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Wyświetlanie 1-15 z 15
Tytuł:
Kompleksy metali dużych makrocykli iminowych i aminowych
Metal complexes of large imine and amine macrocycles
Autorzy:
Lisowski, Jerzy
Powiązania:
https://bibliotekanauki.pl/articles/1410886.pdf
Data publikacji:
2021
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
makrocykle
chiralność
kompleksy wielordzeniowe
lantanowce
macrocycles
chirality
polynuclar complexes
lanthanides
Opis:
Macrocyclic complexes continue to attract considerable attention due to their significance in biological systems, catalysis, medical diagnostics and other fields. While the most intensively studied macrocycles containing donor nitrogen atoms are tetraazamacrocycles such as porphyrins or cyclen derivatives, larger macrocyclic ligands containing up to 18 (or even more) donor atoms are also known. Due to their enlarged size, these macrocycles can bind large metal ions such as lanthanide(III) ions or bind multiple metal ions. In this review a subclass of large macrocycles will be discussed i.e. macrocyclic amines and imines that can be generated in the condensation of diamines with dicarbonyl compounds, in particular with 2,6-diformylpyridine or 2,6-diformylphenols. These macrocycles of various sizes lead to a rich variety of structures of metal complexes, including polynuclear complexes. Moreover, macrocycles derived from enantiopure trans-1,2- diaminocylohexane form chiral metal complexes that exhibit unusual effects such as helicity inversion, enantioselective self-recognition or enantiodiscrimination of organic guest molecules.
Źródło:
Wiadomości Chemiczne; 2021, 75, 5-6; 603-629
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Influence of chirality on two-dimensional deformations in twisted flexoelectric nematic layers
Wpływ chiralności na dwuwymiarowe odkształcenia warstw nematyków fleksoelektrycznych
Autorzy:
Buczkowska, Mariola
Powiązania:
https://bibliotekanauki.pl/articles/952822.pdf
Data publikacji:
2019
Wydawca:
Politechnika Łódzka. Wydawnictwo Politechniki Łódzkiej
Tematy:
twisted nematic
flexoelectricity
chirality
periodic patterns
nematyki skręcone
fleksoelektryczność
chiralność
wzory periodyczne
Opis:
Two-dimensional deformations induced by electric field in twisted nematic cells filled with liquid crystal possessing flexoelectric properties were simulated numerically. The influence of chiral dopants on the occurrence and structure of the spatially periodic patterns was investigated. It was found that the chirality influences mainly the direction of the periodic patterns whereas the threshold voltage for deformation and the width of the stripes are weakly affected
Dwuwymiarowe deformacje indukowane polem elektrycznym w warstwach ciekłych kryształów nematycznych posiadających właściwości fleksoelektryczne były symulowane numerycznie. Zbadano wpływ chiralnych domieszek na strukturę tych odkształceń i ich rozwój pod wpływem pola elektrycznego. Stwierdzono, że chiralność wpływa głównie na kierunek odkształceń, podczas gdy napięcie progowe na odkształcenie i przestrzenny okres odkształceń słabo zależą od chiralności nematyka. Stwierdzono, że chiralność wpływa głównie na kierunek odkształceń, podczas gdy jej wpływ na napięcie progowe i na przestrzenny okres odkształceń jest nieznaczny.
Źródło:
Scientific Bulletin. Physics / Technical University of Łódź; 2019, 40; 5-12
1505-1013
2449-982X
Pojawia się w:
Scientific Bulletin. Physics / Technical University of Łódź
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Proces samo-dysproporcjowania enancjomerów podczas chromatografii kolumnowej
Self-disproportionation of enantiomers via column chromatography
Autorzy:
Wzorek, Alicja
Kwiatkowska, Magdalena
Urbaniak, Mariusz
Gawdzik, Barbara
Powiązania:
https://bibliotekanauki.pl/articles/27310046.pdf
Data publikacji:
2023
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
chiralność
chromatografia
asocjacja
enancjomeryczne wzbogacanie
oddziaływania międzycząsteczkowe
chirality
chromatography
association
enantiomeric enrichment
intermolecular interactions
Opis:
The review is devoted to self-disproportionation of enantiomers (SDE) phenomenon which has been observed for many different classes of chiral organic compounds. The SDE phenomenon occurs when the fractionation of an enantioenriched sample due the application of a physicochemical process under achiral conditions results in the variation of the proportion of the enantiomers present across the fractions, though the overall composition in terms of the sample ee remains unchanged. The SDE process can be considered in terms of separating the excess enantiomer from the racemate. The basic terminology related to SDE was described. The formation of the SDE under chromatographic conditions is the result of an association process occurring in a solution of a chiral, non-racemic compound. Information on preferred interactions leading to homo-/heterochiral supramolecules can be provided by quantum chemical calculations, NMR spectroscopy and comparison of crystal structures of the racemic and enantiomeric crystals. Several examples of the chromatographic experiments with different classes of compounds were given in two purposes 1) to highlight the possibility of application SDE during column chromatography as the method for enantiopurification of the chiral, non-racemic compounds; 2) to demonstrate that a standard workup (chromatographic purification, evaporation) can alter the stereochemical outcome of asymmetric reactions.
Źródło:
Wiadomości Chemiczne; 2023, 77, 5-6; 425--448
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Chiralne amidki litu : właściwości i wybrane zastosowania syntetyczne
Chiral lithium amides : properties and selected synthetic applications
Autorzy:
Piwońska, Magdalena
Powiązania:
https://bibliotekanauki.pl/articles/1409982.pdf
Data publikacji:
2021
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
chiralność
synteza stereoselektywna
enolan
indukcja asymetryczna
lit
chirality
stereoselective synthesis
enolate
asymmetric induction
lithium
Opis:
Reactions involving carbonyl groups are one of the most important transformations in organic chemistry. The nucleophilic properties of carbonyl compounds, when they are in the form of enolate ions, offer many possibilities for creating new carbon-carbon bonds in reactions with electrophiles. In the case of cyclic ketones, enolate formation can be stereocontrolled by deprotonation with the use of chiral lithium amides. Stereoselective formation of the chiral lithium enolate determines the stereochemistry of the product of the subsequent reaction with the electrophile. The induction of chirality in the reaction of enolate ions with electrophiles can also be achieved by using metals other than lithium, i.e. magnesium. When other alkali metals are used, an organometallic catalyst containing a chiral ligand must be present in the reaction. The presence of particular structural elements allow distinguishing the chiral lithium amides between eight major classes. Due to the high reactivity of lithium enolates, they are often converted into the silyl enol ether. This is done in two ways: internal quench (in situ reaction with TMSCl) or external quench. Due to aggregation of the chiral lithium amides and, thus, a decrease in asymmetric induction, the addition of LiCl is necessary for reactions run in external quench conditions. Although there are known examples of the use of chiral lithium amides in a catalytic amount in the deprotonation of epoxides, there is only one example of using less than stoichiometric amounts of chiral lithium amides in the deprotonation of ketones. There are many reports in the literature on the use of chiral lithium amides in total syntheses. The chiral lithium amides were used to form chiral enol silyl ether intermediates, e.g. in synthesis of chlortetaine or (+)-ibogamine. They are also used to form chiral lithium enolates which reacts directly with electrophiles, e.g. in synthesis of lasonolide A.
Źródło:
Wiadomości Chemiczne; 2021, 75, 5-6; 771-798
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Trans-1,2-diaminocykloheksan – niezwykła kariera outsidera
Trans-1,2-diaminocyclohexane – unprecedented outsider’s career
Autorzy:
Petryk, M.
Kwit, M.
Powiązania:
https://bibliotekanauki.pl/articles/171507.pdf
Data publikacji:
2013
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
struktura
chiralność
konformacja
synteza asymetryczna
rozpoznanie molekularne
structure
chirality
conformation
asymmetric synthesis
molecular recognition
Opis:
An enantiopure trans-1,2-diaminocyclohexane is one of the most widely used chiral diamines in modern organic chemistry. This chiral building block, readily available from waste industrial products, emerges as a major figure in the field of asymmetric synthesis. The unique structural and conformational properties of trans-1,2-diaminocyclohexane make it very useful for the development of new synthetic strategies, taking advantage of its geometrical pre-organization. In this short article, we will highlight the utility of enantiomerically pure trans-1,2-diaminocyclohexane derivatives as broad-range chiral reagents and ligands for catalytic cycles. A brief overview of the aspects of applications in the field of molecular recognition will also be given.
Źródło:
Wiadomości Chemiczne; 2013, 67, 5-6; 393-442
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Asymetryczna aminokataliza : użyteczne narzędzie w tworzeniu chemicznej różnorodności
Asymmetric aminocatalysis : a useful tool providing access to chemical diversity
Autorzy:
Skrzyńska, Anna
Przydacz, Artur
Dyguda, Mateusz
Topolska, Aleksandra
Albrecht, Łukasz
Powiązania:
https://bibliotekanauki.pl/articles/171692.pdf
Data publikacji:
2020
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
synteza asymetryczna
aminokataliza
chiralność
indukcja asymetrii
związki heterocykliczne
asymmetric synthesis
aminocatalysis
chirality
asymmetric induction
heterocyclic compounds
Opis:
Over the last 20 years asymmetric aminocatalysis has emerged as highly useful and reliable method of asymmetric synthesis. It involves the use of primary or secondary amines as catalysts of various stereoselective transformations of carbonyl substrates. Owing to the diverse activation strategies available in asymmetric aminocatalysis, it became a method of choice when the functionalization of prochiral aldehydes and ketones is considered. As a consequence, a direct and straightforward access to various chiral building blocks is possible that is of relevance to modern stereocontrolled organic synthesis. In the manuscript, the development of various aminocatalytic activation concepts is described and recent, selected contributions to this field of chemistry discussed. Main advantages of these strategies are highlighted providing an overview of this fascinating area of research.
Źródło:
Wiadomości Chemiczne; 2020, 74, 3-4; 255-284
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Eksperymentalne i teoretyczne oznaczanie konfiguracji absolutnej związków chiralnych metodami chiralooptycznymi
Experimental and theoretical determination of the absolute configuration of chiral molecules by chiroptical methods
Autorzy:
Kwit, M.
Powiązania:
https://bibliotekanauki.pl/articles/171859.pdf
Data publikacji:
2011
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
struktura
chiralność
aktywność optyczna
dichroizm kołowy
skręcalność optyczna
structure
chirality
optical activity
circular dichroism
optical rotation
Opis:
Chirality is of paramount importance in chemistry and life sciences. Electronic circular dichroism (ECD) as well as optical rotation (OR) are fundamental properties of chiral molecules. These chiroptical properties provide rich information about conformation and configuration of the molecules. Although empirical correlations between chiroptical phenomena, mostly ECD, and molecular stereochemistry have existed for some time, the development of new accurate theoretical methods opened new opportunities for correlation of chiroptical properties with structure. Computational chemistry has made an amazing progress during the past two decades, moving this highly specialized discipline into the mainstream, and making a renaissance in chiroptical methods. This short review is meant as an introduction to the modern approach to optical activity of chiral molecules. Some illustrative applications will put the emphasis on practical applications of the theoretical/experimental analysis of complex molecules including highly flexible bistramide C and noncovalently bonded donor-acceptor dyad. The importance of the solvent effect is briefly discussed and a typical methodology is described and its strengths and weak points are commented.
Źródło:
Wiadomości Chemiczne; 2011, 65, 1-2; 33-58
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Asymetryczne reakcje pericykliczne katalizowane kompleksami magnezu
Magnesium-catalyzed asymmetric pericyclic reactions
Autorzy:
Czombik, Anna
Powiązania:
https://bibliotekanauki.pl/articles/2200433.pdf
Data publikacji:
2022
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
chiralność
kataliza asymetryczna
reakcja pericykliczna
kwas Lewisa
magnez
chirality
asymmetric catalysis
pericyclic reactions
Lewis acid
magnesium
Opis:
II Group-metals, like magnesium, are one of the most widespread elements in the environment. The abundance of II-group metals in the Earth’s crust is over 108 times greater than the precious metals. For the industrial applications, the important factors are the low costs of production and higher accessibility of their compounds. This puts the spotlight on alkaline-earth metals competing with transition elements as catalysts in organic synthesis. Features of their derivatives, like mild Lewis acidity and strong Brønsted basicity enabled them to catalyze reactions where Lewis-acidactivation of the substrate is essential. In this review the emphasis was put on magnesium-catalyzed pericyclic reactions, which are recognized as one of the most important methods of new carbon-carbon or carbon-heteroatom bonds formation. Using the catalysts based on II-group metal cations and chiral ligands, a highly stereoselective conversion of achiral substrates into enantioenriched products is possible. The Mg-based catalysts have been used in Diels-Alder, ene and 1,3-dipolar additions. Described synthesis methods were characterized by high efficiency (chemical yields and enantiomeric excesses). Where applicable, the relationships between the structure of catalyst/substrates, conditions and efficiency were discussed. Just now there are a few applications, for example in synthesis of alkaloid (–)-manzacidine or antibiotic of algal origin – (–)-malyngolide.
Źródło:
Wiadomości Chemiczne; 2022, 76, 9-10; 755--788
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Upper upper Albian (Mortoniceras rostratum Zone) cephalopods from Clansayes (Drôme, south-eastern France)
Autorzy:
Jattiot, Romain
Lehmann, Jens
Latutrie, Benjamin
Tajika, Amane
Vennin, Emmanuelle
Vuarin, Pauline
Brayard, Arnaud
Fara, Emmanuel
Trincal, Vincent
Powiązania:
https://bibliotekanauki.pl/articles/2086664.pdf
Data publikacji:
2022
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
ammonites
Cretaceous
upper Albian
taxonomy
south-eastern France
shell chirality
amonity
kreda
alb
taksonomia
Francja południowo-wschodnia
chiralność
Opis:
We document an upper upper Albian (Mortoniceras rostratum Zone) cephalopod assemblage from Clansayes (Drôme, south-eastern France). Although fossils are rare in local exposures and in the single sampled level, a decade of intensive fossil collecting yielded 290 ammonite and 5 nautilid specimens. In total, we describe 1 species of nautilid and 24 species (within 17 genera) of ammonites, including 13 heteromorphs. Only two of these ammonite taxa were previously recorded from the upper upper Albian at Clansayes, which demonstrates the value of this fauna with regard to taxonomy, palaeobiology and palaeobiogeography. Based on morphological and biometric analyses performed on an extensive material (104 specimens), we discriminate two species for the heteromorphic ammonite genus Mariella Nowak, 1916 within the Mortoniceras rostratum Zone. In addition, we investigate shell chirality patterns in Mariella from the late Albian of southern France. Upon comparison of the Clansayes material with older material from the immediately underlying upper Albian Mortoniceras fallax Zone at the neighbouring Salazac locality, we identify an increase in the proportion of sinistral specimens. This observed increase in the frequency of sinistral Mariella specimens may hypothetically be part of a global evolutionary pattern, considering that nearly all documented younger Cenomanian Mariella (and more generally Cenomanian turrilitids) are sinistral.
Źródło:
Acta Geologica Polonica; 2022, 72, 2; 187--233
0001-5709
Pojawia się w:
Acta Geologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Alkaloidy kory chinowej : małe cząsteczki, które wiele mogą
Cinchona alkaloids : small hardworkers
Autorzy:
Kacprzak, K.
Czarnecki, P.
Powiązania:
https://bibliotekanauki.pl/articles/172207.pdf
Data publikacji:
2013
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
chinina
alkaloidy kory chinowej
chinidyna
synteza asymetryczna
rozdział enancjomerów
chiralność
quinine
cinchona alkaloids
quinidine
asymmetric synthesis
enantiomer separation
chirality
Opis:
Cinchona alkaloids comprising quinine, quinidine, cinchonidine and cinchonine as the major members constitute a unique class of quinoline alkaloids with tremendous impact on human civilization (Section 1). The odyssey of Cinchona alkaloids began with the discovery of their antimalarial properties followed by antiarrhytmic action of quinidine. Currently medicinal chemistry of Cinchona alkaloids derivatives develops rapidly and many other activities such as cytotoxic, multidrug resistance inhibitory have been demonstrated (Section 5) [5]. Beside medicine Cinchona alkaloids gave also the fundaments of stereochemistry and asymmetric synthesis. An extraordinary catalytic potency of parent and modified Cinchona alkaloids (deserving privileged catalyst classification) include more than 50 types of diverse stereoselective reactions, with few spectacular such as asymmetric dihydroxylation of alkenes or heterogeneous α-ketoesters hydrogenation (Section 3) [3]. Last but not least the portfolio of applications of Cinchona alkaloids includes resolution of racemates by diastereomeric crystallization or by the use of Cinchona- -based chiral stationary phases for ion-exchange enantioselective chromatography and other recognition or sensing systems (Section 4) [166]. Easy transformation of Cinchona alkaloids (for example by click chemistry) into other chiral and modular building blocks together with current pressure on a more intense exploration of sustainable products make cinchona alkaloids of primary importance for modern synthetic, catalytic and medicinal chemistry. The aim of this review which covers over 200 references is to briefly summarize all aspects of Cinchona alkaloid chemistry and biology with the special emphasis on new applications.
Źródło:
Wiadomości Chemiczne; 2013, 67, 5-6; 443-493
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Chromatograficzny rozdzial enancjomerow w analizie zywnosci i produktow naturalnych
Autorzy:
Bojarski, J
Powiązania:
https://bibliotekanauki.pl/articles/828350.pdf
Data publikacji:
2000
Wydawca:
Polskie Towarzystwo Technologów Żywności
Tematy:
analiza zywnosci
enancjomery
zywnosc
chiralnosc
zwiazki zapachowe
zwiazki smakowe
produkty spozywcze
food analysis
enantiomer
food
chirality
flavour compound
aroma compound
food product
Opis:
W artykule podano podstawowe definicje chiralności oraz metodykę chromatograficznego rozdziału oznaczania enancjomerów w produktach żywnościowych i naturalnych. Zaprezentowano także odpowiednie przykłady oznaczania antypodów optycznych aminokwasów oraz związków zapachowych smakowych, zaczerpnięte z literatury.
Basic definitions of chirality and methods of chromatographic separation and determination of enantiomers in food and natural products have been discussed. Appropriate examples of such analyses taken from the literature for optical antipodes of amino acids and aroma and flavor compounds have been presented.
Źródło:
Żywność Nauka Technologia Jakość; 2000, 07, 2; 120-127
1425-6959
Pojawia się w:
Żywność Nauka Technologia Jakość
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Hiperwalentne związki siarki, selenu i telluru. Część 2. Sulfurany 10-S-3 i 10-S-4
Hypervalent compounds of sulfur, selenium and tellurium. Part 2. Sulfuranes 10-S-3 and 10-S-4
Autorzy:
Zając, A.
Powiązania:
https://bibliotekanauki.pl/articles/172591.pdf
Data publikacji:
2012
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
hiperwalentność
wiązanie 3c-4e
sulfuran
pseudorotacja Berry'ego
bipiramida trygonalna
synteza
chiralność
aktywność optyczna
izomeryzacja
sprzęganie ligandów
wymiana liganda
hypervalency
3c-4e bond
sulfurane
Berry pseudorotation
trigonal bipyramid
synthesis
chirality
optical activity
isomerization
ligand coupling
ligand exchange
Opis:
The compounds presented herein are sulfuranes 10-S-3 and 10-S-4 containing hypervalent sulfur atom. They have been known for a relatively long time. Nevertheless, they, and especially 10-S-4 species, are still of great interest due to their unique properties. The review presents recent approaches to the synthesis of these compounds, their selected structural, physical, chemical, stereochemical and electronic properties and their use as reagents and catalysts in several reaction types. The presence of structures of these types as intermediates, which explains selected reaction mechanisms, will also be shown.
Źródło:
Wiadomości Chemiczne; 2012, 66, 7-8; 593-622
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Hiperwalentne związki siarki, selenu i telluru. Część 4. Selenurany i tellurany
Hypervalent compounds of sulfur, selenium and tellurium. Part 4. Selenuranes and telluranes
Autorzy:
Zając, A.
Powiązania:
https://bibliotekanauki.pl/articles/171678.pdf
Data publikacji:
2012
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
hiperwalentność
wiązanie 3c-4e
selenuran
perselenuran
telluran
pertelluran
bipiramida trygonalna
bipiramida tetragonalna
synteza
chiralność
aktywność optyczna
izomeryzacja
inwersja klinowa
hypervalency
3c-4e bond
selenurane
perselenurane
tellurane
pertellurane
trigonal bipyramid
tetragonal bipyramid
synthesis
chirality
optical activity
isomerization
cuneal inversion
Opis:
In this part selenuranes (10-Se-4 and 10-Se-5) and perselenuranes 12-Se-6 as well as telluranes 10-Te-4 and pertelluranes 12-Te-6 will be presented. The main goal is to describe recent reports on the synthesis, chemical, physical, spectral and conformational behavior, stereochemistry, stability and biological activity of these compounds. Their occurrence as reaction intermediates will also be shown.
Źródło:
Wiadomości Chemiczne; 2012, 66, 11-12; 1119-1144
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Hiperwalentne związki siarki , selenu i telluru. Część 3. Sulfuran Martina , sulfurany 10-S-5 i 12-S-6
Hypervalent compounds of sulfur, selenium and tellurium. Part 3. Martin su lfurane , sulfuranes 10-S-5 and 12-S-6
Autorzy:
Zając, A.
Powiązania:
https://bibliotekanauki.pl/articles/171640.pdf
Data publikacji:
2012
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
hiperwalentność
wiązanie 3c-4e
sulfuran
persulfuran
sulfuran Martina
bipiramida trygonalna
bipiramida tetragonalna
synteza
chiralność
aktywność optyczna
izomeryzacja
sprzęganie ligandów
hypervalency
3c-4e bond
sulfurane
persulfurane
Martin sulfurane
trigonal bipyramid
tetragonal bipyramid
synthesis
chirality
optical activity
isomerization
ligand coupling
Opis:
In this part of the review one of the most famous 10-S-4 sulfurane called Martin sulfurane together with sulfuranes 10-S-5 and persulfuranes 12-S-6 will be presented. Martin sulfurane has been well known for a relatively long time but it is still useful in organic synthesis as a dehydrating, coupling and oxidizing agent. Its use in selected substitution reactions will be also described. Next, synthesis and selected properties of sulfuranes 10-S-5, mainly sulfurane oxides, and persulfuranes 12-S-6, will be shown. Besides synthetic methods, the review is focused on the investigations of the stability and isomerization of these types of compounds, which is particularly interesting for persulfuranes, because of the presence of three 3c-4e bonds.
Źródło:
Wiadomości Chemiczne; 2012, 66, 9-10; 893-907
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Hiperwalentne związki siarki, selenu i telluru. Część 1. Charakterystyka ogólna
Hypervalent compounds of sulfur, selenium and tellurium. Part 1. General characteristics
Autorzy:
Zając, A.
Powiązania:
https://bibliotekanauki.pl/articles/172599.pdf
Data publikacji:
2012
Wydawca:
Polskie Towarzystwo Chemiczne
Tematy:
hiperwalentność
wiązanie 3c-4e
sulfuran
persulfuran
selenuran
perselenuran
telluran
pertelluran
pseudorotacja Berry'ego
sulfuran Martina
bipiramida trygonalna
bipiramida tetragonalna
synteza
chiralność
aktywność optyczna
izomeryzacja
hypervalency
3c-4e bond
sulfurane
persulfurane
selenurane
perselenurane
tellurane
pertellurane
Berry pseudorotation
Martin sulfurane
trigonal bipyramid
tetragonal bipyramid
synthesis
chirality
optical activity
isomerization
Opis:
The goal of this four-part review is a presentation of the results of recent studies on the properties and chemistry of hypervalent sulfur, selenium and tellurium compounds. The term “hypervalency” has been known since 1969 when Musher used it to describe molecules bearing heteroatoms which formally did not fulfill the octet rule. This violation was explained by the postulate concerning the existence of a 3-center 4-electron bond between a hypervalent heteroatom and two axial electronegative ligands. The bond is the a combination of two ligand orbitals and a pz orbital of a central heteroatom which results in the formation of three molecular orbitals. The distances between the central atom and these two ligands are longer than the length of the typical sp2 bonds, such as equatorial ones. Moreover, the effective electron density is shifted from the central atom towards the axial ligands what results in the fulfillment of the octet rule of this atom. The geometry of this system is trigonal bipyramid (Fig. 2), except from compounds having three 3-center 4-electron (3c-4e) bonds which have tetragonal bipyramid geometry (Fig. 3). The term “geometry” includes positions of ligands and lone electron pairs. The stability of hypervalent compounds is affected by a few factors: electronegativity of ligands, formation of five-membered cyclic structures involving the central atom and the number of electron shells of the central atom. Martin proposed three-symbol notation N-X-L for these structures, which was further modified (Tab. 1). Hypervalent compounds can isomerize according to various mechanisms: Berry pseudorotation (Scheme 1), turnstile rotation (Scheme 2), cuneal inversion (Scheme 3), lever mechanism (Scheme 4), or Bailar twist (Scheme 5). Furthermore, hypervalent structures of 10-X-4 and 10-X-5 type with trigonal bipyramid geometry, C1 or C2 symmetry and at least three different ligands can exist as optically active species (Tab. 2, Fig. 5–7, Scheme 6), especially the "spiro" ones, which are resistant to isomerization. In 1977 Martin and Balthazor proposed extended Cahn-Ingold-Prelog convention for description of the absolute configuration of chiral hypervalent compounds (Fig. 5).
Źródło:
Wiadomości Chemiczne; 2012, 66, 5-6; 529-541
0043-5104
2300-0295
Pojawia się w:
Wiadomości Chemiczne
Dostawca treści:
Biblioteka Nauki
Artykuł
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