Search results for "force"
showing 10 items of 3423 documents
Syntheses, crystal structures and magnetic properties of one- and two-dimensional pap-containing copper(II) complexes (pap = pyrazino[2,3- f ][4,7]…
2001
Three polynuclear complexes containing copper(II) and pyrazino[2,3-f][4,7]phenanthroline (pap) as the basic building blocks have been prepared [Cu2(pap)(H2O)2(NO3)3]n[NO3]n1, [Cu4(pap)4Cl7]nCln·15nH2O 2, and [Cu4(pap)4(H2O)4(C4O4)2]n[C4O4]n[NO3]2n·12nH2O 3, and their crystal structures and variable-temperature magnetic susceptibilities determined. Compound 1 is a single stranded zigzag chain where pap and nitrate alternate as bridges between the copper atoms. The copper coordination geometry is to a first approximation distorted square pyramidal, but with an additional semi-coordinated oxygen from non-bridging nitrate groups. The bridging nitrate coordinates in the apical position to both c…
ChemInform Abstract: Gold-Catalyzed Intramolecular Hydroamination of o-Alkynylbenzyl Carbamates: A Route to Chiral Fluorinated Isoindoline and Isoqui…
2013
Title compounds are prepared in enantiomerically pure form by the diastereoselective addition of fluorinated nucleophiles to N-(tert-butanesulfinyl)imines (I) followed by a sequence of Sonogashira cross-coupling/gold(I)-catalyzed cycloisomerization of the corresponding carbamate.
WHY DIELS-ALDER REACTIONS ARE NON-CONCERTED PROCESSES
2014
ABSTRACT Two exhaustive topological analyses using the Electron Localisation Function (ELF) along the non-polar Diels-Alder reactions of 1,3-butadiene [J. Phys. Chem. A 107 , 6014 (2003)] and cyclopentadiene [Org. Biomol. Chem. 8 , 5495, (2010)] with ethylene established that the bonding changes along these reactions are non-concerted. Herein, the ELF bonding changes along the intramolecular Diels-Alder reaction of 1-( hex-5-enyl)cyclohexa-1,3-diene is analysed. The geometrical restrictions imposed by the tether break the synchronicity in the single bond formation in this non-polar reaction. The present ELF topological analysis along this intramolecular Diels-Alder reaction supports the ear…
Substituent and temperature controlled tautomerism: Multinuclear magnetic resonance, X-ray, and theoretical studies on 2-phenacylquinolines
2000
Proton-transfer equilibria in chloroform solution of twelve 2-phenacylquinolines were studied by 1H, 13C and 15N NMR spectroscopies. The (Z)-enaminone form stabilized by an intramolecular hydrogen bond was found to prevail in all cases. Electron-donating substituents in the phenacyl part of the molecule lead to an increase of the ketimine form (to 33% for p-NMe2). Variable temperature 1H NMR measurements show that higher temperatures have the same effect. The negative logarithm values of the equilibrium constant, pKT, were found to be linearly dependent on Hammett σ substituent constants. The pKTvs. temperature correlation also has a linear character. In general, strong electron-withdrawing…
Photoinduced switching of electrical properties in thin films of polar indandione type organic molecules
2006
The optically induced switching of organic materials with large dipole moments consisting of acceptor and donor groups bridged by a delocalized π-electron system is important for investigations of optoelectronic effects. To the contrary of azobenzene molecule, photoinduced change of dipole moment of indandione molecule does not need free volume in thin films. To modify the dipole moment and also to optimise properties of film formation, a number of novel indandione derivatives is investigated. Reversible switching of the surface potential of polymer films with incorporated or chemically attached indandione molecules is observed at irradiation in photoinduced intramolecular electron transfer…
A dft study of the regioselectivity in intramolecular diels-alder reactions with formation of a tricyclodecane skeleton
2011
Three different intramolecular Diels-Alder (IMDA) reactions associated with the formation of fused and bridged tricyclodecane skeletons have been studied at the B3LYP/6-31G(d) computational level. While substitution on the diene and dienophile fragments modulates the polar character of the reaction, the strain effect produced by the methylene tether affects the activation energy, and its torsion controls the different regioisomeric channels of the IMDA process. Analysis of the reactivity indices recently proposed (J. Soto-Delgado et al., Org. Biomol. Chem., 2010, 8, 3678) within the conceptual density functional theory allows for the characterization of the mechanism including the charge tr…
ChemInform Abstract: Enantiocontrol in the Intermolecular Cyclopropanation Reaction Catalyzed by Dirhodium(II) Complexes with ortho-Metalated Aryl Ph…
2010
(P) and (M) dirhodium(II) complexes with ortho-metalated aryl phosphines are assessed as chiral catalysts in the enantioselective cyclopropanation of styrenes by ethyl diazoacetate; enantioselectivities up to 91% and up to 87%, respectively, for cis- and trans-2-arylcyclopropanecarboxylates are observed.
2,3,4,5,6-Pentabromophenyl phenyl ether
2002
The title compound, C12H5Br5O, belongs to a group of flame retardants known as polybrominated diphenyl ethers (PBDE). Salient features of the packing are stabilization due to intermolecular Br⋯Br contacts in the ab plane and aromatic intermolecular contacts along the c direction.
Hierarchical halogen bonding induces polymorphism
2009
Co-crystals of 1-iodo-3,5-dinitrobenzene and 1,4-diazabicyclo[2.2.2]octane manifest either two strong or one strong and one weak intermolecular 2 : 1 halogen bond (XB) motifs in polymorphic structures I and II, respectively, whereas weaker XB-donor 4,4-bipyridine just forms 1 : 1 structure III with one strong halogen bond.
Synthese von 2-alkoxysubstituierten Oligo- und Poly(1,4-phenylenethenylen)en und 2-Arylbenzo[b]furanen mit Hilfe der Siegrist-Reaktion
1994
Synthesis of 2-Alkoxy Substituted Oligo- and Poly(1,4-phenyleneethylene)s and 2-Arylbenzo[b]furanes by Applying the Siegrist Reaction Alkylation of 2-hydroxy-4-methylbenzaldehyde (1) yields the 2-alkoxy-4-methylbenzaldehydes (2a-l) which can be easily transformed to the Schiff bases 3a-l. The intermolecular self-condensation in a strongly alkaline medium leads to the oligo- and poly(1,4-phenyleneethenylene)s (4a-i) with an outstanding regular constitution and overall (E)-configuration. The terminal N-arylamino group can be cleaved by hydrolysis generating the compounds 5a-i. An intramolecular condensation forming the benzo[b]furanes 6j,k is observed for 3j,k – due to the activated OCH2 grou…