Über 2,4-Difluorzimtsäure

Zusammenfassung Aus 2,4-Difluortoluol wurden nach üblichen Methoden 2,4-Difluorbenzaldehyd und 2,4-Difluorzimtsäure hergestellt.     

Hydrogen in perovskites: Mechanism of solubility, chemical state, effect on electron subsystem, phase transformation

The phenomena of hydrogen/water solubility in YBa₂Cu₃O_7-δ and BaCeO₃ undoped and doped by Y and Nd are considered. New experimental data as well as recently published data have been accumulated to discuss the chemical state of protons, taking into account the fairly strong interaction of the protons with the electron subsystem. Phase transformation of the studied oxides induced by hydrogen/water intercalation were revealed by the investigations of thermal effects, X-ray diffraction, Raman spectroscopy, inelastic neutron scattering and nuclear quadrupole resonance. Paper presented at the 5th Euroconference at Solid Statre Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Intramolekulare diels-alder-reaktionen mit substituierten 1,2,4,5-tetrazinen und 1,2,4-triazinen

1,2,4,5-tetrazines as well as 1,2,4-triazines carrying sidechain dienophiles react in an intramolecular Diels-Alder cycloaddition with inverse electron demand to yield novel bicyclic pyridazines and pyridines.     

The mössbauer effect: A potentially ideal probe into Brownian motion

We calculate the Mössbauer spectrum of nuclei embedded in spheres of radius on the order of 1 μm which are suspended in a liquid. We demonstrate that the Mössbauer effect is an ideal means for testing the deductions based upon a generalized Langevin equation which takes into account the effects of acceleration memory on the force and torque of the liquid on a sphere and for studying, generally, the detailed statistical dynamical behavior of Brownian particles. The spectrum is expressed in terms of an integral over an integrand consisting of standard functions. Experimental desiderata are discussed and a list of sample experimental parameters given.     

A Landau theory of the Peierls-BCS transition

We introduce a Landau type theory of the Peierls instability-superconductor transition involving two complex order parameters. Under a particular inequality condition among expansion parameters, the theory predicts that the superfluid conductivity should vary as $\text{(T?T}{}_{\mathrm{<mtext>c</mtext>}}\text{)}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}$ above the critical region and as $\text{(T}{}^1{}_{\mathrm{<mtext>c</mtext>}}\text{?T)}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}$ below the critical region.     

Octopolar chromophores based on donor- and acceptor-substituted 1,3,5-tris(phenylethynyl)benzenes: impact of meta-conjugation on the molecular and electronic structure by means of spectroscopy and theory

The molecular and electronic structures of a series of all-meta-substituted phenylacetylene mesitylenes peripherally substituted with donor or acceptor (D-A) groups are studied. The impact of meta- and para-substitution patterns is also analyzed by employing Raman and optical spectroscopies in conjunction with theoretical calculations. Outer phenyl rings display a partial quinoid character induced by two different motifs: (i) outer phenyls --> triple bond charge transfer for the cases where these phenyls are substituted with electron-donors; (ii) double electron withdrawing effect in the molecules with the peripheral phenyls substituted with electron acceptors. A moderate tuning of the optical gap is observed in agreement with the partial blockade of pi-electron conjugation exerted by the meta disposition. The orbital structure of the compounds partially preserves that of the mesitylene group showing extra-conjugation due to the addition of the arms, so that conjugation is not entirely obstructed but partially impeded in the ground electronic state (i.e., electron occupied orbitals). As for the excited states, the low-lying energy empty orbitals offer better conditions for full conjugation over the whole molecular scaffold. Interesting optical properties such as overlapping centers along the lowest energy optical excitations and enhanced optical transparency with importance for the application of these materials in optoelectronics have been justified on the basis of the electronic structure. A greater degree of quinoidization, and more allowed pi-electron delocalization, over the entire molecule is recognized in the case of linear phenylacetylenes substituting in para positions the central core.