Search results for "Isomerization"
showing 10 items of 281 documents
Conformational preferences and synthesis of isomers Z and E of oxazole-dehydrophenylalanine
2016
Dehydrophenylalanine, ΔPhe, is the most commonly studied α,β-dehydroamino acid. In nature, further modifications of the α,β-dehydroamino acids were found, for example, replacement of the C-terminal amide group by oxazole ring. The conformational properties of oxazole-dehydrophenylalanine residue (ΔPhe-Ozl), both isomers Z and E, were investigated. To determine all possible conformations, theoretical calculations were performed using Ac-(Z/E)-ΔPhe-Ozl(4-Me) model compounds at M06-2X/6-31++G(d,p) level of theory. Ac-(Z/E)-ΔPhe-Ozl-4-COOEt compounds were synthesized and the conformational preferences of each isomer, Z and E, were investigated using FTIR and NMR-NOE in solutions of increasing p…
Reaction mechanism of regioisomerization in binuclear (diaminocarbene)PdII complexes
2021
Abstract A series of binuclear PdII carbene complexes were synthesized via the treatment of cis-[PdCl2(CNXyl)2] (1) with benzo-1,3-thiazol-2-amines (2–6) and structurally characterized. In every case the reaction leads to the mixture of two regioisomers, which are able to interconvert. The study of the regioisomerization of the binuclear diaminocarbene species showed that it is a first-order reaction, that is, it occurs intramolecularly, and was analyzed with the Hammett function. Electron-withdrawing substituents in the benzothiazole moiety of the complexes as well as increasing the solvent polarity accelerate the reaction. The solvent donor strength correlates less well with the isomeriza…
Theoretical study of the mechanism of branching rearrangement of carbenium ions
1996
Abstract Owing to the practical interest of the acid catalyzed isomerization reactions of hydrocarbons, the mechanism of the branching rearrangements of C 4 H 9 + and C 5 H 11 + carbenium ions has been studied theoretically using ab initio methods which include electron correlation and extended basis sets. It has been found that the protonated cyclopropane-type species does not appear as a common intermediate for these reactions, since it is a transition state and not a minimum on the potential energy surfaces studied. In the case of C 4 H 9 + cation, the protonated methyl-cyclopropane ring is the transition state for the carbon scrambling reaction in the secondary n-butyl cation, while the…
Gelation of smectic liquid crystal phases with photosensitive gel forming agents.
2020
This paper studies the potential of 3 newly synthesized low molecular weight gelling agents (2 of them with azo groups) with the semicarbazide group as a H-bonding motif to gel the smectic phase of a commercial chiral smectic C material. To detect gelation two methods were used: the stabilization of the director pattern, which measures the interaction of the physical gel network with the LC-director, and the suppression of the onset of electrohydrodynamic instabilities, which measures the increase of viscosity. Special emphasis was put on the influence of the photochemical - isomerization of the gelling agents on gelation.From the stabilization of the director pattern an elastic component c…
Studio teorico della reazione di idroisomerizzazione del cis-butene su cluster di palladio supportato
2008
TiO2-induced photoisomerization of caffeic acid
2014
Non-degenerate 1,2-silyl shift in silyl substituted alkyltrimethylcyclopentadienes
2005
Abstract The five new silanes C5Me3RSiMenCl3 − n (n = 3, R = i-Pr (5); n = 2, R = i-Pr (6); n = 2, R = s-Bu (7); n = 2, R = cyclohexyl (8); and n = 3, R = t-Bu (9)) were synthesized by reaction of 1-alkyl-2,3,4-trimethylcyclopentadienyl lithium salts with appropriate chlorosilane and characterized by NMR, MS, and IR spectra. At elevated temperatures (250–360 K), all the silanes undergo a non-degenerate sigmatropic silyl rearrangement, which generates non-equivalent structures a and b. The presence of minor structure c was observed in compounds 5 and 7 only. The Diels–Alder cycloaddition of 5 with strong dienophiles tetracyanoethylene (TCNE), and dimethylacetylenedicarboxylate (DMAD) provide…
Photoinduced effects on the magnetic properties of the (Fe0.2Cr0.8)1.5[Cr(CN)6] Prussian blue analogue
2019
International audience; One of the most attractive characteristics of some Prussian blue derivatives is the sensitivity of their magnetic properties to the irradiation with light. In this work photoinduced effects in the (Fe0.2Cr0.8)1.5[Cr(CN)6]·15H2O PBA have been studied by means of X-ray-based spectroscopies and magnetometry. It is found that the photosensitivity of this compound is mostly centred on the Fe cations: the exposure to green light induces a transfer of electrons from them to the Cr that provokes a reversal of the previously existing linkage isomerization and increases the elastic strain caused by the misfit of the unit cells of the Fe–NC–Cr and Cr–NC–Cr sublattices. The gree…
Syntheses of Four Enantiomers of 2,3-Diendo- and 3-Endo-aminobicyclo[2.2.2]oct-5-ene-2-exo-carboxylic Acid and Their Saturated Analogues
2013
Abstract: Ethyl 2,3- diendo -3-aminobicyclo[2.2.2]oct- 5-ene-2-carboxylate ((±)- 1 ) was resolved with O , O '-dibenzoyltartaric acid via diastere omeric salt formation. The efficient synthesis of the enantiomers of 2,3- diendo -3-aminobicyclo[2.2.2]oct- 5-ene-2-carboxylic acid ((+)- 7 and (–)- 7 ), 3- endo -aminobicyclo[2.2.2]oct-5-ene-2- exo -carboxylic acid ((+)- 5 and (–)- 5 ), cis - and trans -3-aminobicyclo[2.2.2]octa ne-2-carboxylic acid ((+)- 6 , (–)- 6 , (+)- 8 and (–)- 8 ) was achieved via isomerization, hydrogenation and hydrolysis of the corresponding esters (–)- 1 and (+)- 1 . The stereochemistry and relative configurations of the synthesized compounds were determined by NMR sp…
Introduction of unsaturated segments in the bridge of metacyclophanes
1995
Abstract The cyclophanes 2a,b, which contain a triple bond in the meta-bridge, were transformed to the allenes 3a,b by the action of bases or acids. A further isomerization yielded the dienes 4a,b with ( E,Z )- or ( Z,Z )-configuration.