排序方式: 共有52条查询结果,搜索用时 203 毫秒
41.
Michael Ramek Sanja Tomi Biserka Koji-Prodi 《International journal of quantum chemistry》1996,60(8):1727-1733
An ab initio conformational analysis of 4-chloroindole-3-acetic acid was performed at the RHF/6-311G * * level. The mirror symmetrical conformer (in which the indole ring is coplanar with the COOH group) is most stable; next in energy are the two conformers with the C—COOH fragment perpendicular to the indole ring with relative energies of 2.72 and 6.69 kJ/mol. H(SINGLEBOND)Cl hydrogen bonding results in only a minor stabilization. The results are combined with those obtained earlier for indole-3-acetic acid and recent biological data regarding auxin (growth hormone) activity. From this, assumptions concerning the biologically active conformation are drawn. © 1996 John Wiley & Sons, Inc. 相似文献
42.
Berislav Peri Biserka Koji‐Prodi Janja Makarevi Milan Joki Mladen
ini 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(6):747-748
The title compound, 2,2′‐(oxalyldiimino)bis(3‐methylbutanoic acid), C12H20N2O6, possesses a centre of symmetry. In the crystal, molecules are connected by hydrogen bonds between oxamide and carboxyl groups, similar to the pattern of the monoclinic forms of HO–Gly–CO–CO–Gly–OH and HO–Aib–CO–CO–Aib–OH (Gly is glycine and Aib is 2‐aminoisobutyric acid). The characteristic torsion angles in the title compound are close to those in peptide α‐helices. 相似文献
43.
Jaroslav Horvat Branimir Klaić Biserka Metelko Vitomir Šunjić 《Tetrahedron letters》1985,26(17):2111-2114
Based on the intermediates revealed by 13C-NMR spectroscopy, the mechanism of levulinic acid () formation in acid catalysed hydrolysis of 2-hydroxymethylfurane () and 5-hydroxymethylfuran-2-carbaldehyde () is proposed. 相似文献
44.
Borislav Bogdanovi Biserka Henc Arnold Lsler Burkhard Meister Horst Pauling Günther Wilke 《Angewandte Chemie (International ed. in English)》1973,12(12):954-964
The progress made in the field of homogeneous catalysis during the last five to six years has led, inter alia, to the development of highly selective catalysts for asymmetric syntheses. Homogeneous asymmetric hydrogenation, using well defined transition metal catalysts, may be achieved with optical yields of 85 to 90% or more. Catalytic reactions, in which the chiral centers are generated by C? C bond formation, can result in optical yields of 70 to 80%. The hydrogenation catalysts consist primarily of rhodium(I) complexes containing “Homer phosphanes”, phosphanes with chiral C atoms, or optically active amides. Catalysts which induce optical activity through the formation of C? C bonds have been developed from π-allylnickel halides, Lewis acids, and phosphanes containing chiral C atoms. The results obtained signify a breakthrough in an area of catalysis previously restricted to syntheses involving enzymes. 相似文献
45.
Berislav Peri Janja Makarevi Milan Joki Biserka Koji‐Prodi Mladen
ini 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(7):865-867
In the title compound, C20H22N4O4·C2H6OS, two distinct hydrogen‐bond systems connect oxalamide groups in one pattern and primary amide groups in the other to form a two‐dimensional network perpendicular to the c axis. These hydrophilic layers are joined to the three‐dimensional structure through C—H?π interactions. The hydrogen‐bonded waved layers shape holes which are occupied by disordered dimethyl sulfoxide solvent molecules. 相似文献
46.
Milan Jokić Miroslav Bajić Mladen Žinić Berislav Perić Biserka Kojić-Prodić 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(11):1354-1355
The molecule of benzene-1,4-dicarboxamidine or benzdiamidine, C8H10N4, reveals Ci symmetry. Hydrogen bonds utilize the amino groups as double donors, whereas the imino groups act as double acceptors. The network formed is similar to that observed in the crystal packing of terephthalamide. 相似文献
47.
48.
Dijana Pešić Ivana Ozimec Landek Ana Čikoš Biserka Metelko Vesna Gabelica Barbara Stanić Mladen Merćep Milan Mesić 《Journal of heterocyclic chemistry》2007,44(5):1129-1133
Synthesis of a novel heterocyclic class of compounds, 1‐aza‐dibenzo[e,h]azulenes [1] ( 6a‐c and 7a‐c ), derived from dibenzo[b,f]oxepin, its 8‐chloro analogue and dibenzo[b,f]thiepin, respectively, is described. Aldol condensation of the starting ketones 4a‐c with (dimethyl‐hydrazono)‐acetaldehyde affords hydrazonoethylidene derivatives 5a‐c , which on reduction with sodium dithionite and subsequent cyclization provide the target tetracyclic 1‐aza‐dibenzo[e,h]azulenes 6a‐c . Regiospecific formylation of 6a‐c with Vilsmeier reagent leads to 2‐formyl derivatives 7a‐c . A series of derivatives 6a‐c and 7a‐c was tested for antiinflammatory activity as potential inhibitors of tumor necrosis factor alpha (TNF‐α) production in vitro. 相似文献
49.
Biliškov N Kojić-Prodić B Mali G Molčanov K Stare J 《The journal of physical chemistry. A》2011,115(14):3154-3166
Hydrogen bonding and proton transfer in the solid state are studied on the crystals of isostructural anhydrous potassium and rubidium complex chloranilates by variable-temperature single crystal X-ray diffraction, solid state (1)H NMR and IR spectroscopies, and periodic DFT calculations of equilibrium geometries, proton potentials, and NMR chemical shifts. Their crystal structures reveal neutral molecules of chloranilic acid and its dianions connected into a chain by O-H···O hydrogen bond. A strong hydrogen bond with a large-amplitude movement of the proton with NMR shift of 13-17 ppm and a broad continuum in IR spectra between 1000 and 500 cm(-1) were observed. Periodic DFT calculations suggest that proton transfer is energetically more favorable if it occurs within a single pair of chloranilate dianion and chloranilic acid molecule but not continuously along the chains of long periodicity. The calculated chemical shifts confirm the assumption that the weak resonance signals observed at lower magnetic fields pertain to the case when the proton migrates to the acceptor side of the hydrogen bond. The detected situation can be described by a partial proton transfer. 相似文献
50.
Krešimir Molčanov Tomislav Portada Vesna Čaplar Milan Jokić Janja Makarević Nataša Šijaković Vujičić Zoran Štefanić Mladen Žinić Biserka Kojić-Prodić 《Structural chemistry》2013,24(2):597-609
Preparation, structural characterisation and topology of hydrogen bonding networks of bis(phenylglycinol)malonamide, as well as its Cα mono- and dialkyl-substituted derivatives are described. Their hydrogen bonding motifs are described in view of their gelling properties. Topology of hydrogen bonding typical of malonamide gelators is compared with those of well-examined oxalamide gelators. 相似文献