Dynamical SAXS investigations on oriented polyethylene by synchrotron radiation: reversible variation of superstructure

Using the synchrotron radiation SAXS facilities at DESY, the reversible variation of the small angle diagram of LDPE during heating and cooling cycles was measured. There are changes of the intensity, location and widths of the small angle reflections. The experimental results and a qualitative discussion are given.     

Origin of the SN2 benzylic effect

The S N2 identity exchange reactions of the fluoride ion with benzyl fluoride and 10 para-substituted derivatives (RC6H 4CH 2F, R = CH3, OH, OCH 3, NH2, F, Cl, CCH, CN, COF, and NO2) have been investigated by both rigorous ab initio methods and carefully calibrated density functional theory. Groundbreaking focal-point computations were executed for the C6H5CH 2F + F (-) and C 6H 5CH2Cl + Cl (-) SN2 reactions at the highest possible levels of electronic structure theory, employing complete basis set (CBS) extrapolations of aug-cc-pV XZ (X = 2-5) Hartree-Fock and MP2 energies, and including higher-order electron correlation via CCSD/aug-cc-pVQZ and CCSD(T)/aug-cc-pVTZ coupled cluster wave functions. Strong linear dependences are found between the computed electrostatic potential at the reaction-center carbon atom and the effective SN2 activation energies within the series of para-substituted benzyl fluorides. An activation strain energy decomposition indicates that the SN2 reactivity of these benzylic compounds is governed by the intrinsic electrostatic interaction between the reacting fragments. The delocalization of nucleophilic charge into the aromatic ring in the SN2 transition states is quite limited and should not be considered the origin of benzylic acceleration of SN2 reactions. Our rigorous focal-point computations validate the benzylic effect by establishing SN2 barriers for (F (-), Cl (-)) identity exchange in (C6H5CH2F, C6H 5CH2Cl) that are lower than those of (CH3F, CH3Cl) by (3.8, 1.6) kcal mol (-1), in order.     

Chelate von β-Dicarbonylverbindungen und ihren Derivaten. 48 Ligandeigenschaften von 1-Phenyl-3-methyl-4-thiobenzoylpyrazolon, -4-benzoylthiopyrazolon und -4-benzoylselenopyrazolon

Chelates of β-Dicarbonyl Compounds and their Derivatives. 48. Properties of the 1-Phenyl-3-methyl-4-thiobenzoylpyrazolone, -4-benzoylthiopyrazolone, and -4-benzoylselenopyrazolone Ligands Thio and seleno derivatives of 1-phenyl-3-methyl-4-benzoyl-pyrazolone were synthesized by reaction of 1-phenyl-3-methyl-pyrazolon with dithiobenzoic ester and by reaction of the analogue 4-benzoyl-5-chlorpyrazole with sodium hydrosulfide or -selenide. Metal chelates of Cu, Ni, Co, Zn, Cd, Hg, Tl, and In were isolated. The influence of the central atoms on the optical behaviour was studied.     

OrdnungszustÄnde und diamagnetische SuszeptibilitÄt in PolyÄthylen

Ohne ZusammenfassungEiner von uns (F. J. B. C.) ist der Alexander-von-Humboldt-Stiftung für ihre Unterstützung wÄhrend dieser Arbeit zu au\erordentlichem Dank verpflichtet. HerrnR. Grewe möchten wir für seine Hilfe bei der Durchführung der Messungen herzlich danken. Herr Dr.H. Knoll hat uns die Benutzung der Magnetwaage am Institut für Anorganische Chemie der FU ermöglicht. Wir möchten ihm ebenfalls unseren Dank aussprechen. Ebenso danken wir der Deutschen Forschungsgemeinsehaft für ihre Unterstützung.