Über das asymptotische Verhalten der Lösungen nichthomogener linearer Differenzengleichungen

Ohne Zusammenfassung     

Zur Konstitution des Konhydrins

Ohne Zusammenfassung     

Über die Synthese von berberinartigen Basen aus Verbindungen vom Typus des Tetrahydropapaverins

Ohne Zusammenfassung     

Über Abkömmlinge (insbesondere Ester und Acetylprodukte) der Opiansäure,Brom- und Nitroopiansäure

Ohne ZusammenfassungHerrn Hofrat V. v. Lang sagen wir für die Ausführung der Krystallmessungen besten Dank.     

Al3+, Ca2+, Mg2+, and Li+ in aqueous solution: calculated first-shell anharmonic OH vibrations at 300 K

The anharmonic OH stretching vibrational frequencies, ν(OH), for the first-shell water molecules around the Li(+), Ca(2+), Mg(2+), and Al(3+) ions in dilute aqueous solutions have been calculated based on classical molecular dynamics (MD) simulations and quantum-mechanical (QM) calculations. For Li(+)(aq), Ca(2+)(aq), Mg(2+)(aq), and Al(3+)(aq), our calculated IR frequency shifts, Δν(OH), with respect to the gas-phase water frequency, are about -300, -350, -450, and -750?cm(-1), compared to -290, -290, -420, and -830?cm(-1) from experimental infrared (IR) studies. The agreement is thus quite good, except for the order between Li(+) and Ca(2+). Given that the polarizing field from the Ca(2+) ion ought to be larger than that from Li(+)(aq), our calculated result seems reasonable. Also the absolute OH frequencies agree well with experiment. The method we used is a sequential four-step procedure: QM(electronic) to make a force field+MD simulation+QM(electronic) for point-charge-embedded M(n+) (H(2)O)(y) (second?shell) (H(2)O)(z) (third?shell) clusters+QM(vibrational) to yield the OH spectrum. The many-body Ca(2+)-water force-field presented in this paper is new. IR intensity-weighting of the density-of-states frequency distributions was carried out by means of the squared dipole moment derivatives.     

Use of the Anomeric Carbon-13 Proton One Bond Scalar Coupling Constant as a Tool for Detecting 1,2-Orthoester Formation in Oligosaccharide Synthesis

Abstract

The anomeric ¹J_C,J value has for some time been successfully used for structural elucidation of oligosaccharides. The first recorded spectra on unenriched carbohydrates were published by Bock et al. in 1973 and pointed out that the anomeric ¹J_C,J value could be used for assignment of the anomeric configuration since pyranoses with an axial H-1 have a ¹J_C,J value which is approximately 10 Hz lower than the corresponding value in compounds with an equatorial H-1.^1–3 Their method recording non decoupled ¹³C NMR spectra had the disadvantage of being insensitive and thereby time-consuming. Introduction of INEPT⁴ followed by technical developments, has overcome this disadvantage. Nowadays, with reverse detection techniques, technical skill instead of sensitivity is a limiting factor. In this communication I would like to emphasize that the anomeric ¹J_C,J value can be used for detecting 1,2-orthoester formation as well as for establishing a- or P-configuration.