Marek K. Kalinowski

Solvent effect on the redox potential of quinone-semiquinone systems

Abstract Polarographic reduction of 1,4-benzoquinone, 1,4-naphthoquinone, 9,10-phenanthrenequinone and 9,10-anthraquinone was studied in pyridine, acetone, hexamethylphosphoramide, dimethylformamide, dimethylacetamide, acetonitrile, dimethylsulfoxide and propylene carbonate. The variation of the E1/2-values proper for the first electron transfer step (measured against oxidation potential of ferrocene) with the properties of solvent is analyzed in terms of the donor-acceptor concept. Linear correlations of E1/2 vs. acceptor number are observed; the slopes of corresponding lines correlate with the spin densities at oxygen atoms of semiquinones.

Redox behaviour of phenothiazine and phenazine in organic solvents

Abstract The electroreduction of phenazine (PHN) and electro-oxidation of phenothiazine (PHT) in the potential region of the first waves have been examined by polarography and cyclic voltammetry in some organic solvents. Reversible processes , and , were identified in all the solvents under investigations. The large shifts in formal potentials ( vs ferrocene/ferricinium internal standard) are interpreted on the basis of Gutmanns donor—acceptor concept for solvent—solute interaction.

Electrochemical studies of ion pairs and triplets formed by alkali metal cations with 1,2-naphthosemiquinone and 1,2-naphthoquinone dianion

Abstract The properties of ion associates formed by alkali metal cations with 1,2-naphthosemiquinone radical anions and 1,2-naphthoquinone dianions have been polarographically studied in dimethylsulfoxide solutions. It was established that these radicals and dianions coexist in equilibria with corresponding ion pairs and triple ions. The values of association constants were calculated on the basis of the slightly modified method of De Ford and Hume. Some structural aspects of ion association in the systems investigated are discussed.

STABILITY OF 15-CROWN-5 AND BENZO-15-CROWN-5 COMPLEXES WITH ALKALI METAL CATIONS IN NONAQUEOUS MEDIA

Abstract The formation of alkali metal cation complexes with 15-crown-5 and benzo-15-crown-5 in ten organic solvents has been investigated by cyclic voltammetry at 25°C. Stability constants of the resulting 1 : 1 complexes have been determined by monitoring the shift in reduction potentials of the cations against ligand concentration. Based on the results obtained the dependences of stabilities of the complexes on Gutmann donicity of the solvents and on standard Gibbs transfer energies of the metal ion from water to a given solvent have been analyzed and discussed.

Electrostatic potentials of molecules and prediction of the lewis acid-base properties of solvents, part II. Application of electrostatic parameters

SummaryElectrostatic parameters,UN andUP, introduced previously, have been applied to predict solvent acid and base properties. TheUN parameter correlates well with the electrostatic component of solvent basicity. This parameter also significantly improves correlations between Koppel-Paju, Kamlet-Taft and Gutmann basicity scales. TheUP parameter combined with Mullikan charges at hydrogen atoms of the solvent molecules allows an estimation of solvent acidity parameters in the frame of the two-parameter similarity model. The results show that parameters computed with the MNDO method for isolated molecules are suitable for molecules of nonaqueous solvents in liquid state.ZusammenfassungDie in der vorhergehenden Arbeit eingeführten elektrostatischen ParameterUN undUP wurden zu Vorhersagen von Säure- und Base-Eigenschaften von Lösungsmitteln angewandt. DerUN-Parameter korreliert gut mit der elektrostatischen Komponente der Lösungsmittelbasizität und verbessert auch signifikant Korrelationen zwischen der Koppel-Paju, Kamelt-Taft und Gutmannschen Basizitätsskala. DerUP-Parameter, in Kombination mit Mullikan-Ladungen an den Wasserstoffatomen der Lösungsmittelmoleküle, erlaubt die Abschätzung von Solvens-Aciditäts-Parametern im Rahmen eines Zweiparameter-Vergleichsmodells. Die Ergebnisse zeigen, daß die über die MNDO-Methode für isolierte Moleküle berechneten Parameter zur Beschreibung von nichtwäßrigen Lösungsmitteln geeignet sind.

Visible absorption spectra of the phenothiazine radical cation and its 10-substituted derivatives

The visible absorption spectra for the phenothiazine radical cation and its 10-substituted derivatives (the substituents were methyl, phenyl, benzyl and cyclohexyl), generated electrochemically in acetonitrile solutions, are reported. Substituent effects on these spectra are considered in the frame of quantum chemical calculations using the MNDO method.ZusammenfassungDie Absorptionsspektren des elektrochemisch generierten Phenothiazinradikal-Kations und seiner 10-substituierten Derivate (Methyl, Phenyl, Benzyl und Cyclohexyl als Substituenten) wurden im sichtbaren Bereich vermessen. Die Substituenteneffekte werden im Rahmen der quantenchemischen MNDO-Methode diskutiert.

Electrochemical reduction of substituted nitrobenzenes in N,N-dimethylformamide containing proton donating agents: effect of the double layer on the basicity of the nitro group

Abstract The effect of seven carboxylic acids on the polarographic reduction of para-substituted nitrobenzenes in N,N-dimethylformamide has been investigated. In the presence of these acids a new cathodic wave (pre-wave) appears at more positive potentials than the normal wave of a reactant. Linear relationships have been found between ΔE 1 2 and the pKDMFa values of acids as well as between ΔE 1 2 and the σ substituent constants, where ΔE 1 2 = (Epre-wave 1 2 - Enormal wave 1 2 ). It is concluded that in all the cases studied the reduction proceeds via a hydrogen-bonded complex of 1:1 type formed between the nitro compound and the acid in the double layer. The effect of the double layer on the basicity of the nitro group is discussed.

Solvent–solute interaction. Solvent and supporting electrolyte effects in non-aqueous electrochemistry of tris(acetylacetonato)iron(III)

Abstract Tris(acetylacetonato)iron(III) has been studied in acetonitrile, propylene carbonate, acetone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethylsulfoxide, N,N-diethylformamide, methanol and ethanol employing polarographic and cyclic voltammetric methods. Reversible or nearly reversible one-electron waves were registered in all these solvents containing (C2H5)4NClO4, KClO4, NaClO4 and LiClO4 as background electrolytes. The polarographic half-wave potentials were found to vary with the nature of electrolyte cation; it has been observed that correlations between E 1 2 values and the reciprocal of cationic radius exist. Their slopes are dependent on the properties of solvents and correlate with the appropriate values of Gutmann donor numbers. All these observations are discussed in terms of the donor-acceptor concept for solvent-solute interaction.

Spectrophotometric studies on the solvatochromism of the Fe(CN)2(phen)2 complex

SummaryThe solvatochromic behaviour ofbis-(cyano)-bis-(9,10-phenanthroline)-iron(II) has been reexamined spectrophotometrically in a series of 19 solvents including water, alcohols and dipolar. aprotic media. Satisfactory correlations between the wave numbers of the long-wavelength band and solvent acceptor numbers are obtained in all media; only values, for carboxylic acids deviate from the regression line.ZusammenfassungDas solvatochrome Verhalten vonbis-(Cyano)-bis-(9,10-phenanthrolin)-eisen(II) wurde in 19 Lösungsmitteln, darunter Wasser, Alkohole und dipolare aprotische Medien, spektrophotometrisch überprüft. In allen Medien wurden zufriedenstellende Korrelationen zwischen den Wellenzahlen der langwelligen Bande und den Akzeptorzahlen der Lösungsmittel erhalten; lediglich die Werte für Carbonsäuren weichen von der Ausgleichgeraden ab.

Effect of carboxylic acids on the cathodic reduction of benzophenone in N,N-dimethyl-formamide. Polarographic and CNDO/2 studies

Effect of eight carboxylic acids on the polarographic reduction of benzophenone in N,N-dimethylformamide has been studied. In the presence of these acids, a new cathodic wave (“pre-wave”) appears at more positive potentials than the original wave of benzophenone. Linear correlation has been found between ΔE12 and the pKDMFa values of acids, where ΔE12  (Epre-wave12  Eoriginal wave12). It is suggested that in all the cases investigated the reduction proceeds via a hydrogen-bonded complex formed between the carbonyl compound and the acid in the double-layer. The structural aspects of the benzophenoneformic acid adduct have been solved using CNDO/2 method.