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86.
Delphine Josien‐Lefebvre Guillaume Desmares ClaudeLe Drian 《Helvetica chimica acta》2001,84(4):890-897
The total synthesis of the naturally occurring cyanoglucoside (−)‐bauhinin ( 1 ) was achieved starting from the optically pure oxatrinorbornenone 2 in 12 steps and 8% overall yield. The aglycone of (−)‐bauhinin was easily obtained from the optically pure oxatrinorbornenone derivative 6 by a Wittig‐Horner reaction followed by the opening of the oxa bridge. Glycosidation with tetra‐O‐isobutyryl‐D ‐glucosyl bromide 9 as the reagent in the Koenigs‐Knorr reaction afforded glucoside 10 in 58% yield, which, after photoisomerization and deprotection, gave (−)‐bauhinin ( 1 ). 相似文献
87.
Silica supported heteropoly acids are active in n-hexane cracking, while the pure compounds (except H3PW12O40) are inactive. This result is explained by a partial transformation of H6P2W18O62 and H6P2W21O71 (H2O)3 into H3PW12O40. In the case of H4SiW12O40, the polyanion in interaction with silica leads to superacidic species upon thermal treatment.
, , -, ( H3PW12O40) . H6P2W18O62 H6P2W21O71 (H2O)3 H3PW12O40. H4SiW12O40 , , .相似文献
88.
The catalytic activity of three heteropoly acids has been studied in n-hexane cracking. Only H4SiW12O40 does not decompose into oxides at the reaction temperature. Its acidic form is active in cracking but its dehydration leads to an inactive compound.
-. H4SiW12O40 . , .相似文献
89.
Riadh Kefi Erwann Jeanneau Frederic Lefebvre Cherif Ben Nasr 《Structural chemistry》2007,18(6):923-929
Chemical preparation, crystal structure, and NMR spectroscopy of a new trans-2,5-dimethylpiperazinium monophosphate are given. This new compound crystallizes in the triclinic system, with the space group P-1 and the following parameters: a = 6.5033(3), b = 7.6942(4), c = 8.1473(5) Å, α = 114.997(3), β = 92.341(3), γ = 113.136(3), V = 329.14(3) Å3, Z = 1, and Dx = 1.565 g cm?3. The crystal structure has been determined and refined to R = 0.030 and R w(F 2) = 0.032 using 1558 independent reflections. The structure can be described as infinite [H2PO4] n n? chains with (C6H16N2)2+ organic cations anchored between adjacent polyanions to form columns of anions and cations running along the b axis. This compound has also been investigated by IR, thermal, and solid-state, 13C and 31P MAS NMR spectroscopies and Ab initio calculations. 相似文献
90.
Experimental results presented in this work enable us to classify the three-dimensional structure of the detonation into
two fundamental types: a rectangular structure and a diagonal structure. The rectangular structure is well documented in the
literature and consists of orthogonal waves travelling independently from each another. The soot record in this case shows
the classical diamond detonation cell exhibiting ‘slapping waves’. The experiments indicate that the diagonal structure is
a structure with the triple point intersections moving along the diagonal line of the tube cross section. The axes of the
transverse waves are canted at 45 degrees to the wall, accounting for the lack of slapping waves. It is possible to reproduce
these diagonal structures by appropriately controlling the experimental ignition procedure. The characteristics of the diagonal
structure show some similarities with detonation structure in round tube. Pressure measurements recorded along the central
axis of the cellular structure show a series of pressure peaks, depending on the type of structure and the position inside
the detonation cell. Pressure profiles measured for the whole length of the two types of detonation cells show that the intensity
of the shock front is higher and the length of the detonation cell is shorter for the diagonal structures.
Received 17 May 2000 / Accepted 29 November 2000 相似文献