Durch Bromierung ausgelöste Umlagerung tertiärer Allylalkohole: Der Einfluss eines Fluor-Substituenten auf Reaktionsgeschwindigkeit und Reaktionsverlauf

Rearrangement of Tertiary Allyl Alcohols Induced by Bromination: The Effect of a Fluorine Substituent on the Rate and the Outcome of the Reaction The allyl alcohol bearing a methyl and a t-butyl group at the hydroxylated position was found to undergo a rearrangement when treated with bromine (or N-bromosuccinimide) in an aqueous medium and to afford a product mixture containing two regioisomeric ketones and one oxirane. Introduction of an additional methyl group or a fluorine atom at the non-terminal olefinic center led to a more selective discrimination between potential migratory groups. As the result of an exclusive t-butyl shift only one product, a ketone, was formed in both cases. Whereas the reaction rate was only slightly affected by the additional methyl group, it was substantially decreased by the fluorine atom.     

Umlagerung von α-Halogen- in α′-Halogen-cyclobutanone,Schlüsselstufe einer variationsreichen Synthese von Pyrethroiden

Rearrangement of α-Halogen- to α′-Halogen-cyclobutanones, Key Step of a Highly Versatile Synthesis of Pyrethroids α-Halogenocyclobutanones, which are readily available by [2 + 2]-cycloaddition of haloketenes to terminal olefins (e. g. 5 → 6 ), undergo an efficient and stereoselective cine-rearrangement to α′-halogenocyclobutanones in the presence of catalysts such as tertiary amines, HX acids or quaternary ammonium salts (e. g. 6 → 7 , Table 1). Preparative as well as mechanistic aspects of the cine-rearrangement are discussed. The 2,4-cis-disubstituted cyclobutanones 7–32 thus formed represent valuable intermediates in a new synthesis of pyrethroids 1 . The X-ray structure of 2-chloro-4-(2,2,2-trichloroethyl)-3,3-dimethylcyclobutanone ( 7 ), the most important precursor of cis- 3 (X = Cl) shows the following features: a puckered cyclobutanone ring (dihedral angle 31°), 2,4-cis-di-pseudoequatorial arrangement of the chloro and trichloroethyl substituents, and an endo-deviation (0.225 Å; 11°) of the carbonyl O-atom from the plane formed by C(1), C(2) and C(4) (Fig. 2).     

Massenspektrometrischer Zerfall und Umlagerung von α-Trifluoracetaminocarbonium-Ionen

α-Trifluoracetamino carbon ions are important fragments in the mass spectra of N-Trifluoracetyl α-amino acids and their derivatives. They fragment by eliminating neutral molecules. This breakdown is mainly influenced by the structure of their substituents. Several of these ions show some remarkable skeletal rearrangements.     

Massenspektrometrischer Zerfall und Umlagerung von α-substituierten N-Methyl-benzylamiden

As a result of high resolution mass measurements, calculation of metastable ions, and investigation of specifically deuterated compounds the fragmentation is discussed of some α-substituted N-methyl benzylamides containing different N-acyl groups. α-Cleavage leads to the formation of N-methyl α-acylamino carbon ions which show skeletal rearrangement. The intensity of the rearranged ions depends on the structure of the N-acyl group. Migration of the α-methyl group is observed in the mass spectra of N-acetyl and N-p-Cl-benzoyl N-methyl-α-phenylethylamide.     

α–γ transition in nylon 6

The α to γ transition that occurs in nylon 6 upon iodine treatment was investigated by infrared spectroscopy, differential thermal analysis, and x-ray diffraction techniques. Thin films of nylon (0.2 mil) were treated in either iodine–potassium iodide aqueous solution or in iodine vapor. Very short treatment times, in the order of 30 sec, were found to effect the transition when a solution 0.5M with respect to iodine was used. The infrared spectra of the iodine nylon complexes formed from either the α- or γ-nylon 6 treated in vapor or dissolved iodine were all similar. This is an indication that molecular iodine is the active species in forming the complex. The temperature of the washing solution used to remove the iodine from the nylon determines whether an α-nylon 6 or γ-nylon 6 is obtained from the complex after washing. Nylon 6 plaque surfaces and thin films are similar in their behavior towards the iodine treatment. The γ-nylon 6 is a stable modification at all temperatures below its melting point. The conversion of the γ form back to the α modification can occur only if the hydrogen bonding is severely affected, e.g., by phenol treatment, iodine treatment, melting, etc. Infrared spectroscopy provided no evidence for an α–γ transition in nylon 6 on heating the sample continuously through its melting point. The shapes of the melting peaks in the above two modifications of nylon 6 were sufficiently different to provide a means of identifying the two crystalline forms.     

Neues über Oxouranate: Über α-Li6UO6. Mit einer Bemerkung über β-Li6UO6

New Investigations about Oxo Uranates: On α-Li₆UO₆. With a Remark about β-Li₆UO₆ The crystal structure of transparent, bright yellow single crystals of α-Li₆UO₆ has been determined. [a = 838.07(5), c = 738.34(7) pm; d_pyk = 4.02, d_x = 4.17 g · cm^?3; space group R3 ; Z = 3; R = 3.17%, R_w = 3.06%; 408 symmetry independent I₀(hkl); AgKα fourcircle diffractometer Philips PW 1100]. The structure is dominated by a threedimensional framwork of “hollow spaces”, built up by 12 O^2? (and 12 Li⁺). The Madelung Part of Lattice Energy, MAPLE, is calculated and discussed.