Poised on the brink between a bistable complex and a compound

[reaction: see text] An enmeshed supramolecular complex, based on a semi-dumbbell-shaped component containing an asymmetrically substituted tetrathiafulvalene site and a 1,5-dioxynaphthalene site for encirclement by a cyclobis(paraquat-p-phenylene) ring component and with a "speed bump" in the form of an thiomethyl group situated between the two recognition sites, has been self-assembled. This complex is a mixture in acetone solution of two slowly interconverting [2]pseudorotaxanes, one of which is on the verge of being a [2]rotaxane at room temperature.     

Photochemische Reaktionen. 78. Mitteilung. Anwendung der π → π*-induzierten Cyclisierung von α,β-ungesättigten γ-Dimethoxymethylketonen auf 19-Methoxy- bzw. 19-Dimethoxy-Steroid-enone und -dienone

Irradiation at 254 nm of 19-dimethoxyandrost-4-en-17 β-ol-3-one acetate ( 8 ) afforded the epimeric cyclization products 9 (yield 20%) and 10 (4%). Similar transformations were also achieved with the analogous dimethoxy-enone 24 (→ 25 , 65%), and-dienone 30 (→ 31 , 72%), and with the methoxy-enone 33 (→ 34 , 30%), and-dienone 35 (→ 36 , 17%).     

Photochemical reactions. 145th Communication. Carbonyl vs. epoxyketone photochemistry: Photolysis of 1,2;3,4-diepoxy-2,6,6-trimethyl-1-cyclohexyl methyl ketone

The synthesis and photolysis of the title compound 3 is described. Irradiation (λ > 280 nm, MeCN) of the di-epoxyketone 3 leads predominantly to γ–H abstraction. Cyclization furnishes the cyclobutanols 22 – 24 , while cleavage gives compound 25 , presumably via the allene-oxide intermediate 36 . Further, products 27 and 28 are formed by Norrish fragmentation and by initial cleavage of the C(α)? O bond of the oxirane, respectively. The structures of the products 22 – 25 , 27 , and 28 were assigned on the basis of the spectral data of the photolysis products of the ¹³C-labelled diepoxyketone[6,6-dimethyl-¹³C₂]- 3 and by X-ray analysis of the compounds 24 and 35 , the latter being the p-nitrobenzoate of 22 .     

Note on the topological information content of simple graphs

It is shown that simple graphs gave equal topological information content if their automorphism groups are isomorphic. Further, if the automorphism groups of two graphs are represented by wreath products of which the inner groups are isomorphic, then the two graphs possess equal topological information content. Three graphs which correspond to organic molecules illustrate this finding.Dedicated to Professor Dr.Karl Schlögl on the occasion of his 60th birthday.     

Electrochemical recognition of cations by bis(pyrrolo)tetrathiafulvalene macrocycles

[structure: see text] Tetrathiafulvalene redox-responsive ligands devoid of cis/trans isomerism containing the electroactive bis(pyrrolo[3,4-d])tetrathiafulvalene moiety and polyether subunits have been synthesized. One ligand exhibits high binding affinities for Pb2+ and Ba2+ cations as shown by independent methods (1H NMR, UV-vis spectroscopy, and cyclic voltammetry). The ability of this receptor to electrochemically recognize Pb2+ and Ba2+ is shown by cyclic voltammetry.