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281.
Slobodan Gorjan Barbka Klemenc Marija Starič Branko Stanovnik Prof. Dr. Miha Tiŝler 《Monatshefte für Chemie / Chemical Monthly》1976,107(5):1199-1208
Diazotized 3-amino-1,2,4-triazole reacted with 1,3-cyclohexanedione or its 5,5-dimethyl derivative to give the tricyclic 1,2,4-triazine derivatives1 a and1 b. With 1,3-indanedione the tetracyclic compound8 was obtained. Compound1 a or the diacetyl derivative4 a are transformed in an acid catalyzed reaction into the fully aromatic system6 a with simultaneous rearrangement. Chemical reductions of systems1, 10 and12 have been investigated and the compounds9, 11 and13 were isolated and identified. Diazotized 2-aminothiazole readily formed the coupling products with reactive methylene compounds, but only14 could be prepared pure by cyclodehydration. 相似文献
282.
283.
Branko Kaitner Srećko I. Kirin Ernest Meštrović 《Journal of chemical crystallography》1995,25(3):117-122
The X-ray crystal structure of (R,S)--amino--caprolactone hydrochloride (compound1) and -amino--methyl--valerolactone hydrochloride semihydrate (compound2) are presented. Both compound1 and compound2 belong to the orthorhombic system. Caprolactone-hydrochloride1 crystallizes in the space groupP212121 witha=5.1948(7),b=8.7404(8),c=17.907(1) Å.V=813.0(2) Å3,Z=4. Valerolactone-hydrochloride2 crystallizes in the space groupP na21 witha=26.771(8),b=5.1598(7),c=13.201(3) Å,V=1823.5(7) Å3,Z=8. The lactone cations maintain the same, open envelope conformation in both crystals. The lactone-hydrochloride packing arrangements in1 and2 are distinctly different. While in1 N–H...Cl and N–H...O hydrogen bonding creates two dimensional nets in the form of puckered layers perpendicular to the [001] direction, in2 a water molecule of crystallization with an additional OW–H...Cl hydrogen interaction assists in forming a three-dimensional hydrogen-bond network throughout the crystal. 相似文献
284.
Transition structures for the 1,3-polar addition of azide anion to hydrogen cyanide, formaldimine, nitrogen, cis- andtrans -diazene, ethylene and acetylene were obtained at the MP2/6-31+G* theoretical model. The additions can be divided into two groups: addition to a triple bond, giving rise to an aromatic heterocyclic product, and addition to a double bond, forming a non-aromatic product. All transition structures correspond to a concerted mechanism for the polar cycloaddition. Symmetrical dienophiles, apart from cis-diazene, give rise to synchronous transition structures. The anomaly is explained in terms of strong n-n repulsion of the reactants in the transition structure. The reactivity of the compounds can be rationalized in terms of the bond orders of the newly forming bonds, from the frontier orbital energy differences and from the charge transfer from the azide anion to the dienophile. The quantitative correlation of the reactivity has been judged on the basis of the activation energies of the reactions calculated at MP2/6-31+G* and MP3/6-31+G*. It is predicted that the addition of azide to nitrogen is the slowest and that the additions to hydrogen cyanide and acetylene have the lowest barriers, in agreement with literature data. 相似文献
285.
AM1 computational study of cycloaddition reaction of vinyl sulfene generated from thiete 1,1-dioxide
Branko S. Jursic 《Journal of heterocyclic chemistry》1997,34(1):77-80
Theoretical studies of the cycloaddition reaction between vinyl sulfene, norbornene and related systems are presented. Since the parameterized AMI semiempirical method was used, the generated data are only of qualitative value. The vinyl sulfene reactivity was assessed by using frontier molecular orbital (FMO) energy gaps, bond orders, and the charge distribution of the reactants. To obtain more information, as far as the reaction outcome and its feasibility, the transition state structures and activation barriers for competitive pathways are computed. 相似文献
286.
Gligor Jovanovski Branko Kaitner Orhideja Grupce Pance Naumov 《Central European Journal of Chemistry》2004,2(1):254-275
The crystal structure of tripotassium trisaccharinate dihydrate, K3(C7H4NO3S)3·2H2O, is triclic, space group\(P \bar 1, Z = 2\). It consists of three crystallographically independent potassium and saccharinato ions as well as two structurally different water molecules. Potassium coordination polyhedra are irregular, with K1 and K3 six-coordinated and the third one K2 seven-coordinated. The K?O distances range from 2.652(9) to 3.100(2) Å(mean: 2.790 Å) whereas the K?N distance is 3.025(3) Å. The water molecules W2 is disordered over three positions with occupancies of approximately 0.6, 0.2 and 0.2. The hydrogen atom (H1W1) of the ordered water molecule (O1W) is hydrogen bonded to the sulfonyl oxygen atom (O11) (R(O...O)=2.976(3) Å), whereas the other hydrogen atom (H2W1) is bifurcated to the carbonyl oxygen atom (O13) (R(O...O)=2.851(3) Å) and the disordered water molecules (O23W) (R(O...O)=3.067(12) Å). The carbonyl oxygens (O13, O23 and O33) and one of the disordered water molecules (O22W) are involved in C?H...O hydrogen bonds (R(C?H...O)=3.027(4)–3.304(9) Å). Structural characteristics of the studied compound are compared with the analogous trisodium trisaccharinate dihydrate and dipotassium sodium trisaccharinate monohydrate. Infrared and Raman spectra of the title compound have been analyzed in relation to the structure, and compared with the spectra of trisodium trisaccharinate dihydrate. 相似文献
287.
The AM1 semiempirical method was used for theoretical searching of activation of thiophene as a diene for the Diels-Alder reaction. The reactivity of thiophene, electron-withdrawing and electron-donating substituted thiophenes, as well as the S-methylthiophenium ion were studied as the diene for Diels-Alder reactions by evaluating their frontier orbital energies and by calculating reaction barriers with activated and deactivated dienophiles. It was demonstrated that slight activation of the thiophene ring can be obtained with both electron-donating and electron-withdrawing groups attached to the thiophene ring. It was predicted that the actual transformation of thiophenes into the corresponding S-methylthiophenium anions is the best means of activating the thiophenes. The calculated activation energies for normal (non-activated) dienophiles are moderate so mild reaction conditions are predicted. If dienophiles are activated with electron-donating substituents, AM1 calculations predict a two step cycloaddition reaction with a very small activation barrier. 相似文献
288.
Sonja Strah Amalija Golobi
Ljubo Goli
Branko Stanovnik 《Journal of heterocyclic chemistry》1997,34(5):1511-1517
Alkyl (E,Z)-2-(2-benzoyl-2-ethoxycarbonyl-1-ethenyl)amino-3-dimethylaminopropenoates 1a,b react with het-eroarylamines 2 to give alkyl 2-(2-benzoyl-2-ethoxycarbonyl-1-ethenyl)amino-3-heteroarylaminopropenoates 3-13 . These were cyclized into fused 3-(2-benzoyl-2-ethoxycarbonyl-1-ethenyl)amino-4H-azolo- (or azino)-pyrim-idin-4-ones 14-18 . 2-Benzoyl-2-ethoxycarbonyl-1-ethenyl group can be easily removed from 3-(2-benzoyl-2-ethoxycarbonyl-1-emenyl)amino-8-memyl-4H-pyrido[1,2-a]pyrimidin-4-one ( 14 ) to give 3-amino-8-methyl-4H-pyrido[1,2-a]pyrimidin-4-one ( 19 ). The structure of 1a was confirmed by X-ray analysis. 相似文献
289.
The synthesis of new tetracyclic systems and new stable tautomers of known systems 11H- 13 and 10H-imidazo[1, 2-b]pyrazolo[4, 3-d]-s-triazolo[3, 4-f]pyridazine 16 , 9H-pyrazolo[3, 4-d]bis-s-triazolo[4, 3-6:5′,1-f]-pyridazine 15 , 10H-pyrazolo[3, 4-d]bis-s-triazolo[4, 3-b:3′,4′-f]pyridazine 17 , and 10H-pyrazolo[4, 3-d)bis-s-triazolo[4, 3-6:5′,1′-f]pvridazine 18 is described. 相似文献
290.
Haishan Zeng Calum MacAulay David I. McLean Branko Palcic Harvey Lui 《Photochemistry and photobiology》1998,68(2):227-236
To study the temporal dynamics of human skin autofluorescence photobleaching, we measured the autofluorescence spectral changes of skin in vivo during continuous exposure to 442 nm (He-Cd) laser light. Integral intensities were calculated for various spectral wavelength bands and plotted as a function of time. Mathematical analysis of the time function revealed a double-exponential photobleaching process: I(t) = a exp(-t/τ1,) + b exp(-t/τ2) + c, in which t1, and t2 differed by an order of magnitude. A hypothesis for the mechanism of the double-exponential photobleaching dynamics was proposed and evaluated using Monte Carlo modeling of light propagation in the skin and autofluorescence escape from skin. By combining the fluorophore microdistributions, Monte Carlo simulation results and the variation in fluorescence decrease parameters (a, b, c, τ1τ2) with increasing exposure intensities a biophysical explanation for the double-exponential photobleaching function was elucidated. The fast decrease term corresponds to laser-induced photobleaching in the stratum corneum, while the slow decrease term represents fluorophore changes in the dermis. The measured autofluorescence photobleaching dynamics can be used to determine the fractional contributions of different skin layers to the total autofluorescence signal measured in vivo. 相似文献