E. Kleinpeter

1H NMR spectroscopy as a probe of intermolecular interactions in β-cyclodextrin inclusion compounds

Abstract1H NMR spectroscopy was used to probe the formation of inclusion compounds of permethylated and peracetylated ß-cyclodextrins as host molecules and a variety of electronically very different guest molecules. Complexation, obtained only in water, was estimated quantitatively by means of chemical shift/concentration curves of relevant protons, and the intermolecular forces involved are criticially discussed.

The anomeric effect of the carhoethoxy group in oxygen and sulphur containing heterocycles

The anomeric effect of the carboethoxy substituents and the ring oxygen in 1,3-dioxane- and 1,3-oxathiane-2-carboxylates has been estimated in low polar solvents by including empirical correlation factor α to be 4 kJ/mol. The conformational energies of the 2-carboethoxy substituent fit well the parabolic Zefirov dependence on the solvent dielectric constant in the 1,3-dioxane2-carboxylates. Deviations herefrom in the case of the 1,3-oxathiane-2-carboxylates indicate a second conformational equilibrium involved which is the rotation of the COOR substituent about the exocyclic bond to the heterocyclic ring. Preferred rotamers have been assigned and discussed in terms of special πCO/3d(S) orbital interactions.

Liquid-crystalline behaviour of 2,5-disubstituted 1,3-dioxanes subject to the flexibility of terminal chains

Abstract The liquid-crystalline behaviour of 2,5-disubstituted 1,3-dloxanes with the 5-substltuents -CH 2 CH 2 CH 3 , -OCH 2 CH 3 , -SCH 2 CH 3 has been subjected to the intramolecular flexibility of these substituents, which is increasing in the given series to distort the rod-like arrangement of these species in the mesophase.

2,4,6-Tris(dialkylamino)pyrylium salts and related systems, synthesis and reaction behaviour

Abstract 2,4,6-Tris(dialkylamino)pyrylium salts 9 and 2,6-bis(dialkylamino)pyran-4-ones 11 as well as their thio-analogues 10 , 12 have been prepared by a multi-step route starting with 1,1,5,5-tetrachloro-penta-1,4-dien-3-one ( 1 ). The tris(dialkylamino)-substituted 9 , 10 undergo electrophilic substitution. They are better represented as polymethine-like systems. The 2,6-bis(dialkylamino)-substituted 11 , 12 display a significantly increased donor-reactivity at the carbonyl-oxygen.

The effect of para-substituents on the conformational behaviour of 2-aryl-1,3-Dithianes

Abstract The axial-equatorial equilibrium for 2-aryl-1,3-dithianes is remarkly sensitive to the nature of the substituent on the aromatic ring. The effect is solvent dependent and will be discussed in terms of the anomeric effect.

Intramolecular flexibility of heteroanalogous benzo- and dibenzo-1,5-cyclooctadienes

AbstractThe temperature-variable1H and13C NMR spectra of a series heteroanalogous mono- and dibenzo-1,5-cyclooctadiene derivatives have been obtained, and the present dynamic process discussed in terms of the preferred conformations of the eight-membered ring and the occuring ring interconversional process as well. The boat conformation, which is at − 120 °C still the average of the apparent twist boat conformations, has been identified by dynamic NMR spectroscopy, interconverting via a boat inversional mode. The free energies of activation,

1H NMR lanthanide-induced shift investigation of highly flexible molecules—a new approach

\Delta G_c^{| = }

Zur konformativen Anordnung dipolarer Substituenten in 5-Stellung von 1,3-Dioxanen

, for the latter process have been determined and discussed according to structural variations, the concentration of the samples, present heteroatoms, and solvent influences, respectively. A few chemical shift aspects of more general interest are mentioned.ZusammenfassungDie1H- und13C-NMR-Spektren einer Reihe heteroanaloger Benzo- und Dibenzo-1,5-cyclooctadiene werden berichtet und der bei Temperaturvariation meßbare dynamische Prozeß hinsichtlich Vorzugskonformationen des 8-Ringes bzw. der Art des vorliegenden Ringinversionsprozesses diskutiert. Die Bootkonformation (bei − 120 °C noch ein schnelles Gleichgewicht der entsprechenden Twist-Boot-Konformationen) wird mittels dynamischer NMR-Spektroskopie nachgewiesen und die 8-Ringinversion über einen Bootinversionscyclus realisierend identifiziert. Hierfür meßbare freie Aktivierungsenthalpien,