Configurational Isomerism in Polyoxovanadates

2018 ◽  
Vol 57 (11) ◽  
pp. 2972-2975 ◽  
Author(s):  
Lisa K. Mahnke ◽  
Aleksandar Kondinski ◽  
Ulrike Warzok ◽  
Christian Näther ◽  
Jan van Leusen ◽  
...  
Keyword(s):  
Configurational Isomerism

scholarly journals A Concise Synthesis of a Methyl Ester 2-Resorcinarene: A Chair-Conformation Macrocycle

2021 ◽  
Author(s):  
Michael R. Reynolds ◽  
Fraser S. Pick ◽  
John Hayward ◽  
John F. Trant
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Methyl Ester ◽  
Chair Conformation ◽  
Selective Recognition ◽  
Aromatic Substitution ◽  
Design And Synthesis ◽  
Hydrogen Bond Strength ◽  
Recognition Elements ◽  
Configurational Isomerism

Anions are important hydrogen bond acceptors in a range of biological, chemical, environmental and medical molecular recognition processes.<sup> </sup>These interactions have been exploited for the design and synthesis of ditopic resorcinarenes as the hydrogen bond strength can be tuned through the modification of the substituent at the 2-position. However, many potentially useful compounds, especially those incorporating electron-withdrawing functionalities, have not been prepared due to the challenge of their synthesis: their incorporation slows resorcinarene formation that is accessed by electrophic aromatic substitution. As part of our broader campaign to employ resorcinarenes as selective recognition elements, we need access to these specialized materials, and in this article we report a straightforward synthetic pathway for obtaining a 2-(carboxymethyl)-resorcinarene, and resorcinarene esters in general. We discuss the unusual conformation it adopts, and propose that this arises from the electron-withdrawing nature of the ester substituents that renders them better hydrogen bond acceptors than the phenols, ensuring that each of those acts as a donor only. DFT calculations show that this conformation arises as a consequence of the unusual configurational isomerism of this compound and interruption of the archetypal hydrogen bonding by the ester functionality.

scholarly journals The rotational and configurational isomerism of N-(monosubstituted ethyl)-amides by nuclear magnetic resonance.

1988 ◽  
Vol 36 (8) ◽  
pp. 2802-2807 ◽  
Author(s):  
JOSE M. AGUIRRE ◽  
ADRIANA F. IBANEZ ◽  
ELBA N. ALESSO ◽  
DORA G. TOMBARI ◽  
GRACIELA Y. MOLTRASIO IGLESIAS
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Configurational Isomerism ◽  
Nuclear Magnetic

Polymorphism and configurational isomerism in 3-(9-anthryl)-1-(3-hydroxyphenyl)prop-2-en-1-one

2019 ◽  
Vol 1195 ◽  
pp. 355-363
Author(s):  
Qi Feng ◽  
Jiali Wang ◽  
Wenhui Huan ◽  
Chao Shen ◽  
Fang Guo ◽  
...  
Keyword(s):  
Configurational Isomerism

Imidazole-containing Bispidine Ligands: Synthesis, Structure and Cu(II) Complexation

2011 ◽  
Vol 66 (7) ◽  
pp. 721-728 ◽  
Author(s):  
Martin Walther ◽  
Madlen Matterna ◽  
Stefanie Juran ◽  
Silke Fähnemann ◽  
Holger Stephan ◽  
...  
Keyword(s):  
Solid State ◽  
Nmr Spectroscopy ◽  
Enol Form ◽  
Trans Configuration ◽  
X Ray Diffraction ◽  
X Ray ◽  
The Impact ◽  
Configurational Isomerism

The preparation and characterization of tris-pyridyl bispidine (3,7-diazabicyclo[3.3.1]nonane) derivatives with benzimidazole and imidazole donor groups at the N-3 position of the bispidine skeleton and their copper(II) complexes are reported. The impact of the hetaryl substituents on the configurational isomerism of piperidones and their corresponding bispidones has been studied by NMR spectroscopy, revealing the exclusive appearance in the enol form for the piperidones in solution and the trans-configuration regarding the two pyridyl substituents, as well as the sole formation of the unsymmetric exo-endo isomers for the corresponding bispidones. Thus, the bispidones are preorganized ligands for building pentacoordinated complexes, confirmed by the preparation and characterization of the corresponding Cu(II) complexes. Of the di-pyridyl piperidones with benzimidazole and imidazole substituents, and of the Cu(II) complex of the benzimidazole-containing bispidone, crystals have become available for the analysis by X-ray diffraction, showing that the piperidones form the enol tautomers also in the solid state.

N-vinylation and N-allylation of 3,5-disubstituted pyrazoles by N–H insertion of vinylcarbenoids

2015 ◽  
Vol 70 (10) ◽  
pp. 747-756 ◽  
Author(s):  
Agagia Gill ◽  
Udo R. Werz ◽  
Gerhard Maas
Keyword(s):  
Double Bond ◽  
Configurational Isomerism

AbstractA vinylcarbenoid approach toward N-functionalization of NH-pyrazoles is presented. The rhodium(II)-catalyzed reaction of methyl styryl-diazoacetate (1) or dimethyl 2-diazoglutaconate (3) with 3,5-disubstituted pyrazoles gave products of carbenoid N–H insertion in high combined yields, although regioselectivity issues posed by the pyrazole or the vinylcarbenoid moiety as well as positional and configurational isomerism concerning the C,C double bond of the latter led to product mixtures. The ambident reactivity of the vinylcarbenoid derived from 1 could be steered by the catalyst: while Rh2(OAc)4 yielded products of direct carbenoid insertion preferentially, silver(I) catalysis strongly favored reaction at the vinylogous site of the carbenoid resulting in an N-allylation of the pyrazoles.

Keto-Enol-Tautomerism and Configurational Isomerism of 2,6-Disubstituted 4-Piperidone-3,5-dicarboxylates

1991 ◽  
Vol 46 (9) ◽  
pp. 1237-1250 ◽  
Author(s):  
Ulrike Holzgrabe ◽  
Willy Friedrichsen ◽  
Karl-F. Hesse
Keyword(s):  
Hydrogen Bond ◽  
Alkyl Group ◽  
Semiempirical Calculations ◽  
Axial Position ◽  
Strong Hydrogen Bond ◽  
Spectroscopic Methods ◽  
X Ray ◽  
Characteristic Values ◽  
Configurational Isomerism

The dialkyl 2,6-dialkylsubstituted 4-piperidone-3,5-dicarboxylates were synthesized by a Mannich procedure. Depending on the substitution at the nitrogen keto-enol-tautomerism and a configurational isomerism at C 2 is observed. The structure of the N-substituted piperidone 24 E (C18H29NO5) has been determined by X-ray analysis: it is characterized by an enol structure of the β-ketoester and an axial position of the alkyl group at C 2 and an equatorial one of the alkyl group at C 6. The O–H···O hydrogen bond shows characteristic values of a strong hydrogen bond. The N-unsubstituted piperidones adopt a ketone structure with the allequatorial position of all substituents. This stereochemistry is confirmed for other enolic and ketone analogues by NMR spectroscopic methods. To work out the reason for the different thermodynamic stabilities of the different stereochemical structures of N-substituted and N-unsubstituted piperidones, various semiempirical calculations were done for series of simple pairs of carbonyl/enol tautomers, substituted acetoacetates, oxoglutarate as well as of systematically varied substituted cyclohexanone, 4-oxacyclohexanone and 4-piperidone derivatives.

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