Zu einem Satz von G. Trautmann über den Rang gewisser kohärenter analytischer Moduln

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Dielectric spectroscopy on aqueous solutions of some zwitterionic amino acids

The complex (electric) permittivity of aqueous solutions of dipolar solutes has been measured as a function of frequency between 1 MHz and 40 GHz. Solutes are the isomers DL-2-aminobutyric acid, DL-3-aminobutyric acid, and 4-aminobutyric acid, and also 6-aminohexanoic acid. The measured dielectric spectra show two dispersion/dielectric loss regions, one due to the orientational diffusion of the solute molecules the other one due to the dielectric relaxation of the solvent water. A relaxation spectral function based on a model of the solutions has been fitted to the measured frequency dependence of the complex permittivity. The values for the electric dipole moment and reorientation time of the zwitterionic part of the solute particles derived by this analysis from the measurements fairly agree with theoretical predictions. Quite remarkably, the dipole moment in solution of 4-aminobutyric acid and 6-aminohexanoic acid up to remarkably high solute concentrations is nearly constant. A noteworthy result for the hydration water of the amino acids is, that its relaxation time is almost independent of the solute dipole moment.     

1,3-Dioxolium-, 1,3-dithiolium- und 1,3-diselenolium-ionen - aromatische strukturen oder durch heteroatome stabilisierte carbeniumionen?

Protonation of the bases 6, 7 and 8 with trifluoroacetic acid was investigated on the basis of ^1–3C-nmr measurements. Two models for the generated ions 1–3 are discussed. A decision is possible in favour of carbenium ions, which are stabilized by adjacent heteroatoms.     

Substituent effects in 13C NMR spectra of 6-endo substituted 9-thiabicyclo[3.3.1]non-2-enes

A number of new 6-endo-X-9-thiabicyclo[3.3.1]non-2-enes have been synthesized (X = cyano, carbimino-methoxy, carbomethoxy, carboxylic acid, aminomethyl, tosylmethyl and methyl). The ¹³C NMR spectre of six of these compounds were measured along with those of several known analogues with X = chloro, hydroxy, hydrogen and deuterium. Assignments were carried out with the aid of hetero (¹³C-¹H) and homo (¹H-¹H) nuclear decoupling techniques. For the compounds with X = H and X = Cl our assignments differ from those published previously and hence result in different values of the substituent-induced chemical shifts (SIS-values) in the 9-thiabicyclo[3.3.1] non-2-ene skeleton.Some of the existing theories regarding SIS-values in multiple substituted cyclic compounds are reviewed and reconsidered in view of the new evidence presented here. Mutual repolarization of the C-hetero atom bonds is proposed as an important factor. In the systems under study in this paper an electron donation of the sulfur atom to the endo C₆-X group is postulated in order to explain the SIS-values on saturated C atoms. The signals of the unsaturated carbons are assigned assuming that electric field effects play a major role.     

Fragmentation and reliable size distributions of large ammonia and water clusters

The interaction of large ammonia and water clusters in the size range from <n> = 10 to 3 400 with electrons is investigated in a reflectron time-of-flight mass spectrometer. The clusters are generated in adiabatic expansions through conical nozzles and are nearly fragmentation free detected by single photon ionization after they have been doped by one sodium atom. For ammonia also the (1+1) resonance enhanced two photon ionization through the state with v = 6 operates similarly. In this way reliable size distributions of the neutral clusters are obtained which are analyzed in terms of a modified scaling law of the Hagena type [Surf. Sci. 106, 101 (1981)]. In contrast, using electron impact ionization, the clusters are strongly fragmented when varying the electron energy between 150 and 1 500 eV. The number of evaporated molecules depends on the cluster size and the energy dependence follows that of the stopping power of the solid material. Therefore we attribute the operating mechanism to that which is also responsible for the electronic sputtering of solid matter. The yields, however, are orders of magnitude larger for clusters than for the solid. This result is a consequence of the finite dimensions of the clusters which cannot accommodate the released energy. Received 21 November 2001