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Apolar Solvents (apolar + solvent)
Selected AbstractsChemInform Abstract: Assisted Ruthenium-Catalyzed C,H Bond Activation: Carboxylic Acids as Cocatalysts for Generally Applicable Direct Arylations in Apolar Solvents.CHEMINFORM, Issue 42 2008Lutz Ackermann Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Switchable Fluorescent and Solvatochromic Molecular Probes Based on 4-Amino- N -methylphthalimide and a Photochromic DiaryletheneEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2008Sergey F. Yan Abstract New fluorescent photochromic compounds (1 -H and 1 -Boc) have been synthesized and characterized in different solvents. The fluorescence emission can be switched "on" and "off" with visible light and UV, respectively, by means of the photochromic reaction. The emission wavelength and efficiency strongly depend on the polarity of the solvent. The compounds show a positive solvatochromic effect in the emission maxima, and their fluorescence quantum yield decreases as the solvent's polarity increases (from cyclohexane to dioxane). In solvents more polar than dioxane the emission is too weak and therefore undetectable, and thus 1 -H and 1 -Boc behave as "normal" photochromic compounds. The photochromic reaction is also sensitive to the environment. A decrease of more than an order of magnitude was found for the quantum yield of the colouring reaction (,OF,CF) for 1 -H in ethanol compared with cyclohexane, and an about threefold decrease in ,OF,CF was observed for the compound 1 -Boc in polar solvents (compared with apolar solvents). For both compounds the ring-opening reaction was found not to dependent on the solvent. The novel fluorescent molecular switches 1 -H and 1 -Boc are able to probe the polarity of their microenvironment. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] SN2 Displacement by Bromide Ions in Dichloromethane , The Role of Reverse MicellesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2006Lucia Brinchi Abstract Reverse micellar systems are of interest as reaction media because they are powerful models for biological compartmentalization, enzymatic catalysis and separation of biomolecules. Solutions of ionic surfactants in apolar solvents may contain reverse micelles, but they may also contain ion pairs, or small clusters, with waters of hydration. We studied the bimolecular reaction in CH2Cl2 solutions of cationic tetraalkylammonium bromide salts (onium salts), such as cetyltrimethylammonium bromide (CTABr), cetyltripropylammonium bromide (CTPABr) and tetra- n -butylammonium bromide (TBABr). Methylnaphthalene-2-sulfonate (,-MeONs), its 6-sulfonate derivative (,-MeONsS,) as the 2,6-lutidinium salt and methyl-5- N,N,N,trimethylammonium naphthalene-1-sulfonate (,-MeONsNT+) as the trifluoromethanesulfonate salt react with Br, in CH2Cl2. First-order rate constants, kobs, increase linearly and similarly for the three substrates with increasing concentrations of the onium salts. Reactions are faster with TBABr than they are with CTPABr and CTABr, and the reactivity of the three substrates is in the order: ,-MeONsNT+ >> ,-MeONsS, > ,-MeONs. The reactions are inhibited by the addition of H2O, but CTABr tolerates H2O in large excess. At [H2O]/[CTABr] = w0 , 6, "water-pool" reverse micelles form, and kobs for all three substrates is then independent of w0. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Positively Charged Iridium(III) Triazole Derivatives as Blue Emitters for Light-Emitting Electrochemical CellsADVANCED FUNCTIONAL MATERIALS, Issue 11 2010Mathias Mydlak Abstract Cationic blue-emitting complexes with (2,4-difluoro)phenylpyridine and different 1,2,3-triazole ligands are synthesized with different counterions. The influence of the substituents on the triazole ligand is investigated as well as the influence of the counterions. The substituents do not change the emission energy but, in some cases, slightly modify the excited-state lifetimes and the emission quantum yields. The excited-state lifetimes, in apolar solvents, are slightly dependent on the nature of the counterion. A crystal structure of one of the compounds confirms the geometry and symmetry postulated on the basis of the other spectroscopic data. Light-emitting electrochemical cell devices are prepared and the recorded emission is the bluest with the fastest response time ever reported for iridium complexes. [source] Hydrogen Bonding of Fluorinated Saccharides in Solution: F Acting as H-Bond Acceptor in a Bifurcated H-Bond of 4-Fluorinated Levoglucosans,HELVETICA CHIMICA ACTA, Issue 10 2007Bruno Bernet Abstract 4-Fluorinated levoglucosans were synthesised to test if OH,,,F H-bonds are feasible even when the O,,,F distance is increased. The fluorinated 1,6-anhydro- , - D -glucopyranoses were synthesised from 1,6,:,3,4-dianhydro- , - D -galactopyranose (8). Treatment of 8 with KHF2 and KF gave 43% of 4-deoxy-4-fluorolevoglucosan (9), which was transformed into the 3- O -protected derivatives 13 by silylation and 15 by silylation, acetylation, and desilylation. 4-Deoxy-4-methyllevoglucosan (19) and 4-deoxylevoglucosan (21) were prepared as reference compounds that can only form a bivalent H-bond from HOC(2) to OC(5). They were synthesised from the iPr3Si-protected derivative of 8. Intramolecular bifurcated H-bonds from HOC(2) to FC(4) and OC(5) of the 4-fluorinated levoglucosans in CDCl3 solution are evidenced by the 1H-NMR scalar couplings h1J(F,OH) and 3J(H,OH). The OH,,,F H-bond over an O,,,F distance of ca. 3.0,Å is thus formed in apolar solvents, at least when favoured by the simultaneous formation of an OH,,,O H-bond. [source] Novel Fabrication of Size-Tunable Silica Nanotubes Using a Reverse- Microemulsion-Mediated Sol,Gel Method ,ADVANCED MATERIALS, Issue 9-10 2004J. Jang Size-tunable silica nanotubes have been fabricated using a novel reverse-microemulsion-mediated sol,gel method (see Figure). This facile approach is adaptable to large-scale fabrication, and the diameter of silica nanotubes is tunable through the use of different apolar solvents. The photoluminescence spectrum of the nanotubes displays three emission bands, including a stable and strong blue light emission at 435 nm. [source] Fine-Tuning the Dimerization of Tetraureacalix[4]arenesCHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2010Yuliya Rudzevich Dr. Abstract Calix[4]arenes substituted by four urea residues at their wide rim form hydrogen-bonded homo- and heterodimeric capsules in apolar solvents. If urea groups are covalently connected to loops or substituted by bulky residues, the dimerization may be restricted to those pairs in which the loops do not overlap and for which the residues are small enough to pass the loops. In the present study, we describe the dimerization properties of tetraureas with one, two (adjacent or opposite), three, or four loops and those bearing (additionally) up to four residues of different size: a=tolyl, b=3,5-di- tert -butylphenyl, c=4-propyloxy-3,5-di-(tert -butylphenyl)phenyl, and d=4-[tris-(4- tert -butylphenyl)methyl]phenyl. For compounds with four loops of different size (O(CH2)nO-chains with n=10, 14, and 20 connecting the m -positions of the urea phenyl residues) a clear "stepwise" sorting scheme could be established, in which the bulkiest residue d is excluded by all tetraloop compounds and the smallest residue a can pass only the smallest loops (n=10). The medium-sized residues b or c are tolerated by n=14 and 20 or only by n=20. Selectivities can be built up also on geometrical factors. A trisloop compound, for instance, combines only with a tetraurea bearing a single bulky residue and tetraureas with two bulky substituents in adjacent or opposite position are distinguished by the bisloop derivatives with adjacent or opposite loops. The impossibility to form a homodimer of a monoloop compound containing two bulky residues leads to its selective heterodimerization with a derivative bearing three bulky groups. Subtle effects for "borderline" cases, in which the dimerization or reorganization takes a longer time, are also discussed. [source] Molecules with New Topologies Derived from Hydrogen-Bonded Dimers of Tetraurea Calix[4]arenesCHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2008Anca Bogdan Dr. Abstract Tetraurea calix[4]arenes 2 have been synthesized in which two adjacent aryl urea residues are connected to a loop by an aliphatic chain -O-(CH2)n -O-. The remaining urea residues have a bulky 3,5-di- tert -butylphenyl residue and an , -alkenyloxyphenyl residue. Since this bulky residue cannot pass through the loop, only one homodimer (2,2) is formed in apolar solvents, for steric reasons, in which the two alkenyl residues penetrate the two macrocyclic loops. Covalent connection of these alkenyl groups by olefin metathesis followed by hydrogenation creates compounds 3, which consist of molecules with hitherto unknown topology. Their molecular structure was confirmed by 1H,NMR spectroscopy and ESIMS, and for one example by single-crystal X-ray analysis. [source] Highly Fluorescent Lyotropic Mesophases and Organogels Based on J-Aggregates of Core-Twisted Perylene Bisimide DyesCHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2008Xue-Qing Li A new perylene bisimide dye has been synthesized that forms highly fluorescent J-aggregates in various organic solvents and its gelation in polar solvents like acetone and dioxane is observed (see figure), whilst anisotropic highly viscous lyotropic mesophases are created in apolar solvents such as n -hexane or methylcyclohexane. [source] Towards a Tunable Tautomeric Switch in Azobenzene Biomimetics: Implications for the Binding Affinity of 2-(4,-Hydroxyphenylazo)benzoic Acid to StreptavidinCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2008Joan-Antoni Farrera Dr. Abstract The tautomeric equilibria of 2-(4,-hydroxyphenylazo)benzoic acid (HABA) and 2-(3,,5,-dimethyl-4,-hydroxyphenylazo)benzoic acid (3,,5,-dimethyl-HABA) have been studied by a combination of spectroscopic and computational methods. For neutral HABA in solvents of different polarity (toluene, chloroform, DMSO, DMF, butanol, and ethanol) the azo tautomer (AT) is largely predominant. For monoanionic HABA, the hydrazone tautomer (HT) is the only detected species in apolar solvents such as toluene and chloroform, while the AT is the only detected species in water and a mixture of both tautomers is detected in ethanol. Comparison of the results obtained for HABA and its 3,,5,-dimethylated derivative shows that dimethylation of the hydroxybenzene ring shifts the tautomeric preferences towards the hydrazone species. These findings have been used to examine the differences in binding affinity to streptavidin, as the lower affinity of HABA can be explained in terms of the larger energetic cost associated with the tautomeric shift to the bioactive hydrazone species. Overall, these results suggest that a balanced choice of chemical substituents, embedding environment, and pH can be valuable for exploitation of the azo,hydrazone tautomerism of HABA biomimetics in biotechnological applications. [source] | |||||||||||||||||||||||||