide-based DESs had the greatest potential to dissolve xylene. Tetrabutylammonium bromide:triethylene glycol (1:4) exhibited the highest solubility for o-, m-, and p-xylene, with the mole fraction solubilities of 0.4075, 0.3754, and 0.3820, respectively (each at 353.15 K). The solubility magnitudes of the three isomers exhibited an overall trend of o-xylene > p-xylene ∼ m-xylene. The experimental solubility data were fitted with the dual-parameter equation and the Apelblat equation; the latter was a better fit.

Measurement and Correlation of the Solubility of Theobromine and Theophylline in Seven Imidazolium-Based Ionic Liquids at Various Temperatures

The solubility of theobromine and theophylline in seven pure imidazolium-based ionic liquids, including 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim]BF4), 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim]PF6), 1-butyl-3-methylimidazolium nitrate ([C4mim]NO3), 1-hexyl-3-methylimidazolium tetrafluoroborate ([C6mim]BF4), 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6mim]PF6), 1-hexyl-3-methylimidazolium nitrate ([C6mim]NO3), and 1-octyl-3-methylimidazolium tetrafluoroborate ([C8mim]BF4), were measured via a static method combined with high-performance liquid chromatography between T = 303.15–353.15 K at atmospheric pressure. The solubility of theobromine and theophylline in the selected ionic liquids increased as the temperature increased. Both cations and anions in the ionic liquids affected the solubility, but anions had a more pronounced effect than the cations with a trend of NO3– > BF4– > PF6–. The simplified dual-parameter equation, the Apelblat empirical equation, and the λh equa...

Determination and Correlation of the Solubility for Berberine Chloride in Pure Imidazolium-Based Ionic Liquids

The solubility of berberine chloride in several imidazolium-based ionic liquids (ILs), that is, [Rmim]BF4, [Rmim]NO3, [Rmim]PF6, and [Rmim]NTf2 (R = butyl, hexyl, and octyl), were measured using a laser monitoring observation method from 299.45 to 364.35 K at atmospheric pressure. The solubility of berberine chloride in selected ionic liquids increased as the temperature increased and is dominantly dependent on the type of IL’s anion structure with the trend of NTf2– ≫ NO3– > PF6– > BF4–. The ILs with NTf2– anion exhibited good dissolubility to berberine chloride, especially at high temperature. The correlated solubility data via Apelblat equation is in better agreement with the experiment solubility compared to Dual parameter equation and λh equation.

The substituent effect on the UV energy of 4,4′‐disubstituted benzylideneanilines

In this paper, 72 samples of disubstituted benzylideneanilines were all synthesized, and their UV data were measured in anhydrous ethanol. In the study on the UV energy of the titled compounds with single substituent changed, for the effect of the aniline substituent Y on the UV wavenumbers, its UV data can be correlated with a dual‐parameter equation; for the effect of benzylidene substituent X on the UV data, its UV energy can be correlated with a single‐parameter equation (Y is an electron‐withdrawing group and H) or a dual‐parameter equation (Y is an electron‐donating group). In the study on the UV energy of model compounds with double substituents changed, a correlation equation between the UV absorption wavenumbers and substituent constants and σp, was obtained. For 72 samples of 4,4′‐disubstituted benzylideneanilines, the correlation coefficient was 0.9876, and the standard deviation s was only 358.46 cm–1. The equation can be used to predict well the UV energy of BA derivatives. It was found that Δσ2 is a better parameter than σXY to scale the substituent cross‐interaction effect on the UV wavenumbers of benzylideneanilines molecules. The results implied that the law of substituent effect on the UV energy of titled compounds is different from that of substituted stilbenes, and it is helpful to understand the effect of substituent effects on the chemical and physical properties of conjugated compounds with an imine bridging group (C = N) or a nonplanar parent. Copyright © 2011 John Wiley & Sons, Ltd.

Electronic effects of heterocyclic ring systems as evaluated with the aid of 13C and 15N NMR chemical shifts and NBO analysis

AbstractThe electronic effects of the 5‐ and 6‐membered heterocyclic rings on the CNN unit of five different hydrazone derivatives of pyridine‐2‐, ‐3‐ and ‐4‐carbaldehydes, pyrrole‐2‐carbaldehyde, furan‐2‐ and ‐3‐carbaldehydes and thiophene‐2‐ and ‐3‐carbaldehydes have been studied with the aid of 13C and 15N NMR measurements together with the natural bond orbital (NBO) analysis. As model compounds are used the corresponding substituted benzaldehyde derivatives. The polarization of the CN unit of the hydrazone functionality of the heteroaryl derivatives occurs in an analogous manner with that of phenyl derivatives. The electron‐withdrawing heteroaryl groups destabilize and the electron‐donating groups stabilize the positive charge development at the CN carbon while the effect on the negative charge development is opposite. The 15N NMR chemical shift of the CN and CNN nitrogens and the NBO charges at CNN unit can be correlated with the replacement substituent constants σ of the heteroaryl groups. 13C NMR shifts of the CN carbon of N,N‐dialkylhydrazones of the heteroarenecarbaldehydes can be correlated with a dual parameter equation possessing the polar substituent constant σ* of the heteroaryl group and the electronegativity of the heteroatom as variables. Copyright © 2008 John Wiley & Sons, Ltd.

Ab Initio Calculations of Thermodynamic Hydricities of Transition-Metal Hydrides in Acetonitrile

Theoretical hydricities calculated by different methods are compared with all the available experimental values for the Co- and Ni-group metal hydrides in acetonitrile. It is found that the B3P86 method employing a sufficiently flexible basis set in combination with the C-PCM solvent model can accurately predict the hydricity with a precision of 2.0 kcal/mol. The same method can also accurately predict the acidities of the metal−hydrogen bond and the redox potentials of the corresponding metal hydrides with precisions of 1.9 pKa units and 0.07 V, respectively. On the other hand, an ONIOM method where the core layer is treated with the CCSD(T) method fails to predict the hydricity of transition-metal hydrides, possibly because the electronic effects of the outer layer are not accurately estimated with the low-level theory in the ONIOM partitioning scheme or because the basis sets in the ONIOM methods are not sufficiently flexible. As to the periodical trends, it is found that for the Co-group metal hydrides, the hydricities increase in the order second row < third row < first row. For the Ni-group metal hydrides, the hydricities increase in the order second row ≈ third row ≪ first row. As to the effects of the phosphine ligands, it is found that a dual-parameter equation can quantitatively predict the hydricities, where the two parameters are the NBO charge of the phosphorus and the natural bite angle of the diphosphine. Finally, no correlation is found between the hydricity and the metal−hydrogen vibration frequency or the hydrogen chemical shift. Therefore, it is not reliable to use any vibrational spectrum or proton NMR method to estimate the hydricity of transition-metal hydrides.

Influence of substituents on the infrared stretching frequencies of carbonyl group in esters of benzoic acid

AbstractInfrared spectra of 25 substituted phenyl esters of benzoic acid C6H5CO2C6H4‐X (XH, 3‐Cl, 3‐F, 3‐CN, 3‐NO2, 3‐CH3, 3‐OH, 3‐NH2, 4‐Cl, 4‐F, 4‐NO2, 4‐CN, 4‐OCH3, 4‐CH3, 4‐NH2, 2‐Cl, 2‐F, 2‐I, 2‐NO2, 2‐CF3, 2‐CN, 2‐CH3, 2‐OCH3, 2‐N(CH3)2, 2‐C(CH3)3), 8 alkyl benzoates C6H5CO2R (XCH3, CH2CH3, CH2Cl, CH2CN, CH2CCH, CH2CH2Cl, CH2CH2OCH3, CH2C6H5), and 22 phenyl esters of substituted benzoic acids X‐C6H4CO2C6H5 (X3‐Cl, 3‐NO2, 3‐CH3, 3‐N(CH3)2, 4‐F, 4‐Cl, 4‐Br, 4‐NO2, 4‐CH3, 4‐C(CH3)3, 4‐OCH3, 4‐NH2, 2‐Cl, 2‐F, 2‐Br, 2‐I, 2‐NO2, 2‐CN, 2‐CF3, 2‐CH3, 2‐OCH3, 2‐NH2) were recorded in tetrachloromethane in the region of 400–4000 cm−1. Carbonyl stretching frequencies νCO for meta‐ and para‐substituted phenyl esters of benzoic acid and phenyl esters of meta‐substituted benzoic acids were shown to correlate with the substituent constants σo. The influence of the through resonance effect on νCO was found to be important in the case of +R para substituents in the benzoyl part of phenyl benzoates as well. The carbonyl stretching frequencies of ortho derivatives in phenoxy part were shown to correlate with the inductive substituent constant σI only. In the benzoyl part of the esters the carbonyl stretching frequencies of cis and trans conformers (relative to the carbonyl group) of ortho derivatives were nicely described by dual parameter equations: (νCO)cis = (νCO)o + c1σI + c3 $E_{\rm s}^{\rm B} $and (νCO)trans = (νCO)o + c1σp+ + c3 $E_{\rm s}^{\rm B} $ (R = 0.99). The trans isomers of phenyl esters of ortho‐substituted benzoic acids showed direct resonance similar to that for para derivatives. The positive steric term found for both the cis and trans conformers could be considered as measure of the steric inhibition of resonance between the phenyl ring and the carboxy‐group caused by bulky ortho substituents. The existence of cis/trans conformations was supported by frequency calculations with Density Functional Theory (DFT) method at B3LYP/6‐311+G** level for the ortho‐substituted benzoates. In the case of alkyl benzoates good correlations of νCO values were obtained when both the Taft σ* and the steric $E_{\rm s}^{\rm B} $ constants were used. For meta‐ and para‐substituted phenyl benzoates s‐trans conformation where the plane of the benzene ring in the benzoyl part of the ester is coplanar with the carbonyl bond plane and the plane of the benzene ring in the phenoxy part is twisted nearly perpendicular relative to the carbonyl bond plane was supported. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Aromatic hydroxylation by cytochrome P450: model calculations of mechanism and substituent effects.

The mechanism and selectivity of aromatic hydroxylation by cytochrome P450 enzymes is explored using new B3LYP density functional theory computations. The calculations, using a realistic porphyrin model system, show that rate-determining addition of compound I to an aromatic carbon atom proceeds via a transition state with partial radical and cationic character. Reactivity is shown to depend strongly on ring substituents, with both electron-withdrawing and -donating groups strongly decreasing the addition barrier in the para position, and it is shown that the calculated barrier heights can be reproduced by a new dual-parameter equation based on radical and cationic Hammett sigma parameters.

Correlation analysis of UV spectral data of some phenylhydrazones and semicarbazones by the dual-parameter equation. Observation of three types of behaviors of the ?max values induced by the polar effects of substituents

The K-band λmax values of the UV spectra of five types of p-Y-benzaldehyde derivatives, namely phenylhydrazones (1-Ys), 2,4-dinitrophenylhydrazones (2-Ys), 4-nitrophenylhydrazones (3-Ys), semicarbazones (4-Ys) and N-phenylsemicarbazones (5-Ys), were measured and the corresponding wavenumbers (νmax) calculated. Correlation analyses of the νmax values by the dual-parameter equation show that the νmax values of these compounds are affected, albeit to different degrees, by both spin-delocalization effects (σ˙) and polar effects (σx) of the substituents. The spin-delocalization effects of substituents always facilitate bathochromic shifts of the λmax values (ρ˙ negative). However, polar effects of the substituents on these λmax data depend on the mode of polarization of these hydrazone or semicarbazone molecules, i.e. electron-pair acceptor substituents (Ys) facilitate bathochromic shifts for 1-Ys (ρx negative), but hypsochromic shifts for 2-Ys and 3-Ys (ρx positive), and induce very small shifts for 4-Ys and 5-Ys. As expected, donor Ys facilitate hypsochromic shifts for 1-Ys and bathochromic shifts for 2-Ys and 3-Ys and induce very small shifts for 4-Ys and 5-Ys. Possibly, a higher degree of polarization of the substrate molecule would demand a higher degree of polar assistance from the substituents at the transition states. © 1998 John Wiley & Sons, Ltd.

Application of the Dual Parameter Equation to the Correlation Analysis of the Redox Potential Data of Five para-Substituted Phenyl Compounds

Dual-parameter correlation analysis of the redox potential data of five aromatic compounds shows that the transition states of the polarographic processes are affected by the spin-delocalization effect in addition to the polar effect of the substituents.

Donor Complexes of Silylene, Germylene, and Stannylene

AbstractThe complexes of various donor molecules, AH3 (A = N, P, As, Sb, Bi) and AH2 (A = 0, S, Se, Te) with silylene, germylene, and stannylene (1Al ground state) were studied by means of quantum chemical investigations at ab initio level utilizing all valence electron basis sets and relativistic corrected effective core potential methods. Accordingly, the donor molecules are weakly bound, the association energies are in the range of 15–30 kcal per mole. The exothermic energies for adduct formation, i.e., the resulting binding energies for the donor complexes, decrease in the order silylene &gt; germylene &gt; stannylene. The population analysis indicates for NH3 and BiH3 only a weak bonding towards the XH2 fragment (X =Si, Ge, Sn) while the higher homologues (A = P, As, Sb) form ylide structures, 1.2‐dipolaric in nature. The addition of two donor molecules has been studied for silylene and is much less favourable than donor mono‐addition. For the donor mono‐addition a dual parameter relationship between (a) the HOMO energies of the donor (n‐orbital of the AH3 unit, n, p‐orbitals for AH2) and (b) the covalent bond energies (from the literature) versus the binding energies of the donor‐acceptor compounds was examined. This dual parameter equation describes satisfactorily the essential features of the stabilities of the donor‐acceptor structures.

The nucleophilic silyl radical: Dual-parameter correlation analysis of the relative rates of bromine-atom abstraction reactions as measured by a rigorous methodology

the relative rates [ kR(Y) values ] of bromine-atom abstraction reactions of 13 p-Y-substituted benzyl bromides (1-Y's : YH, Et, tBu, Me3Si, MeS, Ph, F, Cl, Br, CF3, CN, CO2Me, SO2Me) by tris(trimethylsilyl) silyl radicals [(Me3Si)3Si•] in cyclohexane at 80 °C have been measured by a rigorous methodology. Correlation analysis of the kinetic data by the dual-parameter equation (log kykH = ϱxσx+ϱ•σ•) shows that the silyl radical is distinctly nucleophilic and the transition states of the bromine-atom abstraction reactions are affected by both the polar and spindelocalization effects of the Y-substituents. Comparison of the |ϱpϱJJ•| values suggests that the contribution of the spin-delocalization effects in this Br-atom abstraction reaction may be greater than the spin-delocalization effects in some H-atom abstraction reactions.

The electrophilic trifluoromethyl radical cf 3 application of the dual-parameter equation to the correlation analysis of relative rates of the trifluoromethylbromo addition reactions to 14 p-y-substituted phenylacetylenes

A rigorous procedure was applied to the measurement of the relative rates, i.e., k r(Y) = k Y/ k H, of the trifluoromethylbromo addition reactions to 14 p-Y-substituted phenylacetylenes ( 1-Y, with Y =F, Cl, Br, Me, Bu, OMe, SMe, SiMe 3, CF 3, CN, NO 2, SOMe, COMe and CO 2Me) . The reaction was run in cyclohexane under nitrogen at 55 ±0.5 °C and was initiated by di-t-butylperoxy-oxalate. Correlation analysis of the data suggests that a spin effect is also operating at the transition state of this addition reaction and that the dual-parameter equation is applicable to this reaction.

Solvent Effects on Anchimerically Assisted Solvolyses. III. Solvent Effects on the Solvolyses of (1-Arylcycloalkyl)methyl p-Toluenesulfonates

Abstract The solvolysis rates of (1-arylcyclobutyl)methyl and (1-arylcyclopropyl)methyl p-toluenesulfonates were measured in a wide variety of solvents. The aryl-assisted kΔ solvolysis of [1-(p-methoxyphenyl)cyclobutyl]methyl p-toluenesulfonate did not give a linear Winstein–Grunwald correlation using the 2-adamantyl-based YOTs scale, but did show dispersion for different binary solvent mixtures. An extended dual-parameter treatment, log (k/k80E) = mcYOTs + mΔYΔ, successfully correlated the present set of kΔ solvolyses with R &amp;gt; 0.995 and SD &amp;lt; 0.09. The blending parameter MΔ (= 0.51mΔ/(mc + 0.51mΔ)) increases monotonically with increased electron donation by the substituent, showing an increased dispersion of the YOTs plot with increasing anchimeric assistance. The solvolysis of (1-arylcycloalkyl)methyl p-toluenesulfonates demonstrates the varying extent of anchimeric assistance by the neighboring groups, from a completely synchronous aryl-assisted process for the p-methoxy derivative of (1-phenylcyclobutyl)methyl p-toluenesulfonate, via moderately to weakly aryl-assistance by the p-methyl derivative and the unsubstituted compound, to a completely aryl-unassisted kc process for the more electron-withdrawing aryl derivatives and the (1-arylcyclopropyl)methyl p-toluenesulfonates. The dual-parameter equation enables one to monitor the varying extent of anchimeric assistance in the transition state. From the results we propose a general solvolysis framework involving a continuous spectrum of kc − kΔ mechanisms for anchimerically assisted solvolysis.

Should the dual-parameter equation be used in the correlation analysis of fluorescence spectral data of substituted styrenes and α-methylstyrenes?

The fluorescence spectra of 13 para-substituted styrenes (Y-STs) and ten para-substituted α-methylstyrenes (Y-MSTs) were recorded and correlation analysed by both the dual-parameter equation and the single-parameter equation. Very good correlations of the fluorescence energy ( ΔE) can be obtained by using the dual-parameter equation with the σ JJ scale in combination with either σ mb or σ +. Our results suggest that the singlet excited states of styrenes are diradical in nature as expected, and there is no need to use excited state substituent constants for this type of molecular species.

ChemInform Abstract: A Comparison of Single‐ and Dual‐Parameter Equations in the Correlation of Carbon‐13 Shifts in Substituted Styrenes.

Chemischer InformationsdienstVolume 17, Issue 10 Isocyclic Compounds ChemInform Abstract: A Comparison of Single- and Dual-Parameter Equations in the Correlation of Carbon-13 Shifts in Substituted Styrenes. C. D. SLATER, C. D. SLATERSearch for more papers by this authorC. N. ROBINSON, C. N. ROBINSONSearch for more papers by this authorR. BIES, R. BIESSearch for more papers by this authorD. W. BRYAN, D. W. BRYANSearch for more papers by this authorK. CHANG, K. CHANGSearch for more papers by this authorA. W. HILL, A. W. HILLSearch for more papers by this authorW. H. JUN. MOORE, W. H. JUN. MOORESearch for more papers by this authorT. G. OTEY, T. G. OTEYSearch for more papers by this authorM. L. POPPELREITER, M. L. POPPELREITERSearch for more papers by this authorJ. R. REISSER, J. R. REISSERSearch for more papers by this authorG. E. STABLEIN, G. E. STABLEINSearch for more papers by this authorV. P. III WADDY, V. P. III WADDYSearch for more papers by this authorW. O. WILKINSON, W. O. WILKINSONSearch for more papers by this authorW. A. WRAY, W. A. WRAYSearch for more papers by this author C. D. SLATER, C. D. SLATERSearch for more papers by this authorC. N. ROBINSON, C. N. ROBINSONSearch for more papers by this authorR. BIES, R. BIESSearch for more papers by this authorD. W. BRYAN, D. W. BRYANSearch for more papers by this authorK. CHANG, K. CHANGSearch for more papers by this authorA. W. HILL, A. W. HILLSearch for more papers by this authorW. H. JUN. MOORE, W. H. JUN. MOORESearch for more papers by this authorT. G. OTEY, T. G. OTEYSearch for more papers by this authorM. L. POPPELREITER, M. L. POPPELREITERSearch for more papers by this authorJ. R. REISSER, J. R. REISSERSearch for more papers by this authorG. E. STABLEIN, G. E. STABLEINSearch for more papers by this authorV. P. III WADDY, V. P. III WADDYSearch for more papers by this authorW. O. WILKINSON, W. O. WILKINSONSearch for more papers by this authorW. A. WRAY, W. A. WRAYSearch for more papers by this author First published: March 11, 1986 https://doi.org/10.1002/chin.198610177AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume17, Issue10March 11, 1986 RelatedInformation

A comparison of single- and dual-parameter equations in the correlation of carbon-13 shifts in substituted styrenes

A comparison of single- and dual-parameter equations in the correlation of carbon-13 shifts in substituted styrenes

Effects of neutral and anionic substituents on the carbonyl stretching bands of substituted methylbenzoates

Effects of neutral and anionic substitutents on frequencies (ν CO) and integrated intensities ( A CO) of the carbonyl stretching bands of substituted methylbenzoates (solvent dimethyl sulphoxide) have been studied in relation to Hammett's equation: satisfactory correlations have been found between ν CO and σ + constants, as well as by using the dual-parameter equations to Yukawa, Tsuno and Taft; A CO have been found to increase in cases of strong electron-releasing substituents. It has been found that constants of anionic substituents, determined on the basis of nitrile i.r. frequencies and intensities, reflect satisfactorily the effects of these substituents on ν CO and A CO of methylbenzoates.

Solvent dependence, metal ion catalysis and base catalysis of nitrito to nitro linkage isomerization of pentaamminenitritocobalt(III)

The spontaneous rate of nitrito to nitro isomerization of [(NH3),Co(ONO)]2+ spans two orders of magnitude for 16 solvents studied. The volume of activation is small and negative (from - 3.5 to -7 cm3 mol-1) for water, dimethyl sulfoxide, N-methylformamide and sulfolane. Combined with the observation of negligible competitive solvolysis, and of an isokinetic plot of ΔH‡ against ΔS‡, this indicates that isomerization is intramolecular in all solvents. The solvent dependence is interpreted in terms of a dual-parameter equation involving terms for the Lewis basicities (DN) and Lewis acidities and polarity (ET). By use of this approach both DN and ET of the solvents are shown to be major contributing factors to reactivity. Further studies on base-catalysed nitrito to nitro isomerizations reveal mild catalysis by F-, AcO- and Et3N in Me2SO. The metal ions HgZ+, Ag+ and Cd2+ also catalyse the isomerization in water [kHg 1.16 × dm3 mol-1 s-1, kAg 2.85 × dm3 mol-1 s-1, kCd 4.4 × 10-5 dm3 mol-1 s-1; ,μ 1.0 M (CIO4-), 25°C]. The lack of competition by AcO-, NO3- and H2O in the Hg2+-catalysed isomerization reaction also implicates an intramolecular process for this path. In acetone, the ions Hg2+, Ag+, Cd2+ and Zn2+ catalyse the isomerization reaction with a rate law of the form Kobs = Ks + Km[n+] except for Ag+, where the rate law takes the form Kobs = (ks + kK[Ag+])/(1 + K[Mn+]) with kAg = kK = 2.11 × dm3 mol-1 s-1, k = 1.74 × 10-4 s-1 and K = 12 ± 1 dm3 mol-1. The limiting rate is ascribed to a high stability constant for the silver adduct intermediate. The analogous RhIII and IrIII complexes also exhibit catalysis by Ag+ and Hg2+ in aqueous solution.

Effect of substituents on the kinetic energy release in unimolecular decompositions of substituted anisoles

AbstractThe kinetic energy relased on the loss of a CH3 ⋅ radical from para substituted anisoles appears to depend on the nature of the substituent. The application of the dual parameter equation of Yukawa and Tsuno yields a linear correlation with the T0.5‐values. The mesomeric effect predominates strongly over the inductive effect.