Etude comparative des méthyl-borazines par RMN

A comparative study of borazine ( 0 ) and six methyl borazines ( 1 to 6 ) has been conducted by NMR. It becomes evident that the chemical shift of N? CH₃ protons hardly varies between mono-, di- and tri-N-methyl borazines, whereas this parameter undergoes a strong change (in all 0·21 ppm, to high field) when one passes from N-trimethyl borazine (HB? NCH₃)₃ to hexamethyl borazine (CH₃B? NCH₃)₃ through a gradual substitution on the three boron atoms ( 3, 4, 5 and 6 ). Moreover, a systematic variation of the parameter δ has been found between compounds 3, 4 and 5 for the protons which keep precisely the same immediate environment. A qualitative interpretation of this experimental result is proposed in terms of electronic effects general to the hexagonal planar boron/nitrogen ring which characterises these molecules.     

Induction asymétrique et réaction des α-hydroxy-oximes avec le bromure de phenylmagnésium. Synthéses stéreoselectives d'alcools aziridiniques et d'aza-bicyclo[3.1.0]oxo-2 oxaisothiazolidines-1,2,3

A facile synthesis of aziridine is describe. It is the reaction between Grignard regents and α-hydroxoximes in toluene. The aziridine alchohols are cyclised into 2-oxo-oxathiazolidines. The use of the nuclear Overhauser effect allows the assignment of the relative configurations of these latter compounds and also the configuration of the aziridine alcohols. A proof of the Grignard reagent complex with the alcoolate id given by action of methylmagensium bromide with 2-phenyl 3-methanol azirine. The asymetrie insuction observed is discussed with a transition state involving this complex.     

Sur la structure des alkylcycloarsoxanes (RAsO)α

Organometallic compounds of general formula (RAsO)_α are associated as trimers (R = C₂H₅, C₃H₇, C₄H₉) or even as a tetramer (R = CH₃). Their physicochemical properties show them to be cyclic, the oxygen atoms being located in the bridging position. A “limited” electron delocalization may occur in these rings.     

K+P elastic scattering at 32 GeV/c

Elastic scattering of 32.1 GeV/c K⁺ on protons has been measured in a bubble chamber experiment. Results are presented in the momentum transfer interval 0.06–1.40 GeV² and compared with data at different energies. An effective Regge trajectory is calculated using K⁺p elastic data from 10 to 175 GeV/c.     

Crystal structure of RbOsO3N: A new CsReO4-type compound

Crystals of RbOsO₃N are orthorhombic, space group Pnma, with z = 4, a = 5.571(1), b = 5.794(1), c = 13.735(3), Å. Intensities for 556 independent reflections collected on a four-circle diffractometer were used in the structure determination and the structure was refined to a final R value = 0.046 (R_w = 0.056). The structure consists of OsO₃N discrete tetrahedra linked together by 8-coordinated Rb ions. The oxygen and nitrogen atoms are distributed randomly. RbOsO₃N is the first compound belonging to the CsReO₄-type family for which the complete structure has been determined. This structure can be related to scheelite type but appreciable differences occur in tetrahedra arrangement.     

Study of 19Na at SPIRAL

The excitation function for the elastic-scattering reaction p( ¹⁸Ne, p) ¹⁸Ne was measured with the first radioactive beam from the SPIRAL facility at the GANIL laboratory and with a solid cryogenic hydrogen target. Several broad resonances have been observed, corresponding to new excited states in the unbound nucleus ¹⁹Na. In addition, two-proton emission events have been identified and are discussed.