Search results for "Molecule"
showing 10 items of 5162 documents
STUDIEN ZUM VORGANG DER WASSERSTOFFÜBERTRAGUNG 611
1982
Abstract In arylsulfonyl halides, the half-wave potentials of the corresponding chlorides and fluorides differ by more than 1000 mV, the fluoride being more negative; the influence of para-substituents is small for the chlorides, large for the fluorides. In agreement with the half-wave potentials, arylsulfonyl chlorides are considerably more reactive chemically than the corresponding fluorides. The O-selectivity found for P(O)F compounds is not observed in arylsulfonyl fluorides. Studies of competitive ester formation using primary and secondary alcohols and various arylsulfonyl chlorides yielded no clear analogy to the half-wave potentials. The primary alcohol is always sulfonated in prefe…
Mechanism of the oxidation of sulfides by dioxiranes: conformational mobility and transannular interaction in the oxidation of thianthrene 5-oxide.
2004
The detailed study of the oxidation of thianthrene 5-oxide (1) with methyl(trifluoromethyl)dioxirane (5b) in different solvents and in the presence of (18)O isotopic tracers is reported. Thianthrene 5-oxide (1) is a flexible molecule in solution, and this property allows for transannular interaction of the sulfoxide group with the expected zwitterionic 7 and hypervalent 10-S-4 sulfurane 9 intermediates formed in the oxidation and biases the course of the reaction toward the monooxygenation pathway.
ISomerization of xylene: MINDO/3 study of the cyclization of benzenium cation into bicyclo[3.1.0]hexenyl cation
1989
Abstract A MINDO/3 study of thermal electrocyclic closing of the benzenium cation to form a bicyclo[3.1.0]hexenyl cation is presented. The calculated mechanism discusses the possibility of cyclization of xylenium cations on a silica catalyst or in superacid media. The structure and energy of the transition state, the enthalpies of isomerization and barriers of activation were calculated for the following processes: isomerization of 2,6-dimethylbenzenium cation into 2,6-dimethylbicyclo[3.1.0]hexenyl cation, isomerization of 2,4-dimethylbenzenium cation into 2,4-dimethylbicyclo[3.1.0]-hexenyl cation, and isomerization of benzenium cation into bicyclo[3.1.0]-hexenyl cation. Equilibrium and kin…
An Approach to 2,4-Substituted Pyrazolo[1,5-a]pyridines and Pyrazolo[1,5-a]azepines by Ring-Closing Metathesis
2013
The ring-closing metathesis (RCM) reactions of dienylpyrazoles have been employed in the synthesis of pyrazolo[1,5-a]pyridine and pyrazolo[1,5-a]azepine derivatives. Based on this approach, the diastereoselective synthesis of potential peptidomimetics containing four amino acid residues with the second (i+1) and third (i+2) fragments having been substituted by bicyclic frameworks is described.
Scintillation Measurements at Very High Solute Concentrations; Self Quenching-Structure Correlatios
1968
Abstract Measurements of the relative scintillation yields of some liquid organic systems were carried out with several highly soluble scintillator solutes. Self quenching was observed at high concentrations with some of the solutes, but not with others. The results were correlated with the ability of the solute molecules to come together, in a special configuration, close enough to form an association. A study of the atomic models of the solute molecules showed that those moleculeswith chromophor systems which were non-coplanar, or co-planar but shielded by substituent groups, did not produce self quenching. However, those solute molecules with unprotected co-planar chromophor systems did …
Polyoxometalate-Based Molecular Materials.
1998
Molecule-based materials with active physical properties, in particular electrical, magnetic, and optical, are a focus of contemporary materials chemistry research. Certainly, one reason for this interest has been the realization that these materials can exhibit cooperative properties typically associated with the inorganic network solids, as for example metallic conduction or even superconductivity,1 ferromagnetism,2 and nonlinear optical properties.3 With respect to the electrical properties, many important achievements were obtained in the 1970s with the discovery of the first molecule-based metal in 1972,4 namely the π-electron donor-acceptor complex [TTF][TCNQ] (TTF ) tetrathiafulvalen…
Novel bis(tetrahydropyrrolo[3,4-b]carbazoles) linked with aliphatic chains: synthesis and structural aspects
2001
Syntheses of novel bis(tetrahydropyrrolo[3,4-b]carbazoles) by a [4+2]cycloaddition reaction are described. By variation of dienophiles bis(tetrahydropyrrolo[3,4-b]carbazoles) of varying aliphatic spacer length could be obtained in high yields. These conformationally highly flexible molecules represent an interesting class of compounds, believed to have an affinity towards DNA, as potential DNA ligands.
Synthesis of porphyrin-bis(polyazamacrocycle) triads via Suzuki coupling reaction
2014
Suzuki–Miyaura cross-coupling reaction has been used for the synthesis of tricyclic architectures based on trans-A2B2-porphyrins and bisaminal-protected polyazamacrocycles which are linked directly or by a p-phenylene spacer. This modular approach allowed the synthesis of ligands with various substituted porphyrin macrocycles and bisaminal-protected tetraazamacrocycles possessing different cavity sizes. These molecules can be assembled into dimers using a DABCO linker. Deprotection of these compounds afforded porphyrin-bis(polyazamacrocycle) triads.
2-hydroxyethylierung von oligo(iminoethylen)en und deren überführung in oligo-[N-(2-chloroethyl)iminoethylen]e
1981
Oligo[N-(2-chloroethyl)iminoethylene]s (8) were synthesized as potential antitumor agents like their low molecular weight analogues. It was found that oligo(iminoethylene)s (5) can be 2-hydroxyethylated with ethylene oxide and subsequently transformed into oligo[N-(2-chloroethyl)iminoethylene hydrochloride]s (14) with thionyl chloride. The stability of the free oligomers 8 was found to decrease with the number of N-2-chloroethyl groups in the molecule.
On the Reactivity of C(sp3)–H σ-Bonds: Oxygenation with Methyl(trifluoromethyl)dioxirane
2008
The reactivity of C–H σ-bonds of a series of 2-substituted adamantanes 2 towards methyl(trifluoromethyl)dioxirane (1) shows a consistent dependence on the electron-withdrawing ability, either inductive or by resonance, of the substituent. The results are interpreted in terms of the ability of the substrate molecule to delocalize the electronic perturbation of the reacting center at the beginning of the reaction path. The model shows that the electronic demand from the reacting C–H σ-bond is transmitted along the substrate through a chain of hyperconjugative interactions, the relative intensities of which depend on the σ-bonds involved. The substrate molecule simultaneously provides positive…