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1.
2.
The strain energies and through-space distances between the two bridgehead E atoms of a selection of 1,3-dimethyl-1,3-ditetrelbicyclo[1.1.1]pentanes
(tetrel E = Si, Ge or Sn) were examined by quantum chemical calculations at MP2 and B3LYP levels. The aim is to identify which
bridges lead to short through-space E,E distances, and simultaneously, to as low strain as possible. A short E,E distance
should improve through-space interaction, and a low strain should promote the thermal stability and possibly also facilitate
their synthesis. The bridges examined included CH2, CMe2, CtBu2, C(CH2)n (n = 2–4), O, NMe, S, PMe, SiMe2, GeMe2, and SnMe2. The calculations indicate that the phospha bridge is a good compromise providing reasonably low strain as well as E,E through-space
distances which are only longer than normal E–E single bonds by factors of 1.06–1.10.
This paper is dedicated to Professor Mitsuo Kira in recognition of his stimulating Si chemistry and his 2005 Wacker Award. 相似文献
3.
Veronica?StigssonEmail author G?ran?Kloow Ulf?Germg?rd Niclas?Andersson 《Cellulose (London, England)》2005,12(4):395-401
Controlling the reduction in molecular weight of the cellulose chains is essential in the production of carboxymethyl cellulose
(CMC). Such a reduction can be achieved by the addition of cobalt during the process of cobalt(II) ions, which act as a catalyst
for oxidative cleavage, and the influence thereof has been studied under a variety of conditions. This study has resulted
in a model that summarises the effects of the added amount of cobalt, the time for the cobalt reaction, the temperature in
the mercerisation stage of the CMC-manufacturing process and finally the effect of the temperature in the etherification stage.
It is shown that it is important for cobalt to be present during the mercerisation stage in order to achieve the desired viscosity. 相似文献
4.
5.
S. P. Singh S. S. Parmar V. I. Stenberg S. A. Farnum 《Journal of heterocyclic chemistry》1978,15(1):13-16
The 13C nmr chemical shifts of phenylbutazone, oxyphenbutazone, indomethacin and indole-3-acetic acid are reported. The assignments of various carbon resonances are made on the basis of the substitution effects on benzene shifts, multiplicities generated in SFORD spectra, nuclear overhauser enhancement for protonated carbons, and the comparison with analogous compounds. 相似文献
6.
Virgil I. Stenberg Nand K. Narain S. P. Singh Ralph H. Obenauf M. J. Albright 《Journal of heterocyclic chemistry》1977,14(3):407-410
The 15N and 13C nmr spectra of physostigmine are discussed along with complete assignment of the signals. This alkaloid 15 N nmr spectrum is notable because it contains nitrogens in three different environments. 相似文献
7.
N. C. van de Merbel M. Stenberg R. Öste G. Marko-Varga L. Gorton H. Lingeman U. A. Th. Brinkman 《Chromatographia》1995,41(1-2):6-14
Summary A two-dimensional, column liquid chromatographic system is used for the determination of the D- and L-enantiomers of amino acids in biological samples. Separation of the amino acids is first on ion-exchange column by gradient elution with a sodium citratesodium chloride buffer. Enantioseparation is by subsequent injection of 3 l heart-cuts of the individual amino acids onto a second column with a chiral crown ether stationary phase. Finally, fluorescence detection is after post-column labelling of the amino acids using ano-phthalaldehyde-2-mercaptoethanol reagent solution. The high separation power and selectivity of the system allow processing of complex samples with hardly any additional treatment and the determination of small quantities of D-amino acids in the presence of excess L-form. Applicability of the system is illustrated by the determination of D- and L-aspartate, serine, glutamate and alanine in various complex biological samples, such as protein hydrolysates, urine and biotechnological and food samples. Data are given on detectability, repeatability and linearity. 相似文献
8.
J. A. Van Allan G. A. Reynolds J. F. Stenberg 《Journal of heterocyclic chemistry》1979,16(8):1661-1662
A general method for the preparations of pyranthiones is particularly useful for preparing substituted xanthiones which are unavailable by established procedures. Reaction of a xanthone with p-tosyl isocyanate or with trichloroacetyl isocyanate produces the corresponding imino derivatives, which upon treatment with n-butylamine followed by hydrogen sulfide gives the desired xanthione in good yield. 相似文献
9.
[n.n.n]Propellanes and bicyclo[n.n.n]alkanes (1=n=3) in which the bridgeheads and bridges are composed of different Group 14 elements will not be ideal homologues of the all-carbon propellanes and bicycloalkanes. We used quantum-chemical calculations to conclude which of these could possibly be stable at ambient temperature. Structures, strain, and dimerization energies of [n.n.n]propellanes and bicyclo[n.n.n]alkanes with C-based tethers and with Si, Ge, or Sn at the bridgehead positions were calculated. The aptitude to add water was probed in selected cases. Comparisons were made with the analogous all-C propellanes and bicycloalkanes. All heavy 1,(n+2)-dimetallabicyclo[n.n.n]alkanes should be thermally stable and suitable synthetic targets, even though the moisture sensitivity of 1,3-dimetallabicyclo[1.1.1]pentanes increases as Group 14 is descended. For 1,(n+2)-dimetalla[n.n.n]propellanes, the incompatibility between the tether and M--M bond lengths impacts strongly on structure and stability. At ambient temperature 1,3-disila[1.1.1]propellanes should oligomerize instantly upon formation, whereas 1,3-digerma- and 1,3-distanna[1.1.1]propellanes should be less prone to oligomerize and possibly isolable. The 1,4-dimetalla[2.2.2]propellanes with M=Si-Sn have biradical ground states and can presumably only be observed under inert conditions at cryogenic temperatures. Finally, we predict that 1,5-disila[3.3.3]propellane will be persistent at ambient temperature, but 1,5-distanna[3.3.3]propellane should rapidly oligomerize. 相似文献
10.
Paresh J. Kothari Shiva P. Singh Surendra S. Parmar Virgil I. Stenberg 《Journal of heterocyclic chemistry》1980,17(7):1393-1398
Several 1-(5-aryl-2H-tetrazol-2-ylacetyl)-4-substituted thiosemicarbazides and 5-(5-aryl-2H-tetrazol-2-yl-methyl)-4-substituted-s-triazole-3-thiols were synthesized as possible antiinflammatory agents. These compounds were characterized by their elemental, infrared and nuclear magnetic resonance analysis. 相似文献