A quantum chemical study of silsesquioxanes: H8Si8O12, Me8Si8O12, H@Me8Si8O12, He@Me8Si8O 12 + , and He@Me8Si8O12

Quantum chemical PBE0 and B3LYP/cc-pVTZ, PBE0, B3LYP, RHF and MP2/6-31G(d,p) methods are employed to calculate the structural parameters of octa(silsesquioxane) H₈Si₈O₁₂ and octa(methylsilsesquioxane) Me₈Si₈O₁₂. These molecules and complexes H@Me₈Si₈O₁₂, He@Me₈Si₈O ₁₂ ⁺ , and He@Me₈Si₈O₁₂ have highly symmetric (O _h ) equilibrium configurations. With the use of the PBE0 method and a cc-pVTZ multicenter basis set common for the complex and its components coincidence is achieved between the calculated polarizability of a free He atom and the experimental value of 0.21 ų and the polarizability depression of 0.17 ų was found for He@Me₈Si₈O₁₂. In order to avoid the false conclusion about molecular symmetry the calculations of the structure of silsesquioxanes must be performed with sufficiently high accuracy (Int = ultrafine and Opt = tight in the use of the GAUSSIAN program).     

8',8"-去甲基三白脂素-8的全合成

以2-甲氧基酚,丁二酰氯和L-乳酸乙酯为起始原料,用会聚法完成了8',8"-去甲基三白脂素-8的全合成,总产率1.79%.其结构经1H NMR和MS表征.     

Total Synthesis of Several 8, 8",-Biflavones

8,8"-Biflavonoidsareantw0rtantclass0fbiflavonoids.Asasystematicresearchofthe8,8"-biflav0noids,wehavepreviouslyreportedthestudyonthereactionof2'-hydroxychaloneswithl2-H2SO4-DMSOsystem.'InthispaPer,thesynthesisof5,5",7,7',-tetTameth0xy-8,8"-biflavonela2,4,4",7,7"-tetramethoxy-8,8"-biflavone1b',4',4",,5,5,',7,7"-hexamethoxy-8,8"-biflav0ne1c4and4,4"-dibenZyl0xy-5,5",7,7"-tetramothoxy-8,8"-biflavoneldisreported.ThesyntheticmethodisshownintheSchemebelow.2-Hydroxyacet0phenonescondensedwithsubsti…     

Absorption spectra of 7, 7, 8, 8-tetracyanoquinodimethane in micellar solutions.

The absorption spectra of 7, 7, 8, 8-tetracyanoquinodimethane (TCNQ) with nonionic surfactant. Triton X-100, anionic surfactant, SLS and cationic surfactant, CTAB in aqueous and nonaqueous media have been studied. The spectral studies show that TCNQ forms 1:1 charge-transfer (CT) complex with Triton X-100 in both media. The aqueous solution of TCNQ shows an absorption maxima at 610 nm, which is unperturbed in the presence of SLS but is shifted to 650 nm in the presence of CTAB, indicating the interaction of TCNQ with the cationic surfactant and not with the anionic surfactant. In addition to this, the stability of TCNQ-Triton X-100 complex has been determined and the probable site of CT interaction has been pointed out.     

Investigation of solution‐grown,chain‐folded lamellar crystals of the even‐even nylons: 6 6, 8 6, 8 8, 10 6, 10 8, 10 10, 12 6, 12 8, 12 10, and 12 12

Chain‐folded lamellar crystals of the ten even‐even nylons: 6 6, 8 6, 8 8, 10 6, 10 8, 10 10, 12 6, 12 8, 12 10, and 12 12 have been grown from solution and their morphologies and structures studied using transmission electron microscopy, both imaging and diffraction. Sedimented mats were examined using X‐ray diffraction. The solution‐grown crystals are lath‐shaped lamellae and diffraction from these crystals, at room temperature, reveals that three crystalline forms are present in differing ratios. The crystals are composed of chain‐folded, hydrogen‐bonded sheets, the linear hydrogen bonds within which generate a progressive shear of the chains (p‐sheets). The sheets are found to stack in two different ways. Some p‐sheets stack with a progressive shear, to form the “α_p structure”; others sheets stack with an alternate stagger, to form the “β_p structure”. Both the α_p and β_p structures give two strong diffraction signals at spacings of 0.44 nm and 0.37 nm; these signals represent a projected intrasheet interchain distance (actual value 0.48 nm) and the intersheet spacing, respectively. Preparations of nylons 6 6, 8 6, 8 8, 12 6, and 12 8 consisted almost entirely of α_p‐structure material, with only a trace of β_p‐structure material being present. In contrast, nylons 10 6, 10 8, 10 10, 12 10, and 12 12 contained substantial quantities of both α_p‐ and β_p‐structure material, with α_p‐structure material always being in the majority. Preparations of nylons 10 8, 12 10, and 12 12 also showed an additional diffraction signal at 0.42 nm; this signal is characteristic of the pseudohexagonal (high temperature) structure. The melting temperature of solution‐grown lamellae of these even‐even nylons decreases with decreasing linear amide density. On heating, the strong diffraction signals (0.44 nm and 0.37 nm) gradually moved together and merge at the Brill temperature to form a single diffraction signal (0.42 nm), characteristic of the pseudohexagonal structure. This single diffraction signal remained until melting. For nylons 6 6, 8 6, 8 8, 10 6, and 12 6, the Brill temperatures were substantially below the respective melting temperatures and the single 0.42 nm diffraction signal was stable over temperature ranges of 14 °C to 56 °C, depending on the nylon. Conversely, nylons 10 8, 10 10, 12 8, 12 10, and 12 12 had coincident melting and extrapolated Brill temperatures. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1209–1221, 2000     

Editorial board page for “Synthetic Communications”, Volume 8, Number 8

This is a scanned image of the original Editorial Board page(s) for this issue.     

Editorial board page for “Analytical Letters”, Volume 8, Number 8

Abstract

This is a scanned image of the original Editorial Board page(s) for this issue.