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31.
Extremal hexagonal chains 总被引:6,自引:0,他引:6
Ivan Gutman 《Journal of mathematical chemistry》1993,12(1):197-210
Some extremal properties of the linear chainL
h ofh hexagons are pointed out. In the class of all hexagonal chains withh hexagons,L
h has minimumK,Z andx
1 values, as well as maximum W and values;K = number of perfect matchings,Z = number of independent edge sets (Hosoya index),x
1 = largest graph eigenvalue,W = Wiener index, = number of independent vertex sets (Merrifield-Simmons index). The extremality ofL
h with respect toZ, andx
1 is demonstrated here for the first time.Dedicated to Frank Harary, teacher, inspirer and friend, pioneer, champion and proprietor of graph theory, on the occasion of his 70th birthday. 相似文献
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P. V. Snytnikov K. V. Yusenko S. V. Korenev Yu. V. Shubin V. A. Sobyanin 《Kinetics and Catalysis》2007,48(2):276-281
The performance of a Co-Pt powder and of Co-Pt catalysts supported on γ-Al2O3 and on the graphite-like carbon material Sibunit in selective CO oxidation in hydrogen-containing mixtures is considered. Fine particles of metal-metal solid solutions and intermetallides were obtained by the decomposition of a Co- and Pt-containing double complex salt in a hydrogen atmosphere at ~400°C. As compared to their Pt and Co monometallic counterparts, the bimetallic catalysts are more active and allow the CO concentration in hydrogen-containing mixtures to be reduced from 1 to 10?3 vol %. This effect is likely due to the formation of bimetallic particles of a Co-Pt solid solution on the support surface. 相似文献
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A. M. Genaev G. E. Sal’nikov V. G. Shubin 《Russian Journal of Organic Chemistry》2007,43(8):1134-1138
By DFT method energy barriers were calculated for carousel rearrangements of bicyclo[3.1.0]hexenyl, cyclobutenyl, and homotropylium cations. A plausible agreement between calculated and experimental findings was found. 相似文献
38.
Jacobson MA Keresztes I Williard PG 《Journal of the American Chemical Society》2005,127(13):4965-4975
N-Lithio-N-(trialkylsilyl)allylamines can be deprotonated in the presence of ethereal solvents exclusively at the cis-vinylic position to yield 3,N-dilithio-N-(trialkylsilyl)allylamines under mild conditions. Low temperature (1)H and (7)Li NMR ((1)H NOESY, TOCSY, (1)H/(7)Li HSQC, and DO-NMR) studies on the solution structure of 3,N-dilithio-N-(tert-butyldimethylsilyl)allylamine identified three major aggregates in THF (monomer, dimer and tetramer), but the aggregate structures failed to explain the solvent dependence and regiochemical outcome of the reaction. Low temperature (1)H NMR (NOESY, TOCSY, DO-NMR) studies on the solution structure of N-lithio-N-(tert-butyldimethylsilyl)allylamine in the presence of nBuLi identified amide/nBuLi mixed aggregates in both the ethereal solvent THF (1:1 dimer) and the hydrocarbon solvent toluene (1:3 tetramer). Addition of 2 equiv of THF to toluene solutions induces the formation of the same THF solvated 1:1 dimer as observed in neat THF. NMR evidence suggests that in THF the mixed aggregate has close contact between the olefin and the beta-CH(2) of nBuLi, while in the absence of THF, the allyl chain appears to be pointed away from the nearest nBuLi residues. 相似文献
39.
Wolfgang A. Herrmann Carl Krüger Richard Goddard Ivan Bernal 《Journal of organometallic chemistry》1977,140(1):73-89
μ-Carbonylbis(carbonyl-ν5-cycopentadienylrhodium)(Rh—Rh) reacts with N-methyl-and N-ethyl-N-nitrosourea in boiling benzene to yield the dinuclear, diamagnetic, neutral rhodium complexes μ-methylene- (A) and μ-ethylidenebis(carbonyl-η5-cyclopentadienylrhodium)(Rh—Rh) (B), respectively. Deuterium labelled experiments prove the origin of the metal-stabilized methylene ligand to be the alkyl group of the organic precursor. This new method of preparation of transition metal—methylene complexes may be used as an alternative to the commonly used diazo method; the latter method was shown to work with diazodiethylmalonate and dicarbonyl-η5-cyclopentadienylrhodium, the reaction yielding μ-bis(ethoxycarbonyl)methylenebis(carbonyl-η5-cyclopentadienylrhodium)(Rh—Rh).Compound A crystallizes in the triclinic system, P, and with cell constants of a 803.42(5), b 909.98(6), c 938.81(2) pm, α 74.402(3), β81.923(3), and γ 83.685(6)°. The unit cell volume and the calculated density are 651.6 Å3 and 2.069 g cm-3, for one molecule in the asymmetric unit. The molecular geometry of μ-CH2[η5-C5H5Rh(CO)]2 was established from 2718 unique reflections collected with a computer-controlled diffractometer and refined to a final R(F) = 0.0379. The molecular parameters derived from the single-crystal X-ray study conform to a remarkable degree with those found for μ-CO[η5-C5H5Rh(CO)]2. Thus, the bridging ligands CH2 and CO seem to be analogous in their effects on the structural characteristics of the molecular framework of the two molecules. 相似文献
40.
Ivan Ernest 《Helvetica chimica acta》1979,62(8):2681-2694
A synthesis of (6 R, 7 R)-7-acylamino-2-oxocephem-4-carboxylic acids from penicillins is reported based on the formation of the 2-oxocephem system in an intramolecular Wittig condensation. An interesting steric effect of the acylamino grouping on the course of this key step was used to advantage. Some physical and biological properties of this new type of Δ3-cephem are described. 相似文献