Isokinetic Relationships in Alcohol Oxidation with Chromic Acid

The activation parameters for the oxidation of 13 secondary alcohols with chromic acid have been determined. Application of a statistical treatment of Exner [9] shows that the reactions are isoentropic with an average entropy of activation (ΔS^≠) of ?24.0 e. u.     

Nitroxydes 91 : β-Cétoénolates nitroxydes

β-Ketoaldehyde derivatives of simple piperidine and pyrrolidine nitroxides as spin labelled ligands give paramagnetic three-electron copper complexes.     

Erratum

Peculiar transitions in the optical spectra of Mn atoms isolated in argon matrices confirm the existence of Mn₂ molecule. The temperature variation of the absorption and MCD intensity in the range 13-27 K demonstrate that the Mn₂ molecule is antiferromagnetic and allows a precise determination of its ground-state exchange energy: J = ?10.3 ± 0.6 cm^?1.     

The Helmholtz equation with impedance in a half-space

In this Note we obtain existence and uniqueness results for the Helmholtz equation in the half-space ${\mathbb{R}}_{+}^3$ with an impedance or Robin boundary condition. Basically, we follow the procedure we have already used in the bi-dimensional case (the half-plane). Thus, we compute the associated Green's function with the help of a double Fourier transform and we analyze its far field in order to obtain radiation conditions that allow us to prove the uniqueness of an outgoing solution. Again, these radiation conditions are somewhat unusual due to the appearance of a surface wave guided by the boundary. An integral representation of the solution is presented by means of the Green's function and the boundary data. To cite this article: M. Durán et al., C. R. Acad. Sci. Paris, Ser. I 341 (2005).