lene and that three ethylene molecules have become bonded to the nickel.

No abstract

Oligoaza derivatives of biphenyl, terphenyl, quaterphenyl, quinquephenyl, sexiphenyl, septiphenyl, octiphenyl, noviphenyl, deciphenyl and dodeciphenyl and poly(pyrimidinylenephenylene) can be synthesized from readily accessible vinamidinium salts and amidines or N,N,N'-tris(trimethylsilyl)amidines. The fluorescence of these systems can be tuned over a wide spectral range by varying number and positions of N atoms. Oligo(diazaphenyls) are thermally and photochemically stable, are easier to reduce than oligophenyls, can be dissolved at any rate in strong acids and show strong blue fluorescence in solution as well as in the solid state.

Amer. Pat. 2533233a [1950]; C. A. 45, 2804 [19Sl]. 95 [1947].

Ebenso wie rnit Arylisocyanaten4-6) la& sich Nitromethan -nach Umwandlung in das Na-Salz rnit Na-Hydrid in Dimethylformamid -auch rnit Phenylsenfol zur Reaktion bringen. Der Versuch, aus dem Na-Salz 5 durch Ansauern Nitro-thioacetanilid in Freiheit zu setzen, scheiterte, da das zunachst gebildete rote 0 1 sich rasch zu einer schwarzen Masse zersetzte. Ohne Schwierigkeiten ist 5 jedoch mit Methyljodid in das Nitroketen-S.N-aceta16 iiberfiihrbar. ' 6Ph-NCB CHZ - Benzoyl-dithioessigester bzw. f3-Hydroxy-dithiozimtsiioreesterAcyl-dithioessigester bzw. die tautomeren Acylketen-halbmercaptale sind bislang nur wenig untersucht worden7-9). Obwohl die Umsetzung des Acetophenons und substituierter Acetophenone rnit Schwefelkohlenstoff mehrfach bearbeitet worden ist 7,9, lo), blieb der Benzoyl-dithioessigsaure-benzylester -in schlechter Ausbeute aus dem Dikaliumsalz der entsprechenden Dithiosaure erhalten7) -die einzige bekannte Benzoylverbindung dieser Reihe. 594Gompper und Schaefer Jahrg. 100

is frequently offset by the disadvantage that they form stable nitrogen addition products, thus forestalling a C reaction. It is often difficult, on the other hand, to find agents of sufficiently high electrophilic potential to react with enol ethers without initiating polymerization. Thus, the two classes of compounds complement each other well in their reactions as derivatives of ketones and aldehydes. C-Substitution reactions with phosgene, oxalyl chloride, and sulfonyl isocyanates, for example, which proceed very smoothly with enol ethers, are impracticable with enamines because of the formation of comparatively stable Nreaction products. Halogenation, and, in general, reactions tending to proceed via free-radical rather than polar mechanisms are also easier to carry out with en01 ethers than with enamines. Since, in addition to the electrophilic and free-radical reactions discussed here, enol ethers may also react with nucleophiles, there is a wide field for their preparative use.We are grateful to the Deutsche Forschungsgerneinschaft and the Fonds der Chemischen Industrie for the support of our work on enol ethers.

The cover picture shows part of a computer-controlled automatic apparatus used for rapid separations of short-lived atomic nuclei by liquid chromatography. A programmable electronic control-unit (shown in the upper half of the picture) schedules the separation procedure. In the center of the picture the position is shown where the products of nuclear-chemical reactions are deposited and dissolved after transportation by a gas-jet. The solution is continuously fed onto either of the two chromatographic columns contained in the metallic heating blocks shown at the bottom of the picture. The flow of different elution media is controlled by pneumatic valves in the red cylinders. Such set-ups are used in the search for superheavy elements. More about the results of these experiments, about the syntheses of the heaviest chemical elements and about the future trends of such studies is reported by G. Herrmann on page 1417ff. (Photo: A. Zschau, GSI Darmstadt) Review ArticlesElements 107, 108, and 109, the three heaviest artificial elements, were prepared by nuclear fusion in the Darmstadt heavy-ion accelerator UNILAC from the heaviest stable atomic nuclei, lead-208 and bismuth-209, and the neutron-richest stable isotopes of chromium and iron. The yields are extremely low; only three atoms of element 109 have so far been observed. All other transuranium elements are also products of nuclear-chemical syntheses. It has not yet been possible to detect the theoretically predicted "superheavy" elements with atomic numbers around 114 and ca. 184 neutrons: while they should be capable of existing, no route for their preparation has yet been devised. Synthesis of the Heaviest Chemical Elements-Results and PerspectivesAromaticity and antiaromaticity have always been a subject of controversy. The donoracceptor concept has afforded new arguments for the understanding of these terms; donor and acceptor substituents in the same molecule stabilize cyclic compounds with (4n) n-electrons (see 1) and destabilize those with (4n + 2) n-electrons (see 2, which does not undergo aromatization). New compounds of this type are of interest, for example, for developments in the area of organic metals and in non-linear optics.

each other is reduced. Indeed, a reduced sliding ability of the molecules, dependent on T,,, and thus an increase in intermolecular cross-linkage is demonstrated by the delayed increase in [?/Ii shown in Figure 2.