摘要:

AbstractThe electronic structures of six cubane‐like cluster compounds of the type [Fe4S4L4]n(L = SH, OH, and Cl,n=‐2 and −3; L=NO,n= 0 and −1) have been calculated by using DV‐Xαmethod, and the bonding properties are discussed with emphasis on the ligand effect on cluster bonding. The comparisons of MO energies and cluster charge distributions with the experimental data are made, and the differences between the early studies and the present one are also briefly

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080102

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractHydrogen bonding interaction in hydrogen fluoride dimer has been investigated by quantum‐chemical calculation with 6‐311G**basis set at various mutual orientations. Atomic charges and charge transfer have been calculated by means of potential‐derived method, and decomposition of hydrogen bonding interaction has been executed. The calculation results show that there is a variation range for the energy‐stable orientations, the charge transfer in the range presents maximum value, and the charge transfer interaction plays a decisive role in the hydrogen

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080103

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe ion transfer of the basic dye rhodamine B at the interface between water and nitrobenzene, water and 1, 2‐dichloroethane, as well as water and nitrobenzene ‐ chlorobenzene mixtures has been studied by cyclic voltammetry and chronopotentiometry with linear current scanning. A transfer mechanism of rhodamine B is proposed in terms of its electrochemical behavior, dissociation and distribution equilibria, and is ascribed as diffusion‐controlled reversible process of rhodamine B. The experimental data obtained for the relationship between interracial half‐wave potential ΔWoφ° and pH are in agreement with the theoretical equation based on the mechanism, and the standard interfacial potential differences ΔWoφ° and standard Gibbs energies ΔWoG° are calculated by extrapolation. The effect of the nature of solvent on the transfer behavior and the stability of the interface have

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080104

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractA mixed ligand neodymium complex containing 1‐phenyl‐3‐methyl‐4‐trifluoroacetyl‐pyrazol‐5‐one (HPMTFP) and 1‐phenyl‐3‐methyl‐pyrazol‐5‐one (PMP), with molecular formula Nd (PMTFP)3·PMP·H2O was synthesized. Its crystal and molecular structure has been determined by single crystal X‐ray diffraction method. The complex crystallizes in monoclinic system with space groupC52‐P21/n. There are four formula units in a cell of dimensionsa= 12.837(3),b= 23.763(5),c= 16.810(4) Å, β = 109.58(2)°. The structure has been refined by full‐matrix least‐squares techniques to a finalRvalue of 0.0487 andRwvalue of 0.432. The neodymium atom is coordinated to eight oxygen atoms with the average Nd—O bond length 2.439Å. Its thermostabi

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080105

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe crystal structure of a new type arylarsonic polytungstate [C(NH2)3]4[p‐NH3C6H4As)2W6O25]·4H2O was determined by single‐crystal X‐ray diffraction analysis. It belongs to triclinic, space group\documentclass{article}\pagestyle{empty}\begin{document} \[ P\bar 1 \] \end{document}, with cell dimensionsa= 12.863(3),b= 18.912(3),c= 21.383(4) Å α = 91.14(2)°, β = 93.65(3)°, γ = 92.25(3)°,V= 5185.9 Å3,Z= 4,Dc= 2.753 g/cm3. The intensity data were collected on an Enraf‐Nonius CAD4 diffractometer with MoKαradiation. The positions of all tungsten and arsenic atoms were determined by direct method. The other non‐hydrogen atoms were revealed by difference Fourier synthesis. The structure was refined by fullmatrix least‐squares procedure to a finalRvalue of 0.070. The crystal structure contains two similar but nonidentical molecules. Two similar anions consist of a ring of six WO6octahedra, which are connected with one face‐sharing, two corner‐sharings and three edge‐sharings, and twop‐aminophenylarsonic tetrahedra capped above and below the ring. In each WO6ring, four tungsten atoms, which are joined with edge‐sharing oxygen atoms, are almost coplanar, while the two others, which are joined with face‐sharing oxygen atoms, protrude out of the ring towards the same side. The two arsenic atoms in each anion are not equivalent in their bonding manner. In each anion, all non‐hydrogen atoms of each organic group are in the same plane. Each molecule contains one anion, four C(NH2)3+ cations and four water molecules. There are many hydrogen bonds between cations and anions throughout the whole crystal. The amino groups can accept protons, so that the charge of the resulting anion decreases and [(RAs

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080106

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractWang's phase filtering procedure has been applied to the structure study of trichosanthin crystals belonging to space group C2. The MIR phases at 3Å resolution have been improved with the accumulative phase shift of 31.8° and the figure of merit has been improved from 0.54 to 0.84. The resulted electron density map at 3Å resolution has been much improved with a higher ratio of the electron density of the protein to the noise in the solvent region. The minimap has been interpreted more reasonably than the previous maps, giving the overall course of the polypeptide chain substantially the same as previously reported except for containing more secondary structure and a few short segments traced differently. The first 85 Cαatoms of the polypeptide chain are located in about the same positions as determined previously with an exception of a short segment but the amino acid residues after that shift along the chain with a maximum shift of about 15 residues. The electron density of side chains agrees better with the primary structure. The conformation and the three‐dimensional structure as well as the major heavy‐atom binding sites for the two molecules in an asymmetric unit are substantially the same. The structure of trichosanthin shows more similarity to ricin A chain than that reported pre

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080107

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractHypocrellin A and B in methanol were autosensitized and photooxygenated to 1, 4, 6, 7 and 2, 5, 8, 9 respectively. 1 in methanol was photooxygenated to 6 and 7 under the sensitization by HB. 1 in methanol was photooxygenated to 7 under the sensitization by Rose bengal. 1 in benzene irradiated with medium‐pressure‐mercury lamp was photolyzed to 3 in the presence of iod

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080108

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe singlet‐singlet intramolecular energy transfer between naphthalene moiety and dansy! group held apart by a rigid steroid bridge was investigated for two molecules: β‐(1‐naphthyl) acetoxy‐17α‐dansyl‐Δ5androstene (3a) and 3β‐(1‐naphthyl)acetoxy‐17 β‐dansyl‐Δ5androstene (3b). The rates of energy transfer for 3a and 3b in cyclohexane are 6.9 × 106and 1.1 × 108s−1respectively. The difference in energy transfer rate between 3a and 3b is attributed to the different donor‐acceptor separation and orientation. The ratio of the two epimers in the synthesized product mixture was obtained from th

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080109

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractN,N‐deithyl‐iododifluoroacetamide 1 reacted with alkenes, alkynes in aqueous acetonitrile solutions of sodium dithionite and sodium hydrogen carbonate at room temperature to give the corresponding adducts, thus constituting a new method for introducing the CF2group into organic molecules. Compound 1 reacted with conjugated olefins 2b, c to afford the iodine‐free adducts 7b, c. The adducts 3d—f, from addition of 1 to alkenes 2d—f, could be converted into α,α‐difluoro‐γ‐lactones 5d—f by treatment with silica gel. Compound 1 reacted with ethyl vinyl ether 2i to give aldehyde 8, and perfluoroalkyl or polyfluoroalkyl iodides reacted similarly. A radical mechanism was proposed for the addition reaction. Under the same condition,N,N‐diethyl‐bromodifluoroacetamide produced only the corresponding su

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080110

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThis paper describes the total synthesis ofcis‐shisool through intermediate 3, which was derived from the Diels‐Alder adduct 4 (or 5). The structure of the isomers produced by the Diels‐Alder reaction of cyclohexadiene and crotonate has been elucidated by means of GC and NMR. Methylenation of 12 with Zn‐CH2Br2‐TiCl4or Ph3P=CH2retains the stereochemistry of the carbon atom adjacent to the carbo

ISSN:1001-604X    

DOI:10.1002/cjoc.19900080111

出版商:WILEY‐VCH Verlag    

年代:1990

数据来源: WILEY