Photochemistry of 2-alkoxymethyl-5-methylphenacyl chloride and benzoate

Irradiation of 2-(alkoxymethyl)-5-methyl-alpha-chloroacetophenones (1a-c) and 2-(methoxymethyl)-5-methylphenacyl benzoate (1d) in dry, nonnucleophilic solvents afforded 3-alkoxy-6-methylindan-1-ones (3a-c) in very high chemical yields. 3-Methylisobenzofuran-1(3H)-one (2) was, however, isolated as a major photoproduct in the presence of trace amounts of water. Quenching experiments and laser flash spectroscopy revealed that the indanone derivatives 3 are formed by 1,5-hydrogen migration from the lowest triplet excited state of the acetophenones 1 and cyclization of the resulting photoenols. In contrast, production of the lactone 2 in wet solvents was found to result from two consecutive photochemical transformations. The photoenols produced by photolysis of 1a-c add water as a nucleophile to form 2-acetyl-4-methylbenzaldehyde (4), which is further converted to 2 via a second, singlet state photoenolization process. Exhaustive photolysis of 1a in methanol produced the acetal 2-(dimethoxymethyl)-5-methylacetophenone (7a) as the exclusive product. The remarkable selectivity of these photoreactions may well be useful in synthetic organic chemistry.     

Structural and Magnetic Characteristics of Nanogranular Co–Al2O3 Single- and Multilayer Films Formed by the Solid-State Synthesis

The results of structural and magnetic investigations of nanogranular Co–Al₂O₃ films formed from Co₃O₄/Al thin-film layered structures upon vacuum annealing are reported. The Co₃O₄/Al films have been obtained by sequential reactive magnetron sputtering of a metallic cobalt target in a medium consisting of the Ar + O₂ gas mixture and magnetron sputtering of an aluminum target in the pure argon atmosphere. It is shown that such a technique makes it possible to obtain nanogranular Co–Al₂O₃ single- and multilayer thin films with a well-controlled size of magnetic grains and their distribution over the film thickness.

     

Average orientation of a molecular rotor embedded in a Langmuir-Blodgett monolayer

A molecular rotor in which a naphthalene rotator is attached through a silicon atom to three fatty acid chains has been synthesized, and Langmuir-Blodgett techniques were used to deposit on silica surfaces monolayers of its calcium salt, both neat and diluted with stearic acid salts. The monolayer films have been characterized by ellipsometry and Fourier transform infrared (FT-IR) grazing-incidence attenuated total internal reflection (GATR) spectroscopy on Si-SiO(2) and by UV-vis absorption spectroscopy on SiO(2). The measurements were combined with calculations of the electronic (INDO/S) and vibrational (DFT) transition moment directions to deduce the average orientation of the rotor molecules, including the naphthalene ring, relative to the surface. In both neat and mixed films, the naphthalene ring is found to preferentially tilt toward the surface, enough that its rotation is most likely hindered. A comparable picture was obtained from molecular mechanics calculations on a mixed film of the naphthalene rotor and stearic acid.     

Band gap and type of optical transitions at the interband absorption edge in solid solutions based on bismuth telluride

The spectra of optical absorption in multicomponent n- and p-type solid solutions based on bismuth and antimony chalcogenides with substitutions in both sublattices of Bi₂Te₃ have been investigated. It has been found that, in all the solid solutions studied, just as in the parent compound Bi₂Te₃, direct allowed transitions occur at the interband absorption edge at T = 300 K. The band gap E _g in the n-Bi_{2 ? x} Sb _x Te_{3 ? y ? z} Se _y S _z solid solutions weakly increases with increasing number of substituted atoms in the Bi and Te sublattices. These atomic substitutions do not leads to an increase in E _g as compared to that of the n-Bi₂Te_2.7Se_0.3 composition. An analysis of the optical absorption spectra suggests that the solid solutions under consideration are weakly degenerate, a conclusion supported by the earlier studies of the thermoelectric and galvanomagnetic properties. It has been established that, in the conduction band of the Bi_1.8Sb_0.2Te_2.7Se_0.15S_0.15 solid solution, there is an additional extremum lying above the main extremum at a distance no more than 0.1 eV.     

Suppressing ringing caused by large photomultiplier tube signals

We describe here the characteristic features of the ringing we observed following large PMT signals in the Daya Bay reactor antineutrino experiment. We conclude that the ceramic capacitors used in the circuitry of the PMT bases and the HV-signal decouplers are the primary cause for this ringing. We present some possible schemes to reduce the ringing when replacing these ceramic capacitors is not feasible.     

An efficient palladium-benzimidazolyl phosphine complex for the Suzuki-Miyaura coupling of aryl mesylates: facile ligand synthesis and metal complex characterization

A new class of easily accessible hemilabile benzimidazolyl phosphine ligands has been developed. The ligand skeleton is prepared from commercially available and inexpensive o-phenylenediamine and 2-bromobenzoic acid. With catalyst loading down to 0.5 mol% palladium, excellent catalytic activity towards the Suzuki-Miyaura coupling of aryl mesylates is still observed. This represents the lowest catalyst loading achieved so far for this reaction in general. X-Ray crystallography shows that new ligand L2 is coordinated with Pd in a κ(2)-P,N fashion.     

3-(α-Nitroalkyl- and α-polynitroalkyl-ONN-azoxy)-4-nitraminofurazans and some their derivatives

Methods for the preparation of 3-(α-nitroalkyl- and α-polynitroalkyl-ONN-azoxy)-4-nitraminofurazans with primary and secondary nitramine groups and their derivatives, including N,N′-bis[(3-(α-polynitromethyl-ONN-azoxy)furazan-4-yl]alkylen-N,N′-dinitramines, have been elaborated.     

3,4-Bis(α-nitroalkyl-ONN-azoxy)furazans and some of their derivatives

Reaction of pseudonitroles and their derivatives with diaminofurazan in the presence of dibromoisocyanuric acid (DBI) resulted in symmetrical 3,4-bis(-nitroalkyl-ONN-azoxy)-furazans or their derivatives. For the synthesis of bis(nitroalkyl-ONN-azoxy)furazans bearing various a-nitroalkyl-ONN-azoxy groups, the method based on the reaction of ??-nitronitroso compounds with 3-amino-4-(nitroalkyl)-ONN-azoxy)furazans (in the presence of DBI) was developed. Synthetic procedures towards aforementioned compounds with nitromethyl-, dibromonitromethyl-, trinitromethyl-ONN-azoxy and other groups were described.     

Synthesis of monoazacrown ethers under phase-transfer catalysis

A procedure has been proposed for the synthesis of monoazacrown ethers by reaction of N-benzyldiethanolamine with oligo(ethylene glycol) bis-p-toluenesulfonates in a two-phase system aromatic hydrocarbon-50% aqueous alkali, followed by removal of the benzyl group by catalytic hydrogenolysis. The maximal yields of N-benzylaza-12-crown-4, -18-crown-6, and -21-crown-7 were achieved by adding 4?C10 equiv of LiCl, BaBr₂, and CsCl, respectively, to the reaction mixture, which probably indicated template effect.     

Synthesis and properties of new fluorenonocrownophanes having a stilbene fragment and their reaction with paraquat

New crownophanes containing 2,7-dioxyfluorenone and 4,4??-dioxystilbene fragments linked through di-, three, tetra-, and pentaethylene glycol linkers were synthesized. The formation of pseudorotaxanetype host-guest complexes in reactions of these crownophanes with 1,1??-dimethyl-4,4??-bipyridinium dication was detected by fast atom bombardment mass spectrometry, ¹H NMR, and electron spectroscopy.