Wyniki wyszukiwania - BazTech

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Posadzki przemysłowe z betonu utwardzonego powierzchniowo i żywiczne

Nowacki A.

Materiały Budowlane

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2018

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nr 9

2--3

2

Synthesis of New Quaternary Ammonium Salts - Derivatives of Phenyl Glucopyranosides

Dmochowska B., Pellowska-Januszek L., Skorupa E., Nowacki A., Stock F., Stepnowski P., Wiśniewski A.

Polish Journal of Chemistry

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2006

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Vol. 80, nr 9

1513-1521

EN

A new series of quaternary ammonium tosylates - derivatives of phenyl beta-Dglucopyranoside - has been produced in reactions of phenyl 2,3,4-tri-O-acetyl- 6-O-tosyl-beta-D-glucopyranoside with triethylamine, trimethylamine, 4-(N,Ndimethylamino) pyridine, 2-methylpyridine and pyridine. The structures of the isolates were determined by spectral analysis, including extensive 2D NMR spectral analyses.

3

Wymagania techniczne nawierzchni do otwartych obiektów sportowych

Nowacki A.

Materiały Budowlane

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2006

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nr 9

26-27

4

Efekt anomeryczny

Nowacki A., Wiśniewski A.

Wiadomości Chemiczne

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2005

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[Z] 59, 7-8

613-638

EN

Conformational equilibrium of cyclohexane derivatives depends on the location of the substituents in carbocyclic ring. Equatorial location of non-hydrogen substituents dominate over axial one because in the latter case there exist unfavourable 1,3-diaxial interactions. The solvent effect on the equilibrium is well known. Diequatorial conformer of frara-l,2-dibromo-cyclohexane is favoured over the diaxial one in polar solvents, while diaxial conformer is favoured in non-polar solvents. Conformational equilibrium of cis-l,3-hexanediol is controlled by intramolecular hydrogen bond, whose strength depends on the solvent polarity. Replacement of one or more methylene groups by oxygen atoms in carbocyclic ring changes conformational equilibrium of variously substituted tetrahydropyrans or dioxane derivatives as is shown in Figs. 5 and 6. Conformational equilibrium of a-substituted tetrahydropyran depends on the structure and chemical character of the substituent. Electron-withdrawing groups favour axial orientation. This phenomenon is called encfo-anomeric effect, (AE) and is characteristic for compounds with C-X-C-Y structural fragment, where X is N, O or S and Y is F, Cl, Br, O, N or S. This effect is revealed in non-polar solvents, while the equatorial orientation of C-l -substituent is preferred in strongly polar solvents. The effect is associated with shortening of the X-C-l and elongation of the C-l-Y bonds. Hyperconjugation of the non-bonding orbital of oxygen atom and antibonding σ* orbital of the C-l-Y bond is responsible for this effect. Gibss free energy of the anomeric effect decreases in the order: halogen atom > OR > SR > OH > NH2 > C. Conformational or/and anomeric equilibrium of sugars and its derivatives is controlled by anomeric effect and so called instability factors (IF). Non-bonded interactions between groups in the sugar ring, i.e. IF, are well known and exhaustively discussed in the literature. In the molecules of glycosides and their derivatives apart from ewfo-anomeric effect, also exo-anomeric effect is present, which determines the spatial orientation of the aglycon in relation to the sugar ring. The latter effect concerns both anomers and favours such an aglycon orientation in which the dihedral angle O-5-C-1-O-1 C is +sc (for ar-D-anomer) and sc for B-D-anomer. The above mentioned arrangement enables hyperconjugation of non-bonding sp3 orbital of O-l (exo) atom with the antibonding orbital of O-5-C-1 bond. This effect is responsible for the spatial structure of some polysaccharides. Nitrogen substituents (especially those with a positive charge) and carbon substituents are preferably located in the equatorial orientation due to the so called reverse anomeric effect (RAE). This effect is characteristic for N-(glycopyranosyl)pyridinium, -imidazolium and similar salts. Some authors suggest that RAE does not exist and the equilibrium state of such compounds depends on the exo-anomeric or steric effects.