Linear Free Energy Correlations Research Articles

The thermal cycloaddition of substituted thiobenzophenones with phenylallene: mechanism and linear free energy relationships of reaction rates

The reaction rates for the thermal cycloadditions of substituted thiobenzophenones with phenylallene in CH3CN at 40 °C were determined and analysed by linear free energy correlations. Using a Hammett-type relationship, the best correlations were obtained with the σ–-parameter (ρ–= 1.09 ± 0.06) indicating that, in the transition state, mesomeric interaction occurs between –M substituents and an electron-releasing reaction centre. The small ρ–-value is in agreement with a 1,4-diradical intermediate in a (π2s+π2s+π2s)-cycloaddition.Separate correlation of electron-donating and electron-withdrawing substituents gives rise to two lines with different slopes, each with a much better correlation coefficient and ψ. This observation indicates that the thione system is relatively more senstive to electron-donating substituents than to electron-withdrawing substituents i.e. a π-repulsive saturation interaction occurs with the π-acceptor thiocarbonyl function. Additional analysis with Charton's DSP-equation (ρR/ρ1= 1.82) shows that the contribution of resonance effect is 69% and the contribution of inductive effect is 31%. Bromilow's DSP–non-linear resonance effect equation yields a value of +0.38 ± 0.01 for the electron demand parameter', indicating the enhanced responance interaction of electron-acceptor substituents with the thione system in the transition state. An inverse secondary isotope effect on the rate constant of disapperance of thione during the reaction with PhCHCCH2, PhCDCCH2, and PhCDCCD2 was observed; k2(Hα)/k2(Dα)= 0.91 ± 0.02 and k2(2Hγ)/k2(2Dγ)= 0.75 ± 0.01. These values are less than unity and consistent with attack at C-β and indicative for a change in hybridization at C-α and C-γ. The observed isotope effect when using D3CO-CHCCH2 instead of H3CO-CHCCH2, k2(H)/k2(D)= 1.20 ± 0.02 represents a rotational isotope effect arising from an increase in mass on substitution of hydrogen by deuterium. Experiments with an optically active allene (+)-PhC(H)CCHBut yielded products which were optically inactive, which points to a non-chiral intermediate i.e. the allylic diradical. We observed also a low solvent effect which is in agreement with the reaction mechanism i.e. a 1,4-diradical-mediated (π2s+π2s+π2s)-cycloaddition.

Active site mechanics of liver microsomal cytochrome P-450

For a set of 10 para-substituted toluene derivatives, three enzymatic constants were determined describing their interaction with purified rabbit liver microsomal P-450 LM2. The three constants were the catalytic rate constant ( k cat) for hydroxylation, the apparent dissociation constant ( K d) for the enzyme-substrate complex, and the interaction energy (ΔG int) between the substrate-binding and spin-state equilibria. The para-substituents of the toluene substrates were: hydrogen, fluoro, bromo, chloro, iodo, nitro, methyl, cyano, isopropyl, and t-butyl. Linear free energy correlations were sought between the enzymatic constants and several physical constants of the individual substrate molecules. These correlations would be useful both for empirical prediction purposes and for insight into active site chemistry and mechanics. Catalytic rates were correlated by a linear combination of the Hansch π hydrophobic constant and the Hammett σ value. A deuterium isotope effect ( D V) of 2.6 for d 8-toluene compared to d 0-toluene confirmed that hydrogen abstraction was partially rate-limiting with this series of substrates. Apparent dissociation constants were predicted by a linear combination of the molar volume and π, while the spin-state interaction energies were best predicted by a linear combination of the Hansch π hydrophobic constant and the reciprocal of the dielectric constant.

A study of tautomerism in diazonium coupling products of 4‐hydroxycoumarin

AbstractThe spectra (1H nmr, ir and uv) of a series of 3‐arylazo‐4‐hydroxycoumarins 1a‐m indicate that such compounds exist predominantly in the keto hydrazone form 1A both in solid state and in solution. The acid dissociation constants of the series studied were determined spectrophotometrically in 80 vol% ethanol‐water mixture at 27° and ionic strength of 0.1. The results of the correlations of these constants by Hammett and Yukawa‐Tsuno equations exclude the presence of the hydroxyazo form 1B in equilibrium with 1A in agreement with the spectral data. Also, the HMO method has been used to study tautomerism in such compounds. The results are also in full agreement with both the spectral and linear free energy correlations, the hydrazone form 1A being the most stable. It is further shown that both the intermolecular and intramolecular hydrogen bonding favor the hydrazone tautomer.

The distribution of divalent trace elements between sulfides, oxides, silicates and hydrothermal solutions: I. Thermodynamic basis

Experimental data for the standard Gibbs free energies of formation from the elements of a wide variety of metal sulfides and oxides, spinels, olivines and pyroxenes at 25°C and 1 bar define linear correlations, within about ±900 cal· mole −1, with the corresponding conventional standard partial molal Gibbs free energies of formation of the aqueous M 2+ cations of the form ΔG f, m DZ 0 = a m DZ ΔG fM 2+ 0+b M DZ where a M a Z and b M a Z are empirically determined constants characteristic of the structure M nZ. The only exceptions to correlations of this type are compounds of the heavy alkaline earths Ca, Sr and Ba, which appear to follow correlations with cation radius instead. The linear free energy correlations enable prediction of standard Gibbs free energies of formation of compositional end-members of a particular structure M nZ provided that a M a Z and b M a Z are known accurately. When only the free energy of the Mg end-member is known, the standard Gibbs free energy of formation at 25°C and 1 bar of the Fe endmember, and hence a M a Z and b M a Z Can be predicted from the temperature independence of a M aZ a otivine and estimated entropies and heat capacities for the Fe end-member. Using this approach, the free energies of ferrosilite, hedenbergite and annite at 25°C and 1 bar were predicted to within ±1000 cal· mole −1 of the helgeson et al. (1978) values. Free energies of formation of talc (M 3Si 4O 10(OH) 2), clinchlore (M 5Al 2Si 3O 10(OH) 8), and tremolite (Ca 2M 5(Si 4O 11) 2(OH) 2)-type compounds where M is Mg, Mn, Zn, Fe, Co, or Ni were then predicted at 25°C and 1 bar. Calculation of the equilibrium distribution of Mg, Zn and Sr between galena and hydrothermal solution, and Zn, Mg, Fe and Mn between chlorite and hydrothermal solution demonstrates: (1) that the Sr contents of low temperature galenas ( e.g. Mississippi Valley-type) should be negligible (reported analyses of Sr content and Sr isotopic composition of such galenas are probably attributable to fluid inclusions or carbonate inclusions); and (2), that the Zn contents of hydrothermal chlorites in a model of the midoceanic ridge hydrothermal systems are sensitive to temperature, to complexing in the aqueous phase, and to the overall Fe/Mg ratio of the chlorite.

Mononuclear heterocyclic rearrangements. Part 12. Kinetic study of substituent effects on the rearrangement of the (Z)-phenylhydrazones of some 5-aryl-3-benzoyl-1,2,4-oxidiazoles into 4-aroylamino-2,5-diphenyl-1,2,3-triazoles in dioxane–water at various pS+values

The kinetics of the title reaction have been studied in the pS+ range 4.0–12.0, at various temperatures. The logarithmic kinetic constants show excellent linear free energy correlations with σ and σn for the pS+- independent and pS+-dependent ranges, respectively. The susceptibility constants obtained (p+0.85 and +1.75, at pS+ 4.50 and 10.00, respectively) show that a larger negative charge is developed in the transition state of the base-catalysed reaction pathway than in that of the uncatalysed, pS+-independent route.

Linear free energy correlations for reversible dioxygen binding of a cobalt-porphyrin complex: a solvent effect study

On etudie dans plusieurs solvants la capacite de fixation de O 2 par Co(T(p-CH 3 O) PP)B ou T(p-CH 3 O)PP est le dianon de la tetraparamethoxyphenyl porphyrine et B est la pyridine, la piperidine et le methyl-1 imidazole

Hydride transfer reactions. Substituent effects in oxidation of N-benzylacridans by π acceptors

The kinetics of oxidation of a series of eight N-(substituted benzyl)acridans (3, NBA's) by 1,4-benzoquinone (BQ), p-chloranil (CA), 2,3-dicyano-1,4-benzoquinone (DCBQ), 7,7,8,8-tetracyanoquinodimethane (TCNQ), and tetracyanoethylene (TCNE) in acetonitrile (AN) and by BQ in 50:50 (v/v) AN-water were measured at 25 °C. Equilibrium constants for pseudobase formation, [Formula: see text], from the corresponding acridinium ions (4) were measured in water at 25 °C. Hammett correlations of the second-order rate constants for reaction of the NBA's without ortho substitutents (3a–e) led to ρ values of −0.29 (BQ, AN), −0.55 (CA), −0.56 (DCBQ), −0.64 (TCNQ), −0.41 (TCNE), and −0.47 (BQ, 50:50 AN–water). The second-order rate constants for 3a–e also give good linear free energy correlations with the [Formula: see text] values of 4a–e. These correlations and the [Formula: see text] values for the ortho-substituted acridinium ions (4f, g, h) are used to calculate rate constants for oxidation of the corresponding ortho-substituted NBA's (3f, g, h). The rate constants calculated in this way are 4.7 to 6.6 times and 6.4 to 12 times larger, respectively, than the observed rate constants for N-(2,4,6-trimethylbenzyl) and N-(2,6-dichlorobenzyl)acridan (3g and h). The variations in ρ values are attributed mainly to differences in the amount of electrostatic stabilization in the transition state resulting from differences in the separation of donor and acceptor and the degree of delocalization of the negative charge. The rate retarding effect of a pair of ortho substituents is attributed to sterie effects in a preferred face-to-face transition state.

Thermal [ π2 s+ π2 s+ π2 s]-cycloaddition of thiobenzophenone to substituted phenylallenes. Hammett correlation of rates and ionization energies

Thiobenzophenone reacts as an electrophile in the thermal [ π2 s+ π2 s+ π2 s]-cycloaddition reaction with substituted phenylallenes, was deduced from a linear free energy correlation of the reaction rates σ + (ϱ + = −0.36 ± 0.03 (n=9, r=0.97)) and with the first ionization energies IE a (log(k X/k H) = −0.55 IE a + 4.57 (r=0.92)) of the substituted phenylallenes. Additional evidence for the mechanism is given.

ChemInform Abstract: ELECTRONIC EFFECTS IN TRANSITION‐METAL PORPHYRINS. 4. EFFECT OF UNSYMMETRICAL L PHENYL SUBSTITUTION ON THE NMR SPECTRA OF A SERIES OF METAL‐FREE AND ZINC TETRAPHENYLPORPHYRINS

AbstractDie metallfreien Verbindungen (I) wurden nach einer abgewandelten Literaturmethode durch Reaktion von Pyrrol und je einem Äquivalent p‐Diethylaminobenzaldehyd und p‐Chlorbenzaldehyd in Propionsäure unter Rückfluß dargestellt.

ChemInform Abstract: CAVEAT ON THE USE OF LINEAR FREE ENERGY CORRELATIONS WITH Σ OR Σ+ TO DISTINGUISH TRANSITION‐STATE TYPES. A USEFUL GRAPHIC FOR THE SELECTION OF SUBSTITUENTS FOR A LINEAR FREE ENERGY STUDY

Chemischer InformationsdienstVolume 13, Issue 19 Article ChemInform Abstract: CAVEAT ON THE USE OF LINEAR FREE ENERGY CORRELATIONS WITH Σ OR Σ+ TO DISTINGUISH TRANSITION-STATE TYPES. A USEFUL GRAPHIC FOR THE SELECTION OF SUBSTITUENTS FOR A LINEAR FREE ENERGY STUDY R. E. GAWLEY, R. E. GAWLEYSearch for more papers by this author R. E. GAWLEY, R. E. GAWLEYSearch for more papers by this author First published: May 11, 1982 https://doi.org/10.1002/chin.198219081AboutPDF 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 onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume13, Issue19May 11, 1982 RelatedInformation

Caveat on the use of linear free energy correlations with .sigma. or .sigma.+ to distinguish transition-state types. A useful graphic for the selection of substituents for a linear free energy study

Caveat on the use of linear free energy correlations with .sigma. or .sigma.+ to distinguish transition-state types. A useful graphic for the selection of substituents for a linear free energy study

Alpha-Chymotrypsin deacylation: temperature dependence of hydrolysis and transesterification reactions.

The hydrolysis and transesterification reactions of furoyl-chymotrypsins display nonlinear Arrhenius plots with no apparent discontinuities. Of a number of models considered, the best explanation assumes a temperature-dependent rapid equilibrium between two forms of acyl-enzyme with differing reactivities. Rate constants for the transesterification of alpha-chymotrypsinyl 2-(5-n-propyl)furoate, after normalization for this equilibrium, display a linear free energy correlation with the Taft polarity constants sigma* and volumes of the attacking alcohols.

Commentary on the Kamlet-Taft Scale of Solvent Polarity for Aprotic Lewis Bases

The generalized scale of solvent polarity (r*) developed by Kamlet and Taft was justified originally from a modified form of reaction field theory. However, results from critical statistical tests demonstrate that such a rationalization of the -* scale is inadequate for both nonpolar and polar aprotic solvents. By contrast, the McRae treatment of dispersive and dipolar interactions between the solute and solvent provides a more suitable model for interpreting the seemingly general characteristics of the ir* numbers when these are used in linear free energy correlations. Several derived functions correlating medium effects to spectral changes and reaction kinetics for inorganic species have utilized the bulk dielectric constant and index of refraction as the variables representing the essential properties of the solvent. In an extensive critical review of literature sources Fowler, Katritzky and Rutherford (1971) noted the limitations on such single parameters when used as independent probes of solvent-solute interactions. As an alternative approach, a number of investigators have proposed various empirical parameters which are seemingly related to solvent polarity; and, among the more recent of these, the multiparameter system of Kamlet, Abboud, and Taft (1977) appears to be the most successful in interpreting a broad range of observed solvent effects upon reactions. The general linear free energy function in equation I relates the three Kamlet-Taft numbers for a given solvent to the observable property P and its specified reference state P).

Comments on “predicting gas phase organic molecule reaction rates using linear free energy correlations. I. O(3P) and OH addition and abstraction reactions”

Comments on “predicting gas phase organic molecule reaction rates using linear free energy correlations. I. O(³<i>P</i>) and OH addition and abstraction reactions”

Reply to “comments on ‘predicting gas phase organic molecule reaction rates using linear free energy correlations. I. O(3P) and OH addition and abstraction reactions’”

Reply to “comments on ‘predicting gas phase organic molecule reaction rates using linear free energy correlations. I. O(³<i>P</i>) and OH addition and abstraction reactions’”

Electron donor-acceptor complexes. 1. Linear free energy correlation of the charge-transfer transition energy with the kinetics of halogenolysis of alkylmetals

Electron donor-acceptor complexes. 1. Linear free energy correlation of the charge-transfer transition energy with the kinetics of halogenolysis of alkylmetals

A linear free energy correlation between solvent parameter E T(30) and stereoselectivity in the condensation of phenylmagnesium bromide with (±)-3-phenylbutanone.

A direct influence of the solvent on the RS,SR/RR,SS ratio in nucleophilic additions of phenylmagnesium bromide to (±)-3-phenylbutanone is reported.

Kinetics and mechanism of oxidation of tris-(1,10-phenanthroline)iron(II) by chlorine and bromine and of the reduction of tris-(1,10-phenanthroline)iron(III) by iodide ions

The rates of the oxidation of tris-(1,10-phenanthroline)iron(II) by chlorine and bromine, and of the reduction of tris-(1,10-phenanthroline)iron(III) by iodide ions have been measured at ionic strength I = 1.0 mol dm−3 (LiClO4). All the reactions obey second-order rate law:[Formula: see text]The activation parameters for the reactions are: Fe(Phen)32+/Br2: ΔH≠ = (64.2 ± 3.2) kJ mol−1, ΔS≠ = −(24.9 ± 1.5) J mol−1 K−1. Fe(Phen)33+/I−:ΔH≠ = (39.8 ± 2.1) kJ mol−1, ΔS≠ = −(19.7 ± 0.8) J mol−1 K−1.The reactions of tris-(1,10-phenanthroline)iron(II) with chlorine and bromine are unaffected by chloride, bromide, and acid. The proposed mechanism for these reactions involves a series of one-electron changes, with the species X2− (X = Cl, Br) as reaction intermediates, since good linear free energy correlations for the primary step, resulting in the formation of X2−, are obtained. The reduction of tris-(1,10-phenanthroline)iron(III) by iodide ions is catalysed by bromide and chloride ions, whereas the reduction of aquoiron(III) by iodide ions is known to be inhibited by bromide and chloride ions. A mechanistic interpretation of this observation is suggested.

Acid-catalyzed hydrolysis of N-vinylacetamides (enamides). Substituent effects of the acetamido and amino groups and linear free energy correlations of cyclohexene reactivities

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAcid-catalyzed hydrolysis of N-vinylacetamides (enamides). Substituent effects of the acetamido and amino groups and linear free energy correlations of cyclohexene reactivitiesV. M. Csizmadia, K. M. Koshy, K. C. M. Lau, R. A. McClelland, V. J. Nowlan, and Thomas T. TidwellCite this: J. Am. Chem. Soc. 1979, 101, 4, 974–979Publication Date (Print):February 1, 1979Publication History Published online1 May 2002Published inissue 1 February 1979https://doi.org/10.1021/ja00498a029RIGHTS & PERMISSIONSArticle Views410Altmetric-Citations17LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (693 KB) Get e-Alerts Get e-Alerts

Electronic substituent effects upon properties of 5-substituted-2-formylpyridine thiosemicarbazones and their metal complexes

The protonation constants of several 5-substituted-2-formylpyridine thiosemicarbazones, formation constants for their copper complexes, adduct formation constants of these complexes with ethylenediamine, protonation constants of the copper complexes, and half-wave reduction potentials of the copper and corresponding iron complexes have been determined. The electronic effect of substituents has been examined through the calculation of linear free energy correlations utilizing Hammet substituent constants as the independent parameter in the relationships. The effect of substituents upon the pharmacological properties of thiosemicarbazones is reconsidered here. The current results are used to suggest new experiments involving the reaction of 5-substituted-2-formylpyridine thiosemicarbazonato copper(II) complexes with Ehrlich cells.