Search results for "Structural isomer"
showing 10 items of 57 documents
Chromatographic and spectroscopic properties of regioisomers of some 1H-1,5-benzodiazepines
1994
The separation of the two regioisomeric derivatives of 1H-1,5-benzodia- zepine yielded from the reaction of 1,2-diamino-4-methylbenzene with 4-substituted acetophenones was performed by reversed phase high per- formance liquid chromatography, and the absorption spectra of the sepa- rated isomers have been determined for three isomer pairs which have been obtained starting from acetophenones with substituents of different electronegativity. The isomer ratio then could be estimated as well from the ratio of the peak areas as from the absorption spectra. They agree well with the known ratio determined from nmr intensities
A topological isomer of the Au25(SR)18−nanocluster
2020
Energetically low-lying structural isomers of the much-studied thiolate-protected gold cluster Au25(SR)18− are discovered from extensive (80 ns) molecular dynamics (MD) simulations using the reactive molecular force field ReaxFF and confirmed by density functional theory (DFT). A particularly interesting isomer is found, which is topologically connected to the known crystal structure by a low-barrier collective rotation of the icosahedral Au13 core. The isomerization takes place without breaking of any Au–S bonds. The predicted isomer is essentially iso-energetic with the known Au25(SR)18− structure, but has a distinctly different optical spectrum. It has a significantly larger collision cr…
Complexes of organometallic compounds. XLVI. Synthesis of adducts formed by organotin(IV) trichlorides with 1,2-bis(diphenylphosphino)ethane, and the…
1977
Abstract Adducts between RSnCl 3 (R = Me, Bu n , Oct n , Ph) and 1,2-bisz(diphenylphosphino)ethane, DPE, have 1:1 composition. In Mossbauer spectroscopic experiences at variable absorber temperature the area under the resonant peaks, A, has been measured for RSnCl 3 ·DPE, R = Me, Ph; slopes plots of in A vs. T suggest strong coupling between Mossbauer atoms, which has been interpreted in terms of solid state polymeric structures, due to DPE acting as a bridging bis-monodentate ligand. Infrared data indicate the covalency of SnCl bonds. Three possible structural isomers of octahedral type are then proposed, one having trans -P 2 and two cis -P 2 atoms. A choice between these structures has …
Isomerism and Ligand Rearrangement within the cyclo-P2S3 Middle Deck in Dimolybdenum Triple-Decker Complexes
2009
The molecular structure of [Cp*2Mo2P2S3] (1; Cp* = η5-C5Me5) has been reinvestigated. In DFT studies a series of various positional isomers A−E have been calculated for the model complex [(C5H5)2Mo2P2S3]. The energetically favored isomer [Cp*2Mo2(μ,η2:2-PS)2(μ-S)] (1B) reacts with W(CO)5THF to give [Cp*2Mo2P2S3·W(CO)5] (2). X-ray diffraction analysis of 2 confirms the presence of two η2:2-PS dumbbells and one singly bridging sulfur ligand, the W(CO)5 fragment being coordinated at one of the P atoms. Arrangement B is also found in the structure of the diadduct [Cp°2Mo2P2S3{W(CO)5}2] (3; Cp° = t-BuMe2C5H2), which is more stable than its Cp* analogue. 31P solid-state MAS NMR spectroscopic stud…
First Titanium-Catalyzed anti-1,4-Hydrosilylation of Dienes
2005
1,4-Hydrosilylation of dienes catalyzed by late transition metals constitutes a straightforward access to allylsilanes. However, when unsymmetric dienes are used, it generally leads to a mixture of regioisomers (tail or head products) via Z-specific 1,4-addition. Here we describe the first catalytic anti-1,4-hydrosilylation of dienes using the cheap and stable Cp2TiF2 complex as catalyst. It affords E-allylsilanes in good to excellent yields with an unprecedented regio- and diastereoselectivity. Dehydrogenative double silylation of dienes can be selectively obtained by simply changing the activation protocol of the precatalyst.
Regio- and Stereoselective Synthesis of Spiropyrrolizidines and Piperazines through Azomethine Ylide Cycloaddition Reaction.
2015
A series of original spiropyrrolizidine derivatives has been prepared by a one-pot three-component [3 + 2] cycloaddition reaction of (E)-3-arylidene-1-phenyl-pyrrolidine-2,5-diones, l-proline, and the cyclic ketones 1H-indole-2,3-dione (isatin), indenoquinoxaline-11-one and acenaphthenequinone. We disclose an unprecedented isomerization of some spiroadducts leading to a new family of spirooxindolepyrrolizidines. Furthermore, these cycloadducts underwent retro-1,3-dipolar cycloaddition yielding unexpected regioisomers. Upon treatment of the dipolarophiles with in situ generated azomethine ylides from l-proline or acenaphthenequinone, formation of spiroadducts and unusual polycyclic fused pip…
DOTAGA-anhydride: a valuable building block for the preparation of DOTA-like chelating agents.
2012
International audience; A DOTA derivative that contains an anhydride group was readily synthesized by reacting DOTAGA with acetic anhydride and its reactivity was investigated. Opening the anhydride with propylamine led to the selective formation of one of two possible regioisomers. The structure of the obtained isomer was unambiguously determined by 1D and 2D NMR experiments, including COSY, HMBC, and NOESY techniques. This bifunctional chelating agent offers a convenient and attractive approach for labeling biomolecules and, more generally, for the synthesis of a large range of DOTA derivatives. The scope of the reaction was extended to prepare DOTA-like compounds that contained various f…
Regioisomeric 5(3)-aminomethyl-3(5)-phenylisoxazoles: synthesis, spectroscopic discrimination, and muscarinic activity.
1995
The regioselective synthesis of isomeric 5(3)-aminomethyl-3(5)-phenyl isoxazoles using different methods is described. Spectroscopic data, especially mass spectrometric fragmentation, were used to identify and characterize the regioisomers. The muscarinic activity of these isoxazoles was assayed on isolated guinea-pig ileum and atria as well as on isolated rabbit vas deferens. Regioisomere 5(3)-Aminomethyl-3(5)-phenyl-isoxazole: Synthese, spektroskopische Unterscheidung und muskarinische Aktivitat Es werden verschiedene Verfahren zur regioselektiven Darstellung von 5(3)-Aminomethyl-3(5)-phenyl-isoxazolen beschrieben, die anhand ihrer spektroskopischen Daten, insbesondere der massenspektrosk…
Conformationally rigid molecular and polymeric naphthalene-diimides containing C6H6N2 constitutional isomers
2021
Organic thin films based on naphthalenediimides (NDIs) bearing alkyl substituents have shown interesting properties for application in OLEDs, thermoelectrics, solar cells, sensors and organic electronics. However, the polymorphic versatility attributed to the flexibility of alkyl chains remains a challenging issue, with detrimental implications on the performances. Aryl analogues containing C6H6N2 constitutional isomers are herein investigated as one of the possible way-out strategies. The synthesis of molecular and polymeric species is described, starting from naphthaleneteracarboxyldianhydride with isomeric aromatic amines and hydrazine. The materials are fully characterized by spectrosco…
A theoretical analysis of the structure and properties of B26H30 isomers. Consequences to the laser and semiconductor doping capabilities of large bo…
2019
Decaborane(14), nido-B10H14, is the major commercially available molecular building block in boron cluster chemistry. The condensation of two such {nido-B10} blocks gives the known isomers of B18H22 – a molecule used in the fabrication of p-type semiconductors and capable of blue laser emission. Here, we computationally determine the structures and thermodynamic stabilities of 20 possible B26H30 regioisomers constructed from the fusion of three {nido-B10} blocks with the three subclusters conjoined by two-boron atom shared edges. In addition, density functional theory, time-dependent (TD)-DFT and multiconfigurational CASPT2 methods have been used to model and investigate the physical and ph…