Carbon-13 NMR study of some isomeric n-nitroindazole derivatives

The ¹³C NMR spectra of 1,5- and 2,x-dinitroindazoles “x=4-7” and 3-bromo-1,x-dinitroindazoles are recorded and discussed. The data on he 2,x-dinitroindazoles confirm our previous structurea assignment based on ¹H NMR spectroscopy. The ¹³C NMR spectra established that in the novel 3-bromo-1,x-dinitroindazoles the N-nitro group is attached at N-1.     

A dominant electrical defect in GaAs

Several as-grown Bridgman and Czochralski GaAs crystals, with dominant electrical levels from 0.13–0.20 eV below the conduction band, have been studied by the temperature-dependent Hall-effect, spark-source mass spectroscopy, and secondary-ion mass spectroscopy. It is shown that no impurity is of a sufficient concentration to account for these levels, and therefore they are composed of single or multiple defects. The detailed nature of the defects has not yet been established but may involve an As vacancy. It is believed that this is the first time that a dominant electrically active center has been shown to be a pure defect in any as-grown semiconductor.     

Resonance photoconductivity in Fe-doped InP

A photoconductivity peak at 0.44 eV is observed in Fe-doped InP. This peak is attributed to electrons which are optically excited from the Fe²⁺⁵E ground state to vibronic levels of the ⁵T₂ excited state, and thermally excited from there to the conduction band. The lineshape is nearly Gaussian and is well fitted by assuming a vibronic coupling energy of about 0.06 eV in the ⁵T₂ state. In analogy with results in the II–VI compounds this coupling may be dominated by interaction with non-symmetric lattice modes which produce a dynamic Jahn-Teller effect.     

On the nitro group transfer from 2-nitro-4,5,6,7-tetrachloro-2H-benzotriazole and 2-nitro-2H-phenanthro[9,10-d]triazole to secondary amines

The synthesis of 2-nitro-4,5,6,7-tetrachloro-2H-benzotriazole 1 and of 2-nitro-2H-phenanthro[9,10-d]-triazole 2 and their transfer of the nitro group to give 1-nitropyrrolidine 4a and 1-nitromorpholine 4b in high yields when reacted with pyrrolidine or morpholine are reported. The reaction of 1 also gives the pyrrolidinium and morpholinium salts 5a-b of 1 .     

Protected propargylic acetals. Nicholas-Prins cyclization leading to functionalized 2-alkynyl-tetrahydropyrans. Intramolecular trapping by allenes

Dicobalt hexacarbonyl complexes derived from propargylic acetals undergo Lewis acid-mediated Nicholas-Prins cyclization in the presence of homoallylic alcohols. The trapping of the resulting cyclic carbocation enables the synthesis of a series of functionalized tetrahydropyrans. The complexation of the triple bond contributes to the suppression of the side reactions and very significantly increases both the yield and the diastereoselectivity of the reaction. Homoallenic alcohols lead to dienic compounds through proton elimination.     

Pyrazoles VI: The electron-releasing capacity of the pyrazole ring

UV and PMR spectral data and C?O frequencies of some methylpyrazoles containing in the 3-, 4- or 5-position, a formyl-, acetyl- or ethoxycarbonyl group are reported. These data confirm earlier conclusions that, in particular, the 4-pyrazolyl group acts as an electron releasing group. The syntheses of a number of formyl-, acetyl- and ethoxycarbonyl pyrazoles are described. In addition, some 4-dicyanovinyl- and 4-tricyanovinylpyrazoles were investigated.     

A rationale for the large breathing of the porous aluminum terephthalate (MIL-53) upon hydration

Aluminum 1,4-benzenedicarboxylate Al(OH)[O(2)C-C(6)H(4)-CO(2)]. [HO(2)C-C(6)H(4)-CO(2)H](0.70) or MIL-53 as (Al) has been hydrothermally synthesized by heating a mixture of aluminum nitrate, 1,4-benzenedicarboxylic acid, and water, for three days at 220 degrees C. Its 3 D framework is built up of infinite trans chains of corner-sharing AlO(4)(OH)(2) octahedra. The chains are interconnected by the 1,4-benzenedicarboxylate groups, creating 1 D rhombic-shaped tunnels. Disordered 1,4-benzenedicarboxylic acid molecules are trapped inside these tunnels. Their evacuation upon heating, between 275 and 420 degrees C, leads to a nanoporous open-framework (MIL-53 ht (Al) or Al(OH)[O(2)C-C(6)H(4)-CO(2)]) with empty pores of diameter 8.5 A. This solid exhibits a Langmuir surface area of 1590(1) m(2)g(-1) together with a remarkable thermal stability, since it starts to decompose only at 500 degrees C. At room temperature, the solid reversibly absorbs water in its tunnels, causing a very large breathing effect and shrinkage of the pores. Analysis of the hydration process by solid-state NMR ((1)H, (13)C, (27)Al) has clearly indicated that the trapped water molecules interact with the carboxylate groups through hydrogen bonds, but do not affect the hydroxyl species bridging the aluminum atoms. The hydrogen bonds between water and the oxygen atoms of the framework are responsible for the contraction of the rhombic channels. The structures of the three forms have been determined by means of powder X-ray diffraction analysis. Crystal data for MIL-53 as (Al) are as follows: orthorhombic system, Pnma (no. 62), a = 17.129(2), b = 6.628(1), c = 12.182(1) A; for MIL-53 ht (Al), orthorhombic system, Imma (no. 74), a = 6.608(1), b = 16.675(3), c = 12.813(2) A; for MIL-53 lt (Al), monoclinic system, Cc (no. 9), a = 19.513(2), b = 7.612(1), c = 6.576(1) A, beta = 104.24(1) degrees.     

Sels de n-alcoxypyridinium porteurs d'une fonction cetone dans leur chaine alcoxyle: Synthese et reactivite vis-à-vis d'amines secondaires

Reaction of α-bromoisobutyrophenone on pyridine l-oxide and γ and β-picoline l-oxide, in the prosence of silver nitrate, leads to N-alkoxypyridinium and picolinium salts, bearring a keto group on their alkoxyl chain. On treatment with pyrrolidine, these salts, are converted to 4-ω-pyrrolidinobutadienyl-3-isoxzolinols, substituted or not by a methylgroup in their chain. The reaction proceeds according to the PARC-ANRO mechanism(Poton Abstraction, Ring Closure-Addition of a Nucleopile, Ring Opening), as demonstrated by isolation of the bicyclic isoxazolino pyridinium intermediates which result form the first phase of this process, In addition, steric hindrance towards ring opening caused by the methyl group in the adduct derived from β-picoline N-oxide, allow observation of a competiting novel mode of fragmentation alkoxylogous of Katritxky's mode A of decmposition of N0-alkoxypyridinium salts.