Otto Jarchow

Isolierbare cyclobutadiene, IV. - Reaktionen von singulett- und triplett-sauerstoff mit einem isolierbaren cyclobutadien. Eine dioxetan-dioxetan-umlagerung ☆

Zusammenfassung The reactions of the isolable cyclobutadiene 1 with 3O2 and 1O2 yield the 1,2-dioxetanes 2 and 3 in different ratios. The dioxetane 3 rearranges rapidly in polar solvents to the isomeric dioxetane 2.

Real structure of KInS2 polytypes

Abstract KInS2 crystallizes in a two dimensionally ordered structure, which is related to the TlGaSe2-type structure. High-resolution transmission electron microscopy (HRTEM) and the analysis of diffuse scattering give evidence for defined shifts between ordered layers, which establish a lamellar nanostructure. The different arrangements of the lamellas, designated as A and B are fully compatible with the pseudosymmetry of KInS2. Consequently no misfit of the real structure can be observed by HRTEM. Only in rare cases the arrangement of the layers is at least partially ordered within extended domains and the diffuse scattering narrows into Bragg reflections. Two different strategies for the simulation of the diffuse scattering are presented. Besides the approximation of the diffuse scattering by Bragg intensities which are calculated on the basis of an ordered supercell, the diffuse scattering can also be simulated in dependence of the probability of AB or BA neighbors.

The crystal and molecular structure of threitol

Abstract The structure of threitol, C 4 H 10 O 4 , was determined on a crystal of l -threitol at 293 K. This investigation covers also the racemate, because threitol is one of the rare examples that crystallizes as a conglomerate of the pure enantiomers. In disagreement with a recent publication [Jeffrey and Huang, carbohydr. Res. , 223 (1992) 11–18], the space group of l -threitol is P 3 2 with nine molecules in a unit cell of a = 1755.6(1), c = 487.9(1) pm. Crystals of threitol are found as twins by merohedry with a chemically equivalent molecules. The final conventional R factor is 0.032 for all 3628 symmetry-independent reflections. The molecule have the straight carbon-chain conformation, but do not show C 2 symmetry as was claimed previously. This fact confirmed by solid state 13 C CP/MAS NMR experiments.

Die kristall- und molekülstrukturen von drei thermodynamisch benachteiligten 2,6-anhydronitroalditolen (“Glycopyranosylnitromethanen”)

Abstract In extension of previous work, the crystal structures of three thermodynamically less favoured anhydronitroalditols, two of them as acetylated compounds, i.e. , 2,6-anhydro-7-deoxy-7-nitro- d - glycero - l - gulo -heptitol (“α- d -glucopyranosylnitromethane”), 1,3,4,5-tetra-O-acetyl-2,6-anhydro-7-deoxy-7-nitro- d - glycero - d - manno -heptitol (“α- d -mannopyranosylnitromethane tetraacetate”), and 3,4,5-tri- O -acetyl-2,6-anhydro-1-deoxy-1-nitro- d - ido -hexitol (“α- d -xylopyranosylnitromethane triacetate”), were determined by X-ray diffraction using direct methods. This allowed a comparision of the bond lengths and angles at the anomeric centre of “glycopyranosylnitromethanes” with axial vs. equatorial orientation of the nitromethyl group, which gave evidence for an “anomeric effect” of the nitromethyl group.

Strukturanalyse der methyl-2,3,6-tridesoxy-2-C-[2-hydroxy-1,1-(Äthylendithio)Äthyl]-α-l-threo-hexopyranosid-4-ulo-22,4-pyranose

Abstract Methyl 2,3,6-trideoxy-2- C -[2-hydroxy-1,1-(ethylenedithio)ethyl]-α- l -threo-hexopyranosid-4-ulo-2 2 ,4-pyranose ( 1 ) crystallizes in a rhombic space group P2 1 2 1 2 1 with four molecules in the elementary unit. The structure was refined to an R-value of 0.057. The aldopyranose ring adopts a 1 C 4 conformation with an axial side-chain forming a hemiacetal ring to the keto group at C-4. Both six-membered rings connected in the 2,7-dioxabicyclo[3.3.1]nonane system differ only slightly from the 1 C 4 chair conformation. The spirocyclic dithiolane ring adopts a nearly ideal envelope form with a deviation of C-21 from the plane S-1-C-7ue5f8-S-2-C-22. The dihedral angle O-5-C-1 ue5f8O-1-C-11 of 59.1° is an agreement with the exo-anomeric effect.