Benzenethiols: pK a Values Measured in Solutions Against Quantum Chemically Computed Gaseous-Phase Proton Affinities

Pankratov, A. N.; Shalabay, Alexei V.

doi:10.1080/10426500307847

Cited by 10 publications

(5 citation statements)

References 16 publications

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“…Therefore, they can hardly be described at a high level of theory using ab initio or DFT methods. On the other hand, we have found that the MNDO, AM1, and PM3 methods correctly reproduce the most important thermodynamic and molecular characteristics ( [16,[30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45], etc.) and the electronegativity, inductive, and mesomeric parameters of atomic groups [16,46,47] in…”

Section: Resultsmentioning

confidence: 97%

Analytical Azo Coupling Reactions: A Quantum-Chemical Consideration

Pankratov

2005

J Anal Chem

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The nitrite ion is a priority environmental toxicant and a precursor of N-nitrosamines, which are carcinogenic and mutagenic agents [1,2]. It interacts with oxyhemoglobin in blood to form methemoglobin, which disturbs cell respiration, and, therefore, the vital functions of the entire organism [3,4]. Nitrites are added to meat foods to improve vendibility. The analytical determination of nitrites and N-nitrosamines in foodstuff and other samples is a topical problem. The simplicity, availability, and satisfactory metrological characteristics of photometry make it one of the most suitable methods for solving this problem [5,6]. The most important photometric reactions for nitrites and N -nitrosamines are the diazotization of primary aromatic amines and the subsequent azo coupling reaction [5,6].In photometric analysis, the following processes in which or N -nitrosamines participate are used: (1) the self-coupling of 1-aminonaphthalene ( I ) through the diazotization of I followed by the coupling of the resulting naphthalene-1-diazonium cation ( II ) with I [5-8] and (2) the analytical Griess reaction involving the diazotization of 4-aminobenzenesulfonic (sulfanilic) acid followed by the azo coupling of the resulting 4-sulfobenzenediazonium with amine I [5,6,9].In an aqueous solution, the former of the processes mentioned above occurs to only a small extent and the product precipitates [7,8]. However, the yield of the analytical form and the stability of the analytical signal over time improve dramatically if the reaction is performed in microreactors [10], such as anionic surfactant (sodium dodecyl sulfate) micelles [7,8]. On the contrary, the Griess reaction is successfully performed in an aqueous medium [5,6], whereas anionic surfactant micelles only slightly enhance the analytical signal NO 2 -(increase the absorbance of the solution of the analytical form) and stabilize it over time [9].Note that the stability of an analytical signal and the thermodynamic stability of molecular systems discussed below are different concepts. The former is characterized by the time in which the maximum intensity of the analytical signal remains virtually constant, whereas the latter is characterized by the enthalpy and the free energy of formation of a certain molecule.In the diazotization-azo coupling tandem, the azo coupling reaction is crucial, because its products are the sources of the analytical signal in the photometric determination of nitrite and N -nitrosamines.According to [11], the self-coupling product of 1-aminonaphthalene I is 4-amino-1,1'-azonaphthalene resulting from the interaction of naphthalene-1-diazonium cation II with I at the 4-position of the amine molecule. At the same time, the possibility is discussed [11] for the formation of 1,1'-diazoaminonaphthalene (triazene) upon the electrophilic attack of the nitrogen atom in molecule I by cation II . The author of [11] reports nothing concerning the detection of 1-amino-2,1'-azonaphthalene (the result of coupling at position 2 of molecule I ).At the same tim...

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Section: Resultsmentioning

confidence: 97%

Analytical Azo Coupling Reactions: A Quantum-Chemical Consideration

Pankratov

2005

J Anal Chem

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“…We found that the MNDO, AM1, and PM3 methods correctly reproduce the most important thermodynamic and molecular characteristics [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47], electronegativities, and inductive and mesomeric parameters of groups of atoms [48,49] is series of compounds. Among these methods, only PM3 yields reasonable results for the heats of formation of nitroso compounds [24,30] and dimethyl sulfone [32].…”

Section: Resultsmentioning

confidence: 99%

Quantitative structure-property relationships in the series of diazonium cations, intermediate products in the synthesis of analytical forms and dyes

et al. 2005

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The azocoupling reaction of aromatic amines and phenols with aryldiazonium cations is of great importance for the production of dyes [1][2][3] and in analytical chemistry [4].Diazonium cations can be reduced either chemically or electrochemically [5][6][7][8][9][10][11][12]. For many compounds, the abilities to be subjected to electrophilic (nucleophilic) attack and to undergo oxidation (reduction) vary in parallel [13][14][15][16]. The susceptibility of diazo cations to reduction can serve as a measure of their electrophilic activity. Therefore, the a priori prediction of the reduction potentials and electron affinities of diazonium cations of the given structure and their subsequent directed synthesis is reasonable for the selection of the optimum reaction rates of the formation of azo dyes and analytical forms.Diazonium cations decompose to release molecular nitrogen [2,10,12,17]. To provide high yields of azo compounds and satisfactory accuracy, precision, and other performance characteristics of analytical procedures, it is desirable to avoid this competing reaction and to estimate quantitatively the degree of decomposition of newly synthesized diazonium salts.Among others, the stretching frequencies of the C -N + ≡ N group are a measure of the stability of diazonium cations (and simultaneously an indication of their activity as electrophilic agents) [17][18][19][20][21][22].As will be demonstrated below, vibrational frequencies and electron affinity correlate with the mesomeric dipole moments of substituents in aryldiazonium cations.The aim of this work was to find (based on quantumchemical calculations) quantitative structure-property relationships for the prediction of reduction potentials and some related quantities, electron affinities, stretching frequencies of the C -N + ≡ N group of aryldiazonium cations, and mesomeric dipole moments of groups of atoms.The correlations that are discussed in this work were presented in [23]. EXPERIMENTALCalculations were performed by the PM3 method [24] using the MOPAC program [25,26] with full geometry optimization (Broyden-Fletcher-GoldfarbShanno procedure [27]) using the Thiel algorithm for rapid minimization [28]. Preliminary optimization was performed by the molecular mechanics method (MMX procedure) [29] using the PCMODEL program [29]. In quantum-chemical calculations, we set the condition that the norm of the gradient was no higher than 0.084 kJ mol -1 Å -1 . In some cases, a sufficient decrease in the norm of the gradient was attained by the reject of Thiel rapid minimization (using the option NOTHIEL in the MOPAC program), by the optimization using the Davidon-Fletcher-Powell method (option DFP) [27], and by the combination of the approaches provided by the options NOTHIEL and DFP.For molecules with closed electronic shells, we used the restricted Hartree-Fock (RHF) method [26]. Radicals formed on the reduction of aryldiazonium salts were calculated by the unrestricted Hartree-Fock (UHF) method [26].Abstract -It was demonstrated that the reduction potentials,...

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Section: Resultsmentioning

confidence: 99%

Quantitative structure-property relationships in the series of diazonium cations, intermediate products in the synthesis of analytical forms and dyes

Pankratov

2005

J Anal Chem

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It was demonstrated that the reduction potentials, dimerization potentials, and half-equivalence point potentials in the titration of aryldiazonium cations XC 6 H 4 N + ≡ N are linearly related to the quantum-chemically calculated values of electron affinities ( A ) and stabilization energies of radicals formed in the reduction of diazonium cations. Linear correlations between the frequencies ( ν ) characterizing the set of stretching vibrations in the C -N + ≡ N fragment of XC 6 H 4 N + ≡ N cations and N ≡ N and C-N bond orders, charges on carbon atoms in the para positions of aromatic rings of C 6 H 5 X molecules, and mesomeric dipole moments ( µ m ) of substituents X were found. Quantitative relationships relating µ m and ν to A were revealed. These relationships have clear physical meaning, are characterized by relatively large correlation coefficients, and possess predictive power for redox properties, electron affinity, and vibrational spectra of aryldiazonium cations and mesomeric dipole moments of atomic groups in organic molecules.

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Benzenethiols: pK a Values Measured in Solutions Against Quantum Chemically Computed Gaseous-Phase Proton Affinities

Cited by 10 publications

References 16 publications

Analytical Azo Coupling Reactions: A Quantum-Chemical Consideration

Analytical Azo Coupling Reactions: A Quantum-Chemical Consideration

Quantitative structure-property relationships in the series of diazonium cations, intermediate products in the synthesis of analytical forms and dyes

Quantitative structure-property relationships in the series of diazonium cations, intermediate products in the synthesis of analytical forms and dyes

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