Search results for "Dimer"
showing 10 items of 558 documents
ChemInform Abstract: Cyclic Esters of Aliphatic Diacids with Pyrocatechol and Hydroquinone.
1986
Cyclic esters of adipic acid, suberic acid and sebacic acid were prepared by reaction of the acid dichlorides and pyrocatechol or hydroquinone in benzene under high dilution conditions. While only the cyclic dimers could be obtained from hydroquinone, pyrocatechol formed cyclic monomers as well as cyclic dimers (and also a cyclic dimer with succinic acid). The structure of all compounds was confirmed by1H-NMR- and mass spectra. The crystal structures of the pyrocatechol esters were determined by single crystal X-ray analysis.
Electrochemical oxidation of 2,4,5-triaryl-substituted pyrroles.II. Oxidative dimerization of 4,5-diphenyl-2-mesitylylpyrrole
1989
2,4,5-Triaryl-substituted pyrroles lead, upon chemical or electrochemical oxidation, to an intermediate β-β'-dimer, which, in the course of the reaction, undergoes further oxidation to a tetracyclic derivative. To improve the selectivity towards the uncyclized dimer the oxidation of a triarylpyrrole in which the ortho positions of the phenyl group in position 2 are hindered by the presence of methyl groups was attempted. The cyclization was hindered, but an α-β'-dimer was obtained as the major product. An unexspected isomeric α-β'-dimer, in which the mesitylyl group is shifted into the β position of the pyrrole ring which undergoes the oxidation, was obtained in minor amounts. Electroanalyt…
Die thermische polymerisation von methylmethacrylat, 3. Verhalten des ungesättigten dimeren bei der polymerisation
1980
The thermal polymerization of methyl methacrylate is accompanied by the formation of appreciable amounts of an unsaturated dimer (H-1). The behaviour of H-1 during homopolymerization in presence of an initiator at 60, 80 and 100°C and during copolymerization with MMA in presence of an initiator at 60°C are investigated. The rate of (H-1)-homopolymerization is very low. The transfer constant to monomer H-1 is about CH-1 = 3·10−3 at 80°C as received from Pn-determinations. The termination is essentially by disproportionation. The copolymerization parameters as resulting from polymerizations with labeled MMA at 60°C are rMMA = 1,8 and rH-1 = 0,33, respectively.
Theoretical CASPT2 study of the excited state double proton transfer reaction in the 7-azaindole dimer
2006
Accurate CASPT2 calculations on the excited state double proton transfer reaction in the 7-azaindole dimer have been performed on different symmetric and asymmetric pathways along the protons interchange. The presence of a conical intersection connecting the initially photoinduced singlet excited state with a charge transfer state leading both to asymmetric ionic and neutral structures promotes a step-wise mechanism, probably taking place through the ionic intermediate. The concerted path is computed slightly higher in energy in the gas phase.
Energetics and Dynamics of Naphthalene Polyaminic Derivatives. Influence of Structural Design in the Balance Static vs Dynamic Excimer Formation
2003
Two new fluorescent macrocyclic structures bearing two naphthalene (Np) units at both ends of a cyclic polyaminic chain were investigated with potentiometric, fluorescence (steady-state and time-resolved) and laser flash photolysis techniques. The fluorescence emission studies show the presence of an excimer species whose formation depends on the protonation state of the polyamine chains implying the existence of a bending movement (occurring in both the ground and in the first singlet excited state), which allows the two naphthalene units to approach and interact. For comparison purposes, one bis-chromophoric compound containing a rigid chain (piperazine unit) was also investigated. Its em…
Wide Rim Urethanes Derived from Calix[4]arenes: Synthesis and Self-Assembly
2006
[reaction: see text] Calix[4]arenes 4, substituted at the wide rim by four N-tolyl-urethane groups, were synthesized, as well as derivatives 10a,b bearing two or three tolyl-urea groups beside of one or two urethane group(s). In contrast to tetra-tolyl urea 11, the urethane derivatives do not form hydrogen-bonded, dimeric capsules in CDCl3 or benzene-d6, but the dimerization can be induced for the triurea 10b by tetraethylammonium cations as guests. The quantitative formation of heterodimers is observed for all urethanes 4 and 10a,bin benzene-d6 in mixtures with a "tetra-loop" tetraurea 14, while "bisloop" tetraureas 13 require di- or triurea derivatives 10a,b for a clean heterodimerization.
Equilibrium and spectroscopic studies of diethyltin(iv) complexes formed with hydroxymono- and di-carboxylic acids and their thioanalogues
2002
The complex formation of diethyltin(IV) cation with glycolic (GA), lactic (LA), succinic (SA), malic (MA), tartaric (TA), mercaptoacetic (MAA), 2-mercaptopropionic (MPA), mercaptosuccinic (MSA) and dimercaptosuccinic acid (DMSA) has been investigated by potentiometric, spectrophotometric, 1H NMR and Mossbauer spectroscopic methods. The mercaptocarboxylic acids yielded much more stable complexes than the corresponding hydroxy acids. Below pH 3, the carboxylate and the still protonated hydroxyl group of hydroxy acids are co-ordinated to the metal ion, while in the case of their thio analogues, {COO−, S−} co-ordinated species are dominant. With increasing pH, the metal promoted deprotonation o…
Revision of Na 2 A1Σ+u state molecular constants by polarization labeling spectroscopy
1997
ABSTRACT. This paper contains the analysis of the A1 of Na2 based on the data obtained from thepolarization labeling spectroscopy experiment on the A' —X' transition. A set of Dunham coefficients is derived, which describes the A state in the wide range of v and J 126) quantum numbers and reproduces the positions of unperturbed rotational lines in the A-X band system towithinO.1 cm'.1. INTRODUCTION.We report' new analysis of the A' state based on the data obtained from polarization labelingspectroscopy (PLS) experiment"2, based on V-type optical—optical double resonance scheme, on the 1 : ' ; band system of sodium dimer. The diatomic alkali molecules, with their simple electronic configurat…
Die kristallstruktur von oligo[(2-hydroxy-1,3-phenylen)methylen]en
1984
The crystal structure of three tetranuclear phenolic compounds – 6,6′-bis (2-hydroxy-5-methylbenzyl)-4,4′-dimethyl-2,2′-methylenediphenol (1), 6-(2-hydroxy-3,5-dimethylbenzyl)-6′-(2-hydroxy-5-methylbenzyl)-4,4′-dimethyl-2,2′-methylendiphenol (2), and 6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-6′-(2-hydroxy-5-methylbenzyl)-4,4′-dimethyl-2,2′-methylene-diphenol (3) –, was determined by single crystal X-ray analysis. Intramolecular hydrogen bonds between all hydroxyl groups of adjacent phenolic units are found for all molecules. They are directed to the opposite end of the molecule by the ortho-methyl or ortho-tert-butyl group in compounds 2 and 3, while no special orientation is found in 1. Th…
Excited states of [3.3](4,4')biphenylophane: the role of charge-transfer excitations in dimers with pi-pi interaction.
2010
The singlet and triplet electronic excitation manifold of [3.3](4,4')biphenylophane (BPP), an intramolecular dimer, and 4,4'-dimethylbiphenyl (DMBP), the corresponding monomer, has been analyzed by employing the approximate coupled-cluster singles and doubles model (CC2). The calculated triplet-triplet and singlet-singlet transient absorption spectra show good agreement with recent experimental results. The calculations suggest a strong interaction of the two biphenyl moieties of BPP in the first singlet and triplet excited states due to the overlapping pi-electron systems, and Forster-Dexter theory for weak coupling cannot be applied. Both the first excited singlet and triplet states of BP…