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31.
32.
A synthetic procedure for the preparation of the unusual charge-separated pyridinium barbiturate zwitterion 2 from 1,3-dimethylbarbituric acid and 2-pyridinecarbaldehyde in methanol was developed. The structure of the compound was confirmed with X-ray analysis to demonstrate the strong charge separation throughout the molecule. One would expect that this charge separation would increase its reactivity; however, contrary to this expectation, the compound is very stable in acidic media, and in the presence of a base, decarbonylation occurs on one barbituric acid while the zwitterionic moiety of the molecule stays intact. 相似文献
33.
All-E or E,Z,E-oligoprenols may be synthesized from allylic stannanes by reaction with prenyl aldehydes. [reaction: see text] 相似文献
34.
35.
Branko Grünbaum 《Discrete Mathematics》1973,5(3):241-246
A1 least three planes are needed in order to cut all edges of a 3-dimensional centrally symmetric convex polytope by planes which miss all vertices of the polytope. In contrast, there exist centrally symmetric convex tessellations of the 2-sphere for which two planes are sufficient. 相似文献
36.
Slobodan Gorjan Barbka Klemenc Marija Stari? Branko Stanovnik Miha Ti?ler 《Monatshefte für Chemie / Chemical Monthly》1976,7(1):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
37.
Angelovski G Costisella B Kolarić B Engelhard M Eilbracht P 《The Journal of organic chemistry》2004,69(16):5290-5294
Azamacrocyclic fluorophores containing piperazine units were synthesized using sequential rhodium-catalyzed regioselective hydroformylation-reductive amination. A piperazine unit is introduced into the macrocycles to act simultaneously as electron donor and binding site. The macrocycles chelate divalent cations, either Zn2+ or Co2+, which considerably enhanced fluorescence. Complexation with Zn2+ was additionally confirmed by NMR. 相似文献
38.
Damjana Miheli
Renata Jake Jurij Svete Branko Stanovnik Simona Goli Grdadolnik 《Journal of heterocyclic chemistry》2001,38(6):1307-1312
(S)‐5‐Benzoyloxymethyl‐3‐[(E)‐(dimethylamino)methylidene]tetrahydrofuran‐2‐one (6), prepared in 5 steps from L‐glutamic acid (1), was used as precursor in a one step ‘ring switching’ synthesis of (S)‐2‐hydroxy‐3‐heteroaryl‐l‐propyl benzoates 13‐18, 23, 24. In the reaction of 6 with 2‐aminopyridine (21) and 2‐amino‐4,6‐dimethylpyrimidine (22) the corresponding dimethylamine substitution products (25, 26) were obtained. 相似文献
39.
N. Grunbaum L. Dessemond J. Fouletier F. Prado L. Mogni A. Caneiro 《Solid State Ionics》2009,180(28-31):1448-1452
The electrode reaction of porous La0.6Sr0.4Co0.8Fe0.2O3?δ films deposited onto Ce0.9Gd0.1O1.95 (CGO) was investigated by impedance spectroscopy within the temperature and oxygen partial pressure (pO2) ranges of 500 ≤ T ≤ 700 °C and 10? 4 < pO2 < 1 atm, respectively, using Ar and He as gas carriers. The electrochemical impedance spectroscopy (EIS) measurements reveal a high frequency (HF) and a low frequency (LF) regions in the Nyquist plane. The high frequency (HF) region was fitted with a Warburg-type impedance element, and the low frequency (LF) region was reproduced with a resistance in parallel to a constant phase element. Both, the slight dependence of the polarization resistance (RW) and the small variation of the apex frequency (fv) of the HF Warburg-type element, on pO2, suggest that this contribution corresponds to the oxygen diffusion in the bulk of the La0.6Sr0.4Co0.8Fe0.2O3?δ electrode material. The variation of the polarization resistance of the LF region (Rrcpe) with pO2 indicates that as T increases, the limiting step evolves from dissociative oxygen adsorption to oxygen gas diffusion in the pores of the mixed ionic/electronic conductor (MIEC) electrode. 相似文献
40.