Systematische untersuchungen über das verhalten von organozinn-verbindungen gegenüber flüssigem schwefeldioxid VI. Zum mechanismus der SO2-einschiebung in die zinn—kohlenstoff-bindung

SO₂-insertion reactions of tetraorganostannanes in liquid sulphur dioxide proceed through an open transition state. Arguments favouring an S_E2 mechanism are presented on the basis of investigations on tetraalkyl-, tetraaryl-, and tetraalkenyl-stannanes, mixed substituted and perfluorinated tetraorganotin compounds as well as organotin halides.     

Pfaffsche Formen auf komplexen Räumen

Ohne Zusammenfassung     

Regioselective formation of alkylidenecyclopropanes from 2-substituted cyclobutylidenes generated from geminal dibromocyclobutanes and methyllithium

Four different 2-substituted geminal dibromocyclobutanes were reacted with methyllithium at -78 degrees C. In contrast to previous studies using diazocyclobutanes as carbene precursors at temperatures above 200 degrees C via reaction of the corresponding tosylhydrazone sodium salts, the organometallic route in each case produces only an alkylidenecyclopropane that could be isolated in good yields. B3LYP calculations were employed to rationalize the observed regioselective ring contraction of the generated cyclobutyliden(oid)s. [reaction: see text]     

Application of the revised EU criteria for the confirmation of anabolic steroids in meat using GC-MS

The EU criteria for the confirmation of the presence of illegal compounds in biological matrices were recently revised. The old and the revised criteria were applied to relative ion intensities obtained for five anabolic steroids (methylboldenone, methyltestosterone, ethynylestradiol, -boldenone and -nortestosterone) in meat (cow, pig, turkey) and fish at concentrations ranging from 0.5 to 5.0 g/kg. Confirmatory analysis was done by GC-MS; therefore four diagnostic ions had to be monitored and three ion ratios had to be calculated and tested against the criteria. Application of the old and revised criteria, with either standards or fortified samples as reference, showed mutually rather divergent results. Confirmation according to the revised EU criteria and using fortified samples as a reference gave the best results; in other words the highest percentage of diagnostic ion ratios within the tolerance intervals. A correlation was found between the percentage of these ion ratios and the signal/noise (S/N) ratio of the least intense ion of interest in the recorded MS spectrum. Although there were distinct differences in the results obtained for different analytes and sample types, it is safe to conclude that at S/N=3 the percentage of ratios within the tolerance intervals generally will be at or below 50%, while for S/N10, the percentage increases to over 90%. In the present study, fully satisfactory results were obtained down to about 2 g/kg, but not for lower analyte concentrations.