Treatment of aromatic hydrocarbons with acetone and manganese(II1) acetate gave rise to arylacetones in yields ranging from 25% with chlorobenzene to 74% with anisole. Cerium(1V) salts were also successfully used as promoters but gave lower yields. The reactions were relatively free of side products except with toluene. Isomer distributions, relative rates, and partial rate factors were determined for acetonylation of anisole, toluene, chlorobenzene, and fluorobenzene. A Hammett plot of the log of the partial rate factors for the manganese(II1) system vs. u-constants gave a slope, p , of -2.4 f 0.3. An isotope effect kH/kD = 3.8 was observed for the manganese(II1)-promoted reaction with acetone-d6, indicating rate-determining proton loss from acetone. The overall mechanism involves formation and attack of acetonyl radicals onto the aromatic hydrocarbon followed by subsequent oxidative deprotonation of the resulting u-radical complex. The acetonyl radical exhibits appreciable electron-deficient character in its substitution behavior with aromatic hydrocarbons.
Visible photoluminescence (PL), optical transmission, and Raman scattering spectra of Si nanocrystals embedded in SiO2 matrix have been studied. Films were deposited by rf magnetron sputtering of compound SiO2/Si targets. Films containing silicon in the form of nanocrystals clusters show intense luminescence at room temperature. Films containing only amorphous Si clusters show little or no PL. Annealing in vacuum or in specific atmosphere leads to strong change of the PL spectrum and its intensity. Results are explained by strong influence of the Si/SiO2 interface state on integral PL emission.
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