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Solvent Dependent (solvent + dependent)
Selected AbstractsN -Isopropyl enols of carboxylic acid amides,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2003Yi Xiong Lei Abstract Eight N -isopropyl compounds of the formal structure YY,CHCONHPr- i (6), Y,Y,,=,CO2Me, CO2CH2CF3, CN; YY,,=,Meldrum,s acid residue; Y,=,CO2Me, Y,,=,CO2CH2CF3, CN; Y,=,CO2CH2CF3, CO2CH(CF3)2, Y,,=,CN, and the N - t -butyl derivative of Meldrum's acid were prepared and their structures were investigated in the solid state and in solution. The x-ray diffraction data indicate that in the solid state the structure is that of the amide 6, when Y,=,Y,,=,CO2Me, whereas when Y,=,CO2Me, Y,,=,CN or YY,,=,Meldrum,s acid residue the structure is that of the enol (5) YY,C=C(OH)NHPr- i. The solid-state 13C spectra indicate structure 6 when Y,=,CO2Me, Y,,=,CO2R, R,=,Me, CH2CF3 and an enol structure for the other compounds studied. 1H, 13C and when available 19F NMR spectra showed that the enol/amide composition in solution is structure and solvent dependent, in analogy with the previously investigated N -Ph analogs. The percentage of enol (and KEnol) decrease in the order of solvents CCl4,>,CDCl3,>,THF- d8,>,CD3CN,>,DMSO- d6, DMF- d7. For Y,Y, the percentage of enol increases when the number of fluorine atoms in R of the CO2R increases, when CN replaces a CO2R group or for the cyclic Meldrum's acid derivative. Both E - and Z -enols were observed when Y,,,Y,, mostly at low temperature. The ,(OH) values increase with increased polarity of the medium and with increased strength of the hydrogen bonds in which they are involved. In THF- d8 and DMF- d7 the Z -enol/E -enol and the amide/enol ratios increase with increase in temperature. A main conclusion from the work is that the percentage of the enol increases, but not drastically, when the N -substituent is changed from Ph to i -Pr. Copyright © 2003 John Wiley & Sons, Ltd. [source] Synthesis and Characterization of Silver Nanoparticles and Titanium Oxide Nanofibers: Toward Multifibrous NanocompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2010Fredrick O. Ochanda A new method was investigated to produce new multiscale fibrous nanocomposites comprised of titanium oxide (TiO2) nanofibers and silver (Ag) nanoparticles (NPs). The process involved electrospinning TiO2 precursor solution containing colloidal solution of Ag NPs, and organic solvent (dimethyl- n,n -formamide) to fabricate a porous, nonwoven, free-standing nanofiber mesh. Postprocess heating of the electrospun nanofibers entailed calcination in air environment at 500°C for 3 h. Microemulsion processing was used to generate NPs of Ag in a monodispersed distribution throughout the colloidal solution. X-ray diffraction data were consistent with the anatase phase of TiO2, while transmission electron microscopy and hydrogen desorption measurements revealed a very porous microstructure. It was demonstrated that NP colloidal stability is solvent dependent. It is anticipated that incorporation of metal particles in nanofibers will lead to enhanced photocurrent generation, when used in functional devices. [source] Chiral Encapsulation by Directional InteractionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 45 2009Agnieszka Szumna Abstract The complexation of chiral guests in the cavity of dimeric self-assembled chiral capsule 12 was studied by using NMR spectroscopy and X-ray crystallography. Capsule 12 has walls composed of amino acid backbones forming numerous directional binding sites that are arranged in a chiral manner. The polar character of the interior dictates the encapsulation preferences towards hydrophilic guests and the ability of the capsule to extract guests from water into an organic phase. Chiral discrimination towards hydroxy acids was evaluated by using association constants and competition experiments, and moderate de values were observed (up to 59,%). Complexes with one or two guest molecules in the cavity were formed. For 1:1 complexes, solvent molecules are coencapsulated; this influences guest dynamics and makes the chiral recognition solvent dependent. Reversal of the preferences can be induced by coencapsulation of a nonchiral solvent in the chiral internal environment. For complexes with two guests, filling of the capsule's internal space can be very effective and packing coefficients of up to 70,% can be reached. The X-ray crystal structure of complex 12,((S) -6)2 with well-resolved guest molecules reveals a recognition motif that is based on an extensive system of hydrogen bonds. The optimal arrangement of interactions with the alternating positively and negatively charged groups of the capsule's walls is fulfilled by the guest carboxylic groups acting simultaneously as hydrogen-bond donors and acceptors. An additional guest molecule interacting externally with the capsule reveals a possible entrance mechanism involving a polar gate. In solution, the structural features and dynamic behavior of the D4 -symmetric homochiral capsule were analyzed by variable-temperature NMR spectroscopy and the results were compared with those for the S8 -symmetric heterochiral capsule. [source] Paradoxical Solvent Effects on the Absorption and Emission Spectra of Amino-Substituted Perylene Monoimides,CHEMPHYSCHEM, Issue 8 2005Peter D. Zoon Abstract In N -(2,5-di- tert -butylphenyl)-9-pyrrolidinoperylene-3,4-dicarboximide (5PI) the absorption and emission spectra display large solvatochromic shifts, but, remarkably, the Stokes shift is practically independent of solvent polarity. This unique behavior is caused by the extraordinarily large ground-state dipole moment of 5PI, which further increases upon increasing the solvent polarity, whereas the excited-state dipole moment is less solvent dependent. In the corresponding piperidine compound, 6PI, this effect is much less important owing to the weaker coupling between the amino group and the aromatic imide moiety, and in the corresponding naphthalimide, 5NI, it is absent. The latter shows the conventional solvatochromic behavior of a push,pull substituted conjugated system, that is, minor shifts in absorption and a larger change in the emission energy with solvent polarity. [source] | ||||||||||