Andreas Merz

Stereochemistry of the Addition of Bromine to Acenaphthylene Derivatives: Substituent and Solvent Effects

Summary.u2002Addition of bromine to acenaphthylene and 5-bromoacenaphthylene in aprotic solvents of different polarity is not stereospecific: both trans and cis isomers of the corresponding 1,2-dibromides are formed. In general, the relative proportion of syn addition increases with decreasing solvent polarity; the highest percentage of cis products is observed in 1,4-dioxane. The stereochemistry of bromine addition to nine additional 3-, 5-, and 5,6-substituted acenaphthylenes in dioxane is reported. A number of new cis-1,2-dibromoacenaphthenes have been isolated for the first time.Zusammenfassung.u2002Die Addition von Brom an Acenaphthylen und 5-Bromacenaphthylen erfolgt in aprotischen Lösungsmitteln unterschiedlicher Polarität unspezifisch: sowohl cis- als auch trans-Produkte werden gebildet. Allgemein steigt der Anteil der syn-Addition mit steigender Polarität des Lösungsmittels, wobei der stärkste Effekt bei 1,4-Dioxan beobachtet wird. Die Stereochemie der Bromaddition an neun weitere 3-, 5- und 5,6-Acenaphthylenderivate wird beschrieben; einige cis-1,2-Dibromacenaphthenderivate wurden erstmals erhalten.

Conformers and rotamers of (±)-trans-2,3-bis(2-naphthyl)-15-crown-5 and -18-crown-6 and their alkali metal complexes

The conformations of (±)-trans-2,3-Bis(1-naphthyl)-15-crown-5 (1) and -18-crown-6 (2) are investigated by MM2 and dynamic 1H-NMR spectroscopy. The most stable conformation is the diequatorial one in both the free ligands and the alkali metal complexes 1 · NaClO4 and 2 · KClO4. Three rotamers, pseudo-aa, pseudo-ee, and pseudo-ae, with respect to the spatial arrangement of the naphthyl groups, were found as calculated minima by MM2 and experimentally by low-temperature NMR, with fair agreement of the rotational barriers. In the cation-reinforced crowns the rotation rates are significantly diminished. The distribution of the rotamers depends on the size of the crown and its state, free or complexed.