Reinhard Zeisberg

Spektroskopische Untersuchungen : XVIII. Vergleichende 1H−und 13C-NMR-Studie isoelektronischer O-, S-, Se- und Te-arylester aromatischer Carbonsäuren

Abstract The 13 C resonances of the sp 2 hybridized carbon atoms of the isoelectronic substituted O -, S -, Se -, and Te -aryl esters of benzenecarboxylic acids (I–IV) and of the benzenedicarboxylic acid (IX) as well as of the diaryl dichalkogenides V–VII are assigned. The same is done for the aromatic 1 H NMR peaks of compounds III, IV, VI and IX. The influence of the chalkogen atoms on the positions of these NMR signals in all isoelectronic series of compounds is discussed. Furthermore parallels in the effects of the four chalkogenes O, S, Se, and Te in the compounds I–VII and IX as well as the four halogens F, Cl, Br, and I in the 4-halotoluenes VIII on the 1 H and 13 C resonances of the aryl rings directly attached to these elements are described and explained.

Helifulvanolsäkure—ein neues diterpen mit anomalem kohlenstoffgerüst aus Helichrysum fulvum

Abstract The aerial parts of Helichrysum fulvum afforded, in addition to beyerenic acid and ent-kaurenic acid, two new diterpenic acids with the hitherto unknown carbon skeleton of an isotrachylobane type. The structures of these acids, isolated as their methyl esters, were elucidated by extensive NMR studies, some chemical transformations and by X-ray structural analysis of the corresponding acetate. The related alcohol on reaction with pyridinochlorochromate afforded a homoconjugated diene probably formed by fragmentation of a cyclopropyl carbinol. The possible biogenesis of the new carbon skeleton is discussed briefly.