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The chemistry of the non-metallic elements has in recent years passed through a period of rapid development, often referred to as its "renaissance". To emphasize just one of the key facets: numerous short-lived molecules containing multiple bonds to elements of the third and higher periods have been discovered, often accompanied by the planned synthesis of derivatives which are sterically shielded by bulky groups and thus kinetically stabilized. Thus today molecules such as silabenzenes HhC6-"Sin and silaethenes H2Si=CH2 or R2Si=CR2, disilenes R2Si=SiR2 and diphosphenes RP=PR, silaphenylisonitrile H,C,-N=Si, or methylidyne-phosphanes R-C=P, are all well-known species. Sandwich compounds with P6 rings or silicon centers demonstrate that there are now hardly any barriers to impede the imagination of the nonmetal chemist. In sharp contrast is our lack of knowledge regarding the "microscopic" pathways of chemical reactions: thus apart from information provided for example by molecular beam experiments, or from exact numerical calculations involving species consisting of only a few atoms, it remains largely unknown from which directions medium-sized molecules must approach each other to successfully collide and form a "reaction complex", in which way their structures are changed in such a process or which role is played by molecular dynamics in the energy transfer.-The pyrolysis o f azides X-N,, i.e. compounds which tend to explode violently when ignited in the condensed phase but can be heated in low-pressure gas flow systems without much risk, illustrates that studies of reactive intermediates are of interest not only because novel molecules may be discovered and isolated, and thereby possibilities for synthesis expanded. Moreover, some aspects of the "microscopic" pathways of these a i d e pyrolyses can be described satisfactorily on the basis of calculated energy hypersurfaces, and the influence of molecular dynamics becomes experimentally visible in the "chemical activation" o f intermediates which leads to their "thermal explosion". "Despite all that is known about reaction behavior, understanding of it is rather shallow . . . " (George C . Pimentel"') mhH. 0-6940 Weinhrini, 1987 OS70-083~/87/0606-OS04 S 02.50/0 Angew. Chem. In!. Ed. Engl 26 (1987) 504-526

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Not only steric shielding but also resonance with a delocalized π‐electron system can help to stabilize nonclassical multiple bonds. Thus, despite high steric demands, 15 C atoms and the Ge atom of the title compound 1 lie nearly in the same plane. The experimental finding is in agreement with the result of a MNDO calculation.