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Unsaturated Systems (unsaturated + system)
Selected AbstractsChemInform Abstract: Addition of Acetonitrile Anions to Unsaturated Systems under Ultrasonically Dispersed Potassium System.CHEMINFORM, Issue 44 2001Yang Gao Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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] Lewis Acid Mediated Aminobenzannulation Reactions of ,-Ketoalkynes: Synthesis of 1-Aminocarbazoles and 9-Aminopyrido[1,2- a]indolesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2009Diego Facoetti Abstract 2-Acyl- N -propargylindoles 1 and 2-acyl-3-propargylindoles 5 undergo aminobenzannulation reactions with pyrrolidine in the presence of an appropriate Lewis acid to give 9-aminopyrido[1,2- a]indoles 6 and 1-aminocarbazoles 7, respectively. The selection of the appropriate Lewis acid, TiCl4 or GaCl3 for 1 and InCl3 for 5, allows the domino process involving the initial formation of an enamine intermediate, followed by a regioselective 6- exo - dig intramolecular nucleophilic attack of the nucleophilic terminus of the unsaturated system (the ,-carbon of the enamino moiety) to the carbon,carbon triple bond. Moreover, several features concerning the reaction mechanism and the role of both catalysts, in connection with the electronic properties of the reacting alkynes, are reported. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Conjugation of two functional groups through an unsaturated systemJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 1 2006Otto Exner Abstract Energies of 51 1-(E),4-(E)-disubstituted 1,3-butadienes (1), 36 1,4-disubstituted benzenes (2) and 36 (E)-1,2-disubstituted ethenes (3) with dipolar substituents were calculated at the B3LYP/6,311,+,G(d,p) level and evaluated in terms of isodesmic reactions expressing the interaction of substituents through the conjugated system. The energy of interaction reaches up to 40,kJ,mol,1, it is roughly similar in the three series and most regular in the series 1. While its correlation within the framework of dual substituent parameter analysis lacks physical meaning, it is possible to separate the conjugative (resonance) component by subtracting the inductive component with reference to 1,4-disubstituted bicyclo[2.2.2]octanes 4. The conjugative interaction is strongly stabilizing for the combination acceptor,donor and destabilizing for two donors; in these cases it is parallel to changes of geometry as they are predicted by the common resonance equations. Interaction of two acceptors is weak; in addition, there are groups that cannot be classified either as donors or as acceptors. Therefore, one can construct a scale of the resonance ability of donors in conjugation with an acceptor and vice versa, but it is not possible to express the interaction of two donors or of two acceptors on a unified scale for all substituents. The resonance description is certainly appropriate for the typical examples (interaction of NO2 and NH2) but should not be generalized to all possible structures. Copyright © 2005 John Wiley & Sons, Ltd. [source] Modeling high pressure reactivity in unsaturated systems: Application to dimethylacetyleneJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2009C. Mediavilla Abstract A general model is introduced to study pressure-induced reactivity on unsaturated systems in the condensed state. The model is applied here to dimethylacetylene (DMA) in the solid phase II (C/2m) because it has been proposed that two DMA molecules can react to form tetramethyl-cyclobutadiene (TMCBD). The proposed reaction process has been modeled by studying the structural and electronic changes undergone by two DMA molecules as they approach each other preserving the crystal symmetry of phase II. Both monodeterminantal (MP2 and DFT) and multideterminantal (CASSCF and MRMP2) methodologies were used to check the reliability of our model in predicting the reactivity of the system under compression. In all cases, structural results are in agreement with low-temperature diffraction experiments for the solid phase II. Our model indicates that DMA is expected to form the TMCBD dimer at intermolecular distances close to 2 Å. This value is in excellent agreement with previous calculations on the existence of long carbon,carbon bonds. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] Stacking interaction study of trans -resveratrol (trans -3,5,4,-trihydroxystilbene) in solution by Nuclear Magnetic Resonance and Fourier Transform Infrared SpectroscopyMAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2008Claudia Bonechi Abstract Interactions between aromatic rings or other unsaturated systems, including ,-stacking and face-to-edge complexes, are the origin of many phenomena in both organic and biological chemistry. It is well known that these interactions play an important role in the stabilization of the stereo-structure of DNA and the tertiary structure of many proteins. Trans -resveratrol (trans -3,5,4,-trihydroxystilbene, trans -RSV) is a phytoalexin found in Vitis sp. and in many other plants and food products and has received much attention because of its possible positive health benefits. In this work, the ,-stacking interaction of trans -RSV was studied by nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. In particular, the proton chemical shift dependence of the RSV concentration in the range 2 × 10,2 , 1 × 10,5M and temperature were analysed. Moreover, the dynamics of the supramolecular aggregates were studied by nuclear spin relaxation data. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||