Search results for "Isomerization"
showing 10 items of 281 documents
Isomerization and disproportionation of m-xylene in a zeolite with 9- and 10-membered ring pores: Molecular dynamics and catalytic studies
2006
The unique pore topology of zeolite ITQ-13 with 9-membered ring (MR) channels intersected by perpendicular 10-MR channels and larger void space with 10-MR cross-sections was studied for meta-xylene isomerization and disproportionation. Product distribution was interpreted on the basis of pore topology and compared with zeolites with 12-MR (β), 10-MR, and intersecting 12-MR cavities (NU-87), as well as 10-MR (ZSM-5) zeolites. The presence of cavities allows more space for bulky intermediates and/or products and also provides room for molecules to drive consecutive reactions toward thermodynamic equilibrium. Channels, on the other hand, allow diffusion without trapping if their free diameters…
Reversible and Efficient Light-Induced Molecular Switching on an Insulator Surface
2018
Prototypical molecular switches such as azobenzenes exhibit two states, i.e., trans and cis, with different characteristic physical properties. In recent years various derivatives were investigated on metallic surfaces. However, bulk insulators as supporting substrate reveal important advantages since they allow electronic decoupling from the environment, which is key to control the switching properties. Here, we report on the light-induced isomerization of an azobenzene derivative on a bulk insulator surface, in this case calcite (101̅4), studied by atomic force microscopy with submolecular resolution. Surprisingly, cis isomers appear on the surface already directly after preparation, indi…
On the FCNS⇆FC(NS) reaction: A matrix isolation and theoretical study
2015
Abstract The FCNS ⇆ FC(NS) photoisomerization process is a simple model system for molecular switches. Here, we examined the switching processes by experimental and theoretical methods. Prior matrix-isolation IR spectroscopic studies were complemented by matrix-isolation UV spectroscopic measurements to assist the interpretation of the mechanism of the ring closure and opening processes and to verify the accuracy of the computations on the vertical excitation energies. Vertical excitation energies were computed by the EOMEE-CCSD, MCSCF, and MR-CISD methods. Conical intersections were also searched for and three conical intersections along the reaction path FCNS → FC(NS) were located, one co…
Gold nanoparticle catalysis of the cis-trans isomerization of azobenzene
2013
Ablated, “pseudo-naked” gold nanoparticles (AuNPs) catalyze the cis–trans isomerization of substituted azobenzenes. para-Substitution was found to affect the rate of isomerization, suggesting the participation of AuNP-mediated electron transfer in the isomerization mechanism. Fil: Hallet Tapley, Geniece. University of Ottawa; Canadá Fil: D'Alfonso, Claudio. University of Ottawa; Canadá. Universita Di Roma; Italia Fil: Pacioni, Natalia Lorena. University of Ottawa; Canadá Fil: McTiernan, Cristopher D.. University of Ottawa; Canadá Fil: Gonzalez Bejar, Maria. University of Ottawa; Canadá. Universidad de Valencia; España Fil: Lanzalunga, Osvaldo. Universita Di Roma; Italia Fil: Alarcon, Emilio…
Triazolopyridines. Part 28. The ring–chain isomerization strategy: triazolopyridine- and triazoloquinoline–pyridine based fluorescence ligands
2012
Abstract The ring–chain isomerization of [1,2,3]triazolo[1,5-a]pyridines or [1,2,3]triazolo[1,5-a] quinolines has been efficiently employed as a tool to provide tridentate fluorescent structures. Based on these scaffolds, a new family of highly fluorescent compounds has been synthesized and evaluated for the recognition of zinc or copper cations. In addition, the 1:1 Zn+2-L complex of a naphthalene triazolopyridine–pyridine derivative revealed high efficiency as sensor for anions providing large binding constants for nitrite and cyanide.
Synthesis of Enantiopure ω-(4-Fluorophenyl)-6,11-Methylene Lipoxin B4 Methyl Ester
2021
AbstractThe synthesis of Lipoxin B4 analogues (LXB4) to gain access to stabilized inflammation-resolving compounds is an active field of research. Focusing on variation and stabilization of the conjugated E,Z,E,E C6–C13 tetraene moiety of natural LXB4, a methylene bridge introduced between C6 and C11 suppresses any Z/E isomerization of the C8–C9 olefin. Furthermore, rapid ω-oxidation (C20) should be avoided by replacing the C18–C20 segment by an aromatic moiety. Optically active C1–C12 building blocks were accessed from methyl cycloheptatriene-1-carboxylate (C6–C11, C21) and glutaryl chloride (C1–C5) as described earlier. The ω-segment was generated via a five-step sequence starting from 4-…
Role of the gem-Difluoro Moiety in the Tandem Ring-Closing Metathesis−Olefin Isomerization: Regioselective Preparation of Unsaturated Lactams
2006
Careful selection of the metathesis catalyst, solvent, and reaction conditions allows for the efficient and regioselective synthesis of isomeric fluorinated and nonfluorinated lactam derivatives II and III from precursor amides I through a ring-closing metathesis (RCM) reaction or a tandem RCM-isomerization protocol, respectively. The presence of the gem-difluoro moiety in the starting materials exerts a pivotal effect by directing the isomerization step, making the overall tandem transformation a regioselective process. The scope, limitations, and synthetic usefulness of this protocol are also discussed.
Versuche zur Herstellung linolsäurearmen Ölsäureesters mit Rhodium‐Zinn‐Komplexen als Katalysatoren
1978
Der Linolsauremethylester last sich in Gegenwart eines hohen Uberschusses an Olsaureester mit Rhodiumkomplexen und metallorganischen Zinnverbindungen als Katalysatoren selektiv oligomerisieren. Die Isomerisierung des Olsaureesters kann uber die Wahl einer geeigneten Zinnverbindung inhibiert werden. The Preparation of Oleic Acid Ester with Reduced Linoleic Acid Content by Use of Rhodium-Tin Complexes as Catalysts The linoleic acid methylester can be oligomerized selectively in the presence of a high excess of oleic acid ester with rhodium complexes and metalorganic tin compounds as catalyst. The isomerisation of the oleic acid ester can be inhibited by the choice of a suitable tin compound.
Hybrid magnetic materials based on layered double hydroxides: from the chemistry towards the applications
2014
Layered double hydroxides (LDHs) are the leitmotiv of this dissertation. Contradicting the assertion that “any past was better”, LDHs have been continuously revisited from the middle of the twentieth century, and represent an excellent example of the never-ending beauty of Chemistry. New synthetic perspectives are giving a new impetus to LDH chemistry, which among hybrid materials, are finding their heyday. This is resulting in novel materials and also paving the way for new fundamental and practical insights. This dissertation is focused on magnetic LDHs, and for the sake of clarity it is organized in three main parts: we will move from basic synthetic and physical aspects of LDHs, through…
From Pentalene to Dicyclopenta[b,g]naphthalene, or the Change towards Delocalized Structures
2005
Lining triples-corrected coupled-cluster methods as well as other high-level theoretical approximations, the optimized parameters and isomerization barriers of the family of compounds cyclopentadiene-(benzene) x -cyclopentadiene (x 0, 1, 2) are computed. In contrast to previous studies, s-indacene presents a localized C 2 h geometry. Also, the localized structure of pentalene is found to be the most stable, but when two benzene rings are intercalated between the five-member rings of pentalene, the resulting molecule preferably adopts a delocalized D 2 h conformation.