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Wyszukujesz frazę "crystal structures" wg kryterium: Temat


Wyświetlanie 1-3 z 3
Tytuł:
Transformacje strukturalne w kryształach wywołane reakcjami fotochemicznymi
Structural transformations in crystals induced by photochemical reactions
Autorzy:
Turowska-Tyrk, I.
Bąkowicz, J.
Powiązania:
https://bibliotekanauki.pl/articles/171650.pdf
Data publikacji:
2014
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
reakcje fotochemiczne w kryształach
struktura kryształu
struktura cząsteczki
zmiany strukturalne
rentgenowska analiza strukturalna
krystalografia
photochemical reactions in crystals
crystal structures
molecular structure
structural changes
X-ray structure analysis
crystallography
Opis:
Structural changes induced in crystals by photochemical reactions were presented. The changes concern: a) the distances between neighbouring reactant molecules and their mutual orientation in the case of intermolecular reactions, b) the distances and angles between fragments of a molecule for intramolecular reactions, c) the position of molecules in crystals, d) geometry of hydrogen bonds, e) cell constants, and f) the content of product molecules in crystals. For most intramolecular reactions, the distances between reactive atoms are constant for a long time in phototransformation and decrease rapidly at its end (Figs. 3 and 5). In the case of intermolecular reactions, the distances between reactive atoms of reactant molecules decrease linearly along with the phototransformation of crystals (Fig. 7). Additionally, unreacted molecules become, to a certain degree, similar to product molecules in terms of their shape (Figs, 4 and 8). Reactant and product molecules do not assume a fixed place in crystals. Product molecules change their orientation towards that of which is observed in a pure product crystal and reactant molecules gradually move away from the position they took in pure reactant crystals. All this has an influence on the geometry of hydrogen bonds existing in crystals (Fig. 9). The above-mentioned structural transformations find their expression in values of cell constants (Fig. 10). The factors influencing the photoreactivity of molecules in crystals were also described. Knowledge of crystal and molecular structures of partly reacted crystals, determined thanks to X-ray structure analysis which is a branch of crystallography, reveals the behaviour of molecules in crystals in which photochemical reactions proceed and helps to understand a pathway of these reactions.
Źródło:
Wiadomości Chemiczne; 2014, 68, 5-6; 381-402
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Borowce jako centra kwasów Lewisa w oddziaływaniach międzycząsteczkowych : porównanie z wiązaniami wodorowymi
Triels as centers of Lewis acids in intermolecular interactions : comparison with hydrogen bonds
Autorzy:
Grabowski, S. J.
Powiązania:
https://bibliotekanauki.pl/articles/172397.pdf
Data publikacji:
2017
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
wiązanie wodorowe
wiązanie borowcowe
potencjał elektrostatyczny
dziura σ
dziura π
przesunięcie ładunku elektronowego
struktury krystaliczne
hydrogen bond
triel bond
electrostatic potential
σ-hole
π-hole
electron charge shift
crystal structures
Opis:
The triel bonds are analyzed and compared with the hydrogen bond interaction. The triel bonds belong to the class of interactions that are named as the σ-hole and π-hole bonds. The σ-hole bond is an interaction between the σ-hole characterized by the positive electrostatic potential and the electron rich regions such as lone electron pairs, π-electron systems, in other words, centers paying a role of Lewis bases. The σ-holes may be observed for elements of the 14–18 groups of the periodic system and the corresponding interactions with Lewis bases are named; tetrel, pnicogen, chalcogen, halogen and aerogen bonds, respectively. On the other hand, π-holes also characterized by the positive electrostatic potential are observed for centers in planar molecules or planar fragments of molecules in regions above those planes. π-holes may be attributed to triel centers (13th group of the periodic system). The boron and aluminium trihydrides and trihalides are examples of molecules where triels are characterized by π-holes. The mechanism of the triel bond formation is very similar to the mechanism of the formation of the hydrogen bond. It is the Lewis acid – Lewis base interaction where the electron charge transfer from the base unit to the acid one is observed. Next there is outflow of the electron charge from the triel center to the other parts of the Lewis acid unit; in other words the positive charge of the triel center increases as a result of complexation. The triel bonds are often very strong and often they possess characteristics of typical covalent bonds; this is confirmed by the QTAIM (Quantum Theory of Atoms in Molecules) and NBO (Natural Bond Orbital) approaches. For example, for the triel bonds the bond paths between the triel center and the Lewis base center are observed with the bond critical points (BCPs) attributed to those paths. Similarly for the A-H…B hydrogen bonds the H…B bond paths are observed. The parameters of those BCPs often indicate the covalent character of the triel bonds and analogously those characteristics for H-bonds may also indicate the covalent character of the latter interactions. It is very interesting that the triel bonds are observed experimentally in the real systems; for example in crystal structures. The triel center which is trivalent and possesses the trigonal configuration is hypovalent; it means that the octet rule is not obeyed here because of the valence electrons´ deficiency (the triel center possesses six valence electrons in such species). Thus it may interact with one Lewis base ligand reaching rather stable octet and tetrahedral configuration. If the trivalent triel center interacts with two Lewis base ligands thus it may lead to the configuration of the trigonal bipyramid with the hypervalent and pentavalent triel center. These kinds of the triel species occur in crystal structures that are described here.
Źródło:
Wiadomości Chemiczne; 2017, 71, 7-8; 447-471
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Zastosowanie spektroskopii oscylacyjnej w detekcji barwników azowych w opakowaniach do żywności
Application of vibrational spectroskopy in the detection of azo dyes in food contact packaging materials
Autorzy:
Kucharska, Edyta
Michalski, Jacek
Sąsiadek, Wojciech
Dymińska, Lucyna
Hołubniak, Paulina
Hanuza, Jerzy
Powiązania:
https://bibliotekanauki.pl/articles/27310037.pdf
Data publikacji:
2023
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
azo-dipirydyny
fenylo-azopiridyny
struktura krystaliczna
widma IR i Ramana
drgania normalne wiązań azowych
barwniki azowe w opakowaniach żywności
azo-dipyridines and phenyl-azopyridines
crystal structures
IR and Raman spectra
vibrations of azo bridge
azo dyes in food packing
Opis:
This work is a continuation of our research on spectroscopic and structural properties and applications of a number of azo-dipyridine and phenyl-azopyridine derivatives. In the previous works, the results of DFT quantum calculations were used to discuss infrared and Raman spectra. The presented study generalizes these results using the literature data on the structure of aromatic azo compounds. Analysis of the spectra and detailed assignment of the observed bands to the specific oscillating modes enables their application to identification of azo dyes widely used in the food industry. The bioactivity of azo dyes means that the safety of their use requires the search for new methods of their detection in food. The paper shows that vibrational spectroscopy is an effective diagnostic method for identifying not only the material from which the plastic foil is made, but also the dye used for its dyeing. In this work, the method was applied to colour plastic foils used as pasta packaging. It has been shown that this foil is made of polypropylene, and azo dyes, such as orange yellow (orange dye), tartrazine (yellow dye), allura red (red dye), brilliant blue (blue dye) and a mixture of yellow and blue dyes (green dye) were used for its dyeing.
Źródło:
Wiadomości Chemiczne; 2023, 77, 7-8; 687--718
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-3 z 3

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