mixture consisting of unreacted 1 and two other germanium compounds. The mass spectrum of the major product (crude yield 50%, HPLC) showed it to contain a skeleton of eight germanium atoms. The X-ray structural analysis"O1 ( Fig. 1) confirmed this, showing that 2 is 4,8-dibromoocta-tert-butyltetracyclo[3.3.0.02~7.03~6]octagermane. Both enantiomers of the chiral molecule are present in pairs in the unit cell. Only four signals, instead of eight, were observed for the tert-butyl protons in the 'H NMR spectruml" of 2, which is in accord with the C, molecular symmetry. Not only does 2 exhibit exceptional thermal stability it is also air and moisture stable. n Br' Br Fig. I. Molecular structure of 2 (H atoms omitted). Selected bond lengths [pm] and angles ["I (standard deviations). The numbers marked with dashes indicate symmetry equivalent atoms.
Enantiomere Polychlorbiphenyle. -Semipraparative Anreicherung durch Fliissigchromatographie Enantiomere Polychlorbiphenyle wurden durch Flussigchromatographie an Triacetylcellulose erstmals angereichcrt. Fur (+)/( -)-1 und (+)/( -)-2 wurden Enantiomerenreinheiten von 55 bis 100% erreicht. Polyhalobiphenyls are persistent environmental pollutants which display various biologic and toxicologic effects I). In particular many polyhalobiphenyls are potent inducers of carcinogen-metabolizing enzymes, e. g. cytochrome P-450. The number and position of the halogen atoms strongly influence the biologic activity which has been investigated intensively during the last ycars because many constitutional isomers could be prepared'). Although some of these are chiral and their racemates have been tested3), information about the activity of the separate enantiomers is unavailable, because, to the best of our knowledge, no enrichment of enantiomeric polyhalobiphenyls has been achieved.Separation via diastereomeric derivatives would require the presence of a reactive group in the biphenyl molecule, which is also true for most chromatographic approaches. Two sorbents have been shown to be efficient for liquid chromatographic (LC) separation of racemates in the absence of reactive groups: triacetyl~ellulose~-~' and (+)-poly(trity1-methacrylate)'). Therefore, we attempted the separation of the biphenyls 1-4') on an analytical column of the latter material. However, photometric detection showed some splitting for 4 only. A bigger column would be desirable in order to exploit this splitting on a larger scale. No splitting (3, 4) and moderate splittings (1, 2) were detected on triacetylcellulose. Since this sorbent is more easily accessible, we tried semipreparative enrichment of the enantiomers of 1 and 2 on a column (30 x 2.5 cm) containing 80 g of this material.Q VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1985 01 70 -204
The enantiomers of the sterically hindered title heterobiaryls 1 and 2 have been investigated for the first time analytically and enriched semi-preparatively by liquid chromatography on triacetyl-and tribenzoylceilulose. The circular dichroism spectra of the enriched enantiomers provide relative configurations which are discussed with respect t o the order of chromatographic elution. Barriers t o rotation about the C-N bond have been determined (104-121 kJ mol-') and are rationalized qualitatively by repulsive interactions in a planar transition state traversed upon partial rotation.Paper 2/04107C
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.