Search results for "Isomerization"

Preparation and Photochemistry of Dendrimers with Isolated Stilbene Chromophores

2005

In addition to the model compounds 4a and 4b, the dendrimers 11 and 14 with trans-stilbene chromophores in the core and on the periphery of the dendrons were prepared and their photochemistry was studied in solution and in neat films. Due to the flexibility of the arms, intramolecular and intermolecular CC bonds are formed on irradiation. Thus, the generation of nanoparticles, which represent small oligomers, is much more likely than for the cross-linking of rigid, cross-conjugated stilbenoid dendrimers. The photoreactions in solution were studied by UV and NMR spectroscopy, the transformation of the films was studied by AFM. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 200…

Tristriazolotriazines: Luminescent Discotic Liquid Crystals

2018

Mechanistic Study of Stepwise Methylisocyanide Coupling and C-H Activation Mediated by a Low-Valent Main Group Molecule

2013

An experimental and DFT investigation of the mechanism of the coupling of methylisocyanide and C-H activation mediated by the germylene (germanediyl) Ge(Ar(Me6))2 (Ar(Me6) = C6H3-2,6(C6H2-2,4,6-Me3)2) showed that it proceeded by initial MeNC adduct formation followed by an isomerization involving the migratory insertion of the MeNC carbon into the Ge-C ligand bond. Addition of excess MeNC led to sequential insertions of two further MeNC molecules into the Ge-C bond. The insertion of the third MeNC leads to methylisocyanide methyl group C-H activation to afford an azagermacyclopentadienyl species. The X-ray crystal structures of the 1:1 (Ar(Me6))2GeCNMe adduct, the first and final insertion …

Determination of the composition of isomeric mixtures of allylstannanes by means of 119Sn and 13C NMR measurements

1993

Abstract Allylstannanes of the type Bun3Sn(C3H3) ((C3H3 = allenyl and propargyl) Me3Sn(C4H7), Bun3Sn(C4H7), Ph3Sn(C4H7), Me3Sn(C4H7)2 and Bun3Sn(C4H7)2 [C4H7 = (E)-but-2-enyl, (Z-but-2-enyl, and but-1-en-3-yl] were prepared via Grignard reactions as isomeric mixtures whose compositions can be directly determined by 119Sn and 13C NMR spectrometry. The 119Sn and 13C δ-values of all possible isomers together with the isomeric compositions of freshly prepared compounds and after isomerization in dry methanol under reflux are reported. The course of isomerization of some compounds in anhydrous methanol at room temperature or in the presence of Bu3SnCl was followed by 119Sn NMR spectrometry.

Isomerization and redox tuning in ‘Maya yellow’ hybrids from flavonoid dyes plus palygorskite and kaolinite clays

2014

Abstract The composition of the organic fraction of organic–inorganic hybrid materials prepared upon attachment of different natural, ‘historical’ flavonoid yellow dyes (zacatlaxcalli, fustic, marigold and cosmos) to palygorskite and kaolinite clays is described. Upon thermal treatment between 100 and 180 °C, significant isomerization and oxidation reactions occur thus resulting in the formation of polyfunctional materials potentially usable for therapeutic, catalytic and art purposes. The dye attachment to the clays would define a ‘Maya chemistry’ whose complexity could explain the versatile use of such materials in the pre-Columbian cultures.

Isomerization of α-pinene oxide over ZSM-5 based micro-mesoporous materials

2018

Abstract Few types of ZSM-5 based micro-mesoporous materials obtained via a dual template method, steam-assisted conversion and dual-functional templating were evaluated in α-pinene oxide isomerization. Complete conversion and the highest selectivity towards trans-carveol (ca. 40–43%) were achieved over X-ray amorphous micro-mesoporous aluminosilicates as well as mesoporous molecular sieves AlSi-SBA-15. In addition, X-ray amorphous samples containing the secondary building units of ZSM-5 zeolite demonstrated the highest rate of α-pinene oxide isomerization. The yield of the most desired product trans-carveol to a large extent depends on the accessibility of acid sites to the reagents molecu…

Rotation correlation time as a measure of microviscosity of excited state isomerization reactions of three cyanine dyes in n-alcohol solutions

1994

Abstract Rotation correlation times of three chemically similar cyanine dyes of different sizes in n -alcohol solutions have been recorded at several temperatures by using polarized picosecond spectroscopy. For all three dyes the linear temperature dependencies of τ or on η/ T were observed to be independent of solvent up to viscosities of about 60 cP. The rotational motion of the dyes proceeds at much slower rates than the excited state isomerization in viscous solutions of the same fluidity. Isomerization seems to depend on special solvent-induced changes of the force field of the reactant and clearly proceeds faster, especially for the two larger dyes, than predicted by Kramers' theory a…

ChemInform Abstract: 1,6-π-Electrocyclization of 3-Vinyl-Functionalized N,N′-Dimethyl-2,2′-bisindolyl: Some Analysis of the Educt Transformation Proc…

2010

The thermally and photochemically induced 1,6-π-electrocyclization reaction of 3-vinyl-functionalized N, N'-dimethyl-2,2′-bisindolyls 4 has been analysed and some reactivity aspects are presented. On the basis of time dependent 1H nmr and uv spectroscopic measurements the educt transformations can be observed in detail. Some results of the isomerization process of the educts are also given.

An experimental and theoretical study of the isomerization of mononuclear bis(arylselenolato)bis(triphenylphosphine)platinum complexes [Pt(SeR)2(PPh3…

2003

Abstract Mononuclear bis(thienylselenolato)bis(triphenylphosphine)platinum [Pt(SeTh)2(PPh3)2] (Th=2-thienyl, C4H3S) has been prepared by the treatment of cis-[PtCl2(PPh3)2] with NaSeTh. The 31P-NMR spectroscopic information indicates that cis-[Pt(SeTh)2(PPh3)2] is initially formed in the reaction. Upon prolonged standing in solution it isomerizes to trans-[Pt(SeTh)2(PPh3)2]. The reaction of cis-[PtCl2(PPh3)2] with LiSeFu (Fu=2-furyl, C4H3O) affords immediately a mixture of cis- and trans-isomers of [Pt(SeFu)2(PPh3)2] with the relative amount of the trans-isomer increasing with time. The recrystallization of the two reaction mixtures yielded cis,anti- and trans,syn-isomers of [Pt(SeTh)2(PPh3…

Arylazopyrazoles for Long-Term Thermal Energy Storage and Optically Triggered Heat Release below 0 °C.

2020

Arylazopyrazole derivatives based on four core structures (4pzMe, 3pzH, 4pzH, and 4pzH-F2) and functionalized with a dodecanoate group were demonstrated to store thermal energy in their metastable Z isomer liquid phase and release the energy by optically triggered crystallization at -30 °C for the first time. Three heat storage-release schemes were discovered involving different activation methods (optical, thermal, or combined) for generating liquid-state Z isomers capable of storing thermal energy. Visible light irradiation induced the selective crystallization of the liquid phase via Z-to-E isomerization, and the latent heat stored in the liquid Z isomers was preserved for longer than 2 …