During irradiation of trimethyl@-toly1)silane l b with (CF3C02),Hg in CF,C02H, an EPR spectrum due to lb" is observed. The spin density in the transient radical cation resembles that of lb-. In contrast to this, the analogous germane 3b gives the radical cation of p-bitolyl. After irradiation of tetrakis-(p-methoxypheny1)silane 2d, the radical cation 2d' + is identified by ENDOR. However, the radical cation of p-bi( methoxyphenyl) is formed with p-met hoxyphenyl( trimethy1)silane 1 d and tetrakisb-methoxy-pheny1)germane 4.The reaction of phenyl-silanes and -germanes la, 4a, 5a with AlC13 in CH2C12 or CHC12CH3 yields the radical cations of anthracene, I, or 9,1O-dimethylanthracene, II. Treatment ofpara-substituted phenyl-silanes, -germanes and -digermanes 1-5 with AlCl, in CH2C12 leads to 2,6-disubstituted, and with A1Cl3 in CHC12CH3 to 2,6,9,1O-tetrasubstituted, anthracene radical cations In-VII. The first step of the reaction is an electrophilic @so-substitution of the silyl or germyl residue followed by a condensation and an oxidation. With hexamesityldigermane 5e, intermolecular methyl transfer takes place to give the radical cations of

: Laboratory experiments on microbial decomposition and on the contribution of diplopods to organic matter decomposition in soil were combined with field studies to reveal the major points of heavy metal effects on the leaf litter decomposition process. The study focused on the accumulation of organic litter material in heavy metal-contaminated soils. Microbial decomposition of freshly fallen leaves remained quantitatively unaffected by artificial lead contamination (1000 mg kg(-1)). The same was true for further decomposed leaf litter material, provided that the breakdown of this material was not influenced by faunal components. Although nutrient absorption in diplopods is affected by high lead contents in the food, this effect alone, however, was shown not to be sufficient for the massive deceleration of the decomposition process under heavy metal influence which could not only be observed in the field but occurred in microcosm studies as well. Reduced reproduction and lower activity of the diplopods most likely were responsible for the observation that lead-influenced diplopods enhanced microbial activity in soil only in a lesser degree than uncontaminated animals did. This effect is assigned to represent the main reason for decreased decomposition rates and the subsequent accumulation of organic material in heavy metal-contaminated soils.

No abstract