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91.
Sanz D Claramunt RM Singh SP Kumar V Aggarwal R Elguero J Alkorta I 《Magnetic resonance in chemistry : MRC》2005,43(12):1040-1043
The combined use of 1H NMR spectroscopy with theoretical calculations of chemical shifts (GIAO) and coupling constants (B3LYP/6-311 ++G**) of a 5-hydroxy-5-trifluoromethyl-Delta2-isoxazoline has enabled solving the problem of the assignments of the diastereotopic protons in this compound. This result has been extended to 5-hydroxy-5-trifluoromethyl-Delta2-pyrazolines and the corresponding 5-trichloromethyl derivatives. 相似文献
92.
Zhang F Bai S Yap GP Tarwade V Fox JM 《Journal of the American Chemical Society》2005,127(30):10590-10599
Described are the design, synthesis, and study of nonbiological molecules based on salophen and salen ligands that fold into single-stranded helices in the presence of either Ni(II) or Cu(II). X-ray diffraction studies show that the materials fold into helical structures in the solid state, and a series of NMR studies provide strong evidence that the folded structures are conserved in solution. Metal coordination is required for folding, as NMR and X-ray show that the free ligands do not adopt helical structures. Two of the racemic metallofoldamers spontaneously resolve during crystallization from CHCl3/acetonitrile, and CD spectroscopy and optical rotation show that the resolved, crystalline materials racemize quickly when dissolved at 5 degrees C. This shows that the secondary structures can reorganize easily and can, therefore, provide the basis for responsive materials. By comparison, an analogue from enantiomerically pure (R,R)-(-)-trans-cyclohexanediamine showed a strong CD signal and a large specific rotation. Electrochemical experiments show that a structural reorganization occurs upon metal-centered reduction of a Cu(II)-containing foldamer. When the reduction is carried out in the presence of coordinating ligands, it is proposed that apical binding of those ligands gives square pyramidal complexes. Semiempirical (AM1) calculations support that the helical structure would be disrupted by the reduction to Cu(I) with concomitant reorganization to a square pyramidal complex. 相似文献
93.
Vinod K. Ahluwalia Daljeet Singh Rishi P. Singh 《Monatshefte für Chemie / Chemical Monthly》1984,115(8-9):1059-1064
Condensation of hydroxybenzaldehydes viz., 2,3,4-trihydroxy-, 2,4-dihydroxy-, 2,4-dihydroxy-6-methyl-, and 2,4-dihydroxy-3-iodo-6-methylbenzaldehydes with buta-1,3-diene in the presence of orthophosphoric acid yields crotylbenzaldehydes in one step. The latter compounds on cyclisation afford the corresponding 2-methylformylchromans.
Eine einfache Synthese von Crotylbenzaldehyden und 2-Methylformyl-chromanen
Zusammenfassung Die Kondensation von Hydroxybenzaldehyden (2,3,4-Trihydroxy-, 2,4-Dihydroxy-, 2,4-Dihydroxy-6-methyl-, und 2,4-Dihydroxy-3-jod-6-methyl-benzaldehyd) mit Buta-1,3-dien in Gegenwart von Orthophosphorsäure ergibt in einer Stufe Crotylbenzaldehyde. Diese lassen sich durch Cyclisierung zu den entsprechenden 2-Methylformylchromanen umsetzen.相似文献
94.
Homochiral bis(oxazolinyl)pyridine type ligands were synthesized from (S)-valine and converted into their Cu(II) complexes. Reduction of these Cu(II) complexes into Cu(I) with diazoesters was studied by uv-vis and epr spectroscopy. The enantioselective cyclopropanation reaction was carried out using styrene as a model substrate. 相似文献
95.
Vinod K. Ahluwalia Manjula Khanna Rishi P. Singh 《Monatshefte für Chemie / Chemical Monthly》1983,114(1):71-77
Condensation of orcinol with 2-methylbuta-1,3-diene (isoprene) has been achieved in the presence of orthophosphoric acid as catalyst leading to the exclusive formation of 2,2-dimethylchromans in one step. A novel route for the synthesis of 5-methylxanthyletin derivatives is described. 相似文献
96.
The copolymers, poly(methyl methacrylate-co-methyl acrylate) (PMMAMA), poly(methyl methacrylate-co-ethyl acrylate) (PMMAEA) and poly(methyl methacrylate-co-butyl acrylate) (PMMABA), of different compositions were synthesized and characterized. The effect of alkyl acrylate content, alkyl group substituents and solvents on the ultrasonic degradation of these copolymers was studied. A model based on continuous distribution kinetics was used to study the kinetics of degradation. The rate coefficients were obtained by fitting the experimental data with the model. The linear dependence of the rate coefficients on the logarithm of the vapor pressure of the solvent indicated that vapor pressure is the crucial parameter that controls the degradation process. The rate of degradation increases with an increase in the alkyl acrylate content. At any particular copolymer composition, the rate of degradation follows the order: PMMAMA > PMMAEA > PMMABA. It was observed that the degradation rate coefficient varies linearly with the mole percentage of the alkyl acrylate in the copolymer. 相似文献
97.
R.P. Pant Manju Arora Balwinder Kaur Vinod Kumar Ashok Kumar 《Journal of magnetism and magnetic materials》2010,322(22):3688-3691
Nanoparticles of CoGdxFe2−xO4 (where x=0.0, 0.1, 0.3, 0.5) series have been prepared by chemical co-precipitation. The effect of Gd3+ ion concentration on crystalline phase, crystallinity, crystallite size, molecular vibrations and magnetic resonance has been investigated in detail. The crystallinity decreases with an increase in Gd3+ ion concentration and changes the structural parameters. The spin lattice relaxation has been correlated with the doping ion concentration. Similarly, the superparamagnetic behavior of these particles has been observed with EPR spectroscopy. 相似文献
98.
We prove that a connected topological space with endpoints has exactly two non-cut points and every cut point is a strong cut point; it follows that such a space is a COTS and the only two non-cut points turn out to be endpoints (in each of the two orders) of the COTS. A non-indiscrete connected topological space with exactly two non-cut points and having only finitely many closed points is proved homeomorphic to a finite subspace of the Khalimsky line. Further, it is shown, without assuming any separation axiom, that in a connected and locally connected topological space X, for a, b in X, S[a,b] is compact whenever it is closed. Using this result we show that an H(i) connected and locally connected topological space with exactly two non-cut points is a compact COTS with end points. 相似文献
99.
Vinod Singh Buddhi Vallabh Tripathi 《International Journal of Theoretical Physics》2013,52(2):604-611
Using a two potential approach, dyon solutions have been found in the temporal and non-temporal gauges for a non-Abelian theory. Both the charges, electric and magnetic, of the temporal dyon solution are topological, while for the non-temporal case both charges are partially topological. 相似文献
100.
Vinod D. Gupta Abhinav B. Tathe Vikas S. Padalkar Vikas S. Patil Kiran R. Phatangare Prashant G. Umape Ponnadurai Ramasami Nagaiyan Sekar 《Journal of fluorescence》2013,23(6):1121-1138
Push-pull chromophores attached to carbazole based π-conjugating spacers bearing N-alkylamino donors, cyanovinyl and carbethoxy acceptors have been studied by the means of UV-Visible measurements. The intramolecular charge transfer (ICT) of these π-conjugated systems has also been tested by investigating the ability of the solute molecules to undergo shifts in their fluorescence emission maxima with increasing solvent polarity. Density Functional Theory [B3LYP/6-31G(d)] and Time Dependent Density Functional Theory [TD-B3LYP/6-31G(d)] computations have been used to have more understanding of the structural, molecular, electronic and photophysical parameters of push-pull dyes. The largest wavelength difference between the experimental and computed electronic absorption maxima was 45 nm. For emission, a largest difference of 61 nm was observed. The ground state and excited state dipole moments in different solvents were determined using experimental solvatochromic data and computed Onsager radii. The dipole moments of the molecules in the excited state were observed to be higher than in the ground state. 相似文献