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Selenium Diimides, Aminoselenanes, l5N N M R , 77Se N M R , Coupling C onstants / ( 77Se15N) Selenium diimides R(NSeN)R [R = 'Bu (la ), 'Oct (1 b)], the eight-membered heterocycle 'BuN(SeSeSe)2N'Bu (2) and the aminoselenanes of the type [R(Cl3Si)N]2Se (4a,b) and [(Me3Si)2N]2Se (5) were studied by multinuclear N M R with emphasis on l5N N M R for detec tion of coupling constants J(77Se15N). The selenium diimides possess the largest values of '/ ( 77Sel5N) observed so far ( la : 158.4 and 163.5 Hz; lb : 158.6 and 162.8 Hz). Com pound lb was found to be much more stable than 1 a, the heterocycle 2 being the m ajor decomposition product of la . The selenium diimides ( la ,b ) react readily with hexachlorodisilane to give the bis[alkyl(trichlorosilyl)amino]selenanes 4a,b. The solid state 13C, 15N, 29Si and 77Se CP/M AS N M R spectra of bis[bis(trimethylsilyl)amino]selenane (5) gave results in accord with the known crystal structure, and there is agreement with the solution state N M R data.

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) are widely distributed in the environment. In this study the accumulation potential of PFOA and PFOS in two fish species with different feeding strategies, i.e. chub (Leuciscus cephalus) and river goby (Gobio gobio) inhabiting a river receiving treated waste waters from a municipal waste water treatment plant, were estimated. PFOS was detected in chub (7-250 microg kg(-1) wet weight) and river goby (70-400 microg kg(-1) wet weight) with bioaccumulation factors (BAFs) of 4600 (liver) and 11,000 (organs). PFOA concentrations in both fish were low and in chub mostly below detection limit.

Environmental ranking of refrigerants is of need in many instances. The aim is to assess the relative environmental hazard posed by 40 refrigerants, including those used in the past, those presently used, and some proposed substitutes. Ranking is based upon ozone depletion potential, global warming potential, and atmospheric lifetime and is achieved by applying the Hasse diagram technique, a mathematical method that allows us to assess order relationships of chemicals. The refrigerants are divided into 13 classes, of which the chlorofluorocarbons, hydrofluorocarbons, hydrochlorofluorocarbons, hydrofluoroethers, and hydrocarbons contain the largest number of single substances. The dominance degree, a method for measuring order relationships among classes, is discussed and applied to the 13 refrigerant classes. The results show that some hydrofluoroethers are as problematic as the hydrofluorocarbons. Hydrocarbons and ammonia are the least problematic refrigerants with respect to the three environmental properties.

The surfactants perfluorooctanoate (PFOA), perfluorooctane sulfonate (PFOS), and derivatives of the latter have emerged as globally distributed persistent environmental contaminants. Methods for their reliable quantitative determination at ppt-levels (ng/L) are needed in order to detect their main sources, to elucidate their environmental fate, and to identify potential sinks. The common method for water analysis involves preconcentration by SPE followed by LC coupled to ESI MS/MS (LC-ESI-MS/ MS). All sample preparation steps must be carefully optimized in order to arrive at reliable quantitative data. Two major aspects are important: (i) during SPE, contaminations may arise from materials containing traces of PFOA/S; (ii) during LC-ESI-MS/ MS, ionization yields are suppressed by matrix components and depend upon the analyte concentrations in the extracts. The levels of PFOA/S in the river Roter Main near Bayreuth have been determined using the optimized method.

In the solid state sulfur bis(trimethylsilylimide) 1 has been shown t o adopt the € / Z configuration by singlecrystal X-ray diffraction (space group P i , triclinic). In solution sulfur bis(sily1imides) R(NSN)R' [R = R' = SiMe, 1 or Si,Me, 2; R = SiMe,, R' = Si,Me, 3 or SiMe,SiMe,(NSN)SiMe,are fluxional at room temperature. Comparison of the 'H. 13C, and, in particular, 15N N M R data indicates that 1 and 2 undergo rapid € / Z c ZIEisomerization even at 173 I<, whereas in the case of 3 and 4 this process is slowed at l o w temperature and the E/Z configuration prevails with the SiMe, group in the E position.Sulfur bis(trimethylsilylimide), S(NSiMe,), 1, has been extensively used as a versatile reagent in sulfur-nitrogen chemistry.' In principle, its structure in solution can be described by any of the three configurations Z / Z , E / E and E/Z (2 = syn, E = anti) which are generally possible for sulfur diimides, S(NR) 2 , bearing iden tical subs ti tuen ts. However, there appears to be conflicting evidence in the literature concerning the structure of 1. Analysis of the IR and Raman spectra3 inferred point group C2, indicating a distorted E/E configuration. In contrast a recent electron-diffraction study came to the conclusion that 1 adopts a distorted Z / Z configuration in the gas phase.4 Both 'H and 14N NMR spectra of 1 in solution show a single resonance signal.' A single signal was also found in the 15N NMR spectrum,6 although the reported S(' 5N) value differed considerably from the S(I4N) value. The conditions for recording the 15N NMR spectrum were probably not correct. All this prompted us to reinvestigate the solution-state NMR spectra of 1 and to compare the data with three other related sulfur diimides 2 (R = R' = Si2Me5),7 3 (R = SiMe,, R' = Si,Me,)7 and 4 [R = SiMe,, R' = SiMe,SiMe,(NSN)SiMe,]. A single-crystal X-ray analysis of 1 was carried out at -160 "C in order to establish its solid-state molecular structure.

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