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The Influence of Structural Effects on the Complexing Ability of Crown Ethers III. Rubidium Complexes Formed by the Ligands of the 18C6 Typ

Filipek S., Krzyśko K., Kalinowski M. K.

Polish Journal of Chemistry

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2001

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Vol. 75, nr 12

1887-1893

EN

A combined AM 1 and molecular mechanics study of the complexation of the rubidium cation by nine substituted crown ethers, L, containing 18 atoms of macroring is presented. The role of microsolvation was incorporated into the models by studying the complexes surrounded by six methanol molecules. The substituent effect is related to the interaction energy, Eint, which was computed for the clusters LRb+(CH3OH)6 in their lowest energy conformations. This is demonstrated by the linear correlation found by plotting logKs vs. Eint, where Ks stands for stability constant of a complex. The appropriate Ks values were calculated on the basis of cyclic voltammetric measurements.

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Interaction of sodium and potassium ions with the cis isomers of dicyclohexyl-18-crown-6 in nonaqueous media

Wagner-Czauderna E., Filipek S., Kalinowski M.K.

Polish Journal of Chemistry

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1998

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Vol. 72, nr 10

2294-2302

EN

The formation constants, K-s for 1:1 complexes of the cis-syn-cis and cis-anti-cis isomers of dicyclohexyl-18-crown-6 with sodium and potassium cations have been electrochemically determined in 10 nonaqueous (protic and aprotic) media. Linear correlations were obtained for log K-s with standard Gibbs transfer energies of the cation from water to a given solvent. The cis-anti-cis isomer was found to be a weaker complexer than the cis-syn-cis one and this was elucidated in terms of the ligand solvation. Energy-minimized structures of the ligands and complexes suuuounded by methanol and acetonitrile molecules were established by molecular dynamics computations.

3

Electrochemical reduction of p-chloronitrobenzene in dipolar aprotic solvents containing carboxylic acids

Wagner-Czauderna E., Orłowska E., Kalinowski M.K.

Polish Journal of Chemistry

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1998

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Vol. 72, nr 9

2127-2133

EN

The effect of carboxylic acids of different strenght on polarographic behaviour of p-chloronitrobenzene in N, N-dimethylformamide has been investigated. In the presence of each acid a pre-wave appeared at a more positive potential than the original one, which was associated with the cathodic reduction of a hydrogen-bonded adduct, formed between the nitrocompound and the acid molecules in the double layer of the electrode. A linear correlation has been found between delta E-1/2 and pK(DMF/HA) (pK(DMF/HA) refers to the value of the pK-a measured in N, N-dimethylformamide, whereas delta E-1/2=E(pre-wave/1/2) - E(original wave/1/2)). Measurements in a solvent series in the presence of benzoic acid (BA) led to the correlation between delta E-1/2 and pK-BA (the symbol pK-BA denotes the value measured in a given solvent). The slopes of regression lines are discussed in terms of the double layer effect on the basicity of the -NO2 group.