β-carboline as a probe for the sonolysis of alcohols and chloromethanes

Sonolysis at 20 and 500 kHz of alcohols, chloromethanes and dilute mixtures of the latter in the former was studied by ultraviolet spectrophotometry in the presence of β-carboline. Acidic degradation products were detected at low frequency sonication, especially for solutions of carbon tetrachloride in alcohols.     

New high-energy luminescence bands from Co2+ in ZnSe

Three sharp absorption features in the energy range 2.36–2.55 eV have been detected in the transmission spectrum of Co-diffused ZnSe, and a number of luminescence transitions originating from the lowest of these states at 2.361 eV have been observed. Photoluminescence excitation spectra prove that these are high energy excited states of the Co²⁺_Zn impurity, a conclusion confirmed by comparison of measured and predicted luminescence energies. This represents the first identification of luminescence branching from a higher excited state of a transition metal ion in any semiconductor. The sharp, weakly phonon-coupled transitions involve either intra-impurity excitation or transitions from the impurity to localised states split off from a minimum in the conduction band. The implications of these observations for the mechanism of host-impurity energy transfer and for the nature of the excited state wavefunctions are discussed.     

Ultrasounds in organic synthesis 31. A simple,high yield modification of the bouveault reaction

Aldehydes are readily obtained in high yield by ultrasonic irradiation of various alkyl and aryl halides in the presence of lithium and DMF.     

The sonochemical arylation of malonic esters mediated by manganese triacetate

The intermolecular arylation of malonate esters in acetic acid solution in the presence of manganese(III) triacetate is known to proceed via an Electron Transfer mechanism. Under sonication, this reaction undergoes only minor changes. In contrast, the intramolecular reaction of dimethyl alpha-(3-phenylpropyl)malonate provides a new case of sonochemical switching, with the formation of compounds 7-9, while conventional thermal conditions generate only the bicyclic compound 6. Reactions using the more powerful oxidant, cerium ammonium nitrate are governed by the formation of the nitrate ester 11. Compounds 7-9 are isolated in yields lower than with MnTA, and in proportions depending on the conditions, thermal or sonochemical.     

Hydrogenic systems,frequency standards and fundamental constants

Hydrogenic (two-body) systems are the only atomic systems for which uncertainties in calculations of the energy levels approach the current state of the art in frequency measurement. This article discusses progress in the theory and measurement of transition frequencies in hydrogenic systems. These studies have relevance to the determination of fundamental constants and the testing of physical theories, especially quantum electrodynamics. A set of high accuracy calculable frequency standards could also be realized by using hydrogenic systems.     

The role of solvent in sonochemical reactions: the case of acetic acid

Among the sonolysis products of acetic acid, oxidizing intermediates can play a direct role in reactions run in this solvent, illustrating the fact that organic sonochemistry can originate in organic solvents as aqueous sonochemistry can in water.     

Ultrasound in organic synthesis 6. An easy preparation of organozinc reagents and their conjugate addition to α-enones

Sonication allows the efficient preparation of various organozinc reagents, which cleanly add in a conjugate fashion to α-enones in the presence of Ni(acac)₂.     

Haloketone dehalogenation by iodide ion

NaI in aqueous acid-THF is an efficient reagent for dehalogenation of α-haloketones.     

Stereochemistry of allenic compounds : Absolute configuration of cycloallenols and cycloallenones

The absolute configuration of α-cycloallenols (3 and 4)as well as of α-cycloallenones(1)has been correlated to that of cyclic alkenols (2) by chemical transformations.