Surface Charging of Zinc Oxide During XPS Examination

Surface charging of zinc oxide during XPS examination has been studied. The magnitude of the charge is 0.4-0.6 eV at room temperature and decreases at higher temperature to almost zero (nominal 0.1 eV at 300 °C) . Reproducible BE values can only be achieved after correction for this charging. Possible mechanisms are briefly discussed

Regiospecific Synthesis and X-ray Structural Study of Trifluoromethyl Substituted Dibenzosemibullvalene

Preparation of the novel regiospecifically trifluoromethyl substituted dibenzobarrelene 5 and dibenzosemibullvalene 6 is described. Unequivocal proof for the stereostructure of 6 was obtained by its X-ray crystallographic analysis. Geometrical data from X-ray structural analysis showed that the ester carbonyl groups adopt unfavorable conformations for conjugative interactions with respect to the cyclopropane ring involved in the skeleton of 6

Diastereoisomerization and X-ray Crystal Structure of meso-di-(2H-Chromene-2-yl) Ether

It was shown by X-ray crystal structure analysis that di-(2Hchromene- 2-yl)-ether (1) exists in the meso-form, i.e. as (2S, 2\u27R)-1. The Xray structural data indicate, also, that geometries of the two 2H-1-benzopyran parts, of which the skeleton of 1 consists, are not identical, that is the molecule is pseudosymmetrical. The meso-l undergoes thermally induced electrocyclic ring opening and reclosure. Thus, meso-1 equilibrates with enantiomers (2S, 2\u27S)-1 and (2R, 2\u27R)-1, as conf\u27irmed by their lH_ NMR spectra after preparative separation of stereoisomers using liquid chromatography on triacetylcellulose

(1S,2S)-(+)- and (1R,2R)-(–)-1,2-Diphenylcyclopropane from their racemic mixture by liquid chromatography on triacetylcellulose

The title compounds were isolated with 86 and 100% enantiomeric purity, respectively, and characterised by their rotations and c.d.-spectra

Molecular-mechanics calculations of the geometry and racemization energies of an N-aryl-2(1H)-quinolone and N-aryl-4-pyridones

The geometries and energies for ground and possible transition states of the quinolone (1) and pyridones (2)–(4) were calculated by the molecular-mechanics method. The calculated energy differences between ground and the lowest transition state are in good correlation (r = 0.994) with the corresponding experimental racemization energies for interconversion of enantiomers (P) rlhar (M) in (1) – (4). However, the calculated potential energy differences do not correspond to measured differences in Gibbs energies. The fact was tentatively attributed to neglection of the entropy contribution to Gibbs energies

Enantiomers and Barriers to Racemization of Sterically Hindered AT-Aryl- and N-Heteroarylpyrroles

The N-aryl- and N-heteroaryl-2,5-dimethylpyrrole-3-carbaldehydes 2–8 have been synthesized by condensation of hexane-2,5-dione with the appropriate amine and subsequent Vilsmeier-Haack formylation of the pyrrole ring. Diastereomeric association complexes of the racemic pyrrole 8 were studied by pmr chemical shifts and the splittings induced by (+)-1-(9-anthryl)-2,2,2-trifluoroethanol. Enrichment of the enantiomers M and P of 2 and 6 was achieved by liquid chromatography on triacethylcellulose. The barrier to partial rotation about the C-N bond in 6 was determined by thermal racemization and its lower limits in 2 and 8 were estimated