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1.
The results from structure studies on 6a-thiathiophthenes show that different substituent groups perturb the bonding in the three-sulphur sequence to different degrees. Both equal and unequal S? S bonds occur in symmetrically as well as in unsymmetrically substituted derivatives. The specific effect of methyl and phenyl substituents on the sulphur-sulphur bonding may be described by the results from CNDO/2 calculations on mono-methyl and mono-phenyl substituted 6a-thiathiophthenes. Molecular packing and intermolecular close contacts also seem to affect the S? S bonding. The structures of equally substituted 6a-thiathiophthene analogues with and show, when compared with the equivalent 6a-thiathiophthene, that and cause a pronounced change in the S? S bonding, while the perturbation caused by is negligible. In symmetrical 6a-thiathiophthene analogues with and , the average bond length in the linear three-atom sequence is 9 – 12% longer than the respective single bond.  相似文献   

2.
In the density-functional theory of the ground state of an electronic system there arise the concepts of softness, hardness, local softness, and local hardness. Definitions of these quantities are reviewed, and then local softness and local hardness are discussed in some detail. The local softness of a species, the derivative , is a measure of the chemical reactivity of a site in the molecule. From it can be obtained the total global absolute softness in the sense of Pearson and a normalized chemical reactivity index of frontier type. Several formulas for s( r ) are obtained, including new fluctuation formulas, and its determinative role in chemisorption, catalysis, and frontier-controlled charge-transfer processes is briefly discussed. Local hardness is a corresponding appropriately defined functional derivative η(r) = [δμ/δp(r)]v(r). Difficulties associated with ambiguities in this definition are discussed and resolved. It is concluded that for most purposes the best working formula for local hardness is , where η(r, r′) is the hardness kernel; , where F[p] is the usual Hohenberg-Kohn functional and f(r) is the Fukui function. With this definition, η(r) = η, a constant which is the global hardness. Just as the chemical potential equalizes in the ground state, so does the hardness. It is demonstrated that hardness can be taken to be an average of orbital contributions.  相似文献   

3.
Polyamideurethans of structures I and II were prepared by reacting N,N′-di-(6-hydroxycaproyl)alkylenediamines and N-hydroxyalkyl-6-hydroxycaproamide with hexa-methylene diisocyanate and 4,4′-diphenylmethane diisocyanate: where R1 is either a dimethylene or hexamethylene radical, and R2 is a hexamethylene or 4,4′-diphenylmethane radical. Polymers I and II were of a high degree of polymerization and crystallinity, had high enough melting points for practical use, and gave colorless tough films both by dry and melt castings. The polymers from hexamethylene diisocyanate were much more crystalline and thermally more stable above the melting points than those from 4,4′-diphenylmethane diisocyanate. Polymerization conditions and characteristic properties of the resulting polymers were studied.  相似文献   

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5.
Enantio‐ and diastereoselective inverse‐electron‐demand oxa‐Diels–Alder reactions are described between (Z)‐2‐ylideneoxindoles and aldehydes in the presence of a chiral secondary amine catalyst. The corresponding hydropyrano[3,2‐b]indoles are produced in up to 77% yield with up to 99% ee. Convenient synthetic transformations of the products readily lead to pharmacologically interesting scaffolds bearing multiple functional groups. This method may also provide an alternative approach for the asymmetric synthesis of 2‐spirocyclo‐3‐oxindoles.

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6.
The kinetics of anodic dissolution of gold in concentrated potassium cyanide solution was investigated. The mechanism was found to be with the second step being the rate determining step. Ultrasonic agitation increased the dissolution rate five-fold. The mechanism however, remained unchanged. From current efficiency measurement, it was observed that no auric ions existed in the dissolution process.  相似文献   

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A Brønsted acid, trifluoromethanesulfonimide [HN(SO2CF3)2], was found to catalyze reductive β‐alkylation of pyrroles with carbonyl compounds and hydrosilanes. This metal‐free process features lower catalyst loadings compared to the original indium variant and exclusive generation of β‐alkylpyrroles.

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Oligomeric stannoxanes having the general formula were prepared by treating amino and N-acylamino-acids with polymeric dibutyltin oxide at molar ratios less than 1. Shorter oligomers were built up to higher oligomers by insertion of dibutyltin oxide units.  相似文献   

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13.
The thermal decomposition of uranyl chloride hydrate has been investigated by thermal analyses, X-ray diffraction and infrared spectroscopy. From the results it is concluded that uranyl chloride hydrate decomposes thermally as follows: .  相似文献   

14.
Phosphate esters play important roles as biological active principles and synthons in chemistry. An efficient metal‐free approach for the synthesis of phosphate esters through sp3 C H activation is described. By using tetrabutylammonium iodide (Bu4NI) as a catalyst and tert‐butyl hydroperoxide (TBHP) as an oxidant, various toluene derivatives and phosphorus nucleophiles are tolerated in this transformation, affording the corresponding products in moderate to good yields.

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15.
Light absorption by the Fe(CN?)4?6 ion in aqueous solution at selected wavelengths between 214 and 313 nm results in the formation of excited states which yield the reaction sequence: with φe, the quantum yield, decreasing from 0.9 at the lowest to 0.1 at the highest wavelength. At and above 337.1 nm φe = 0. The role of charge transfer to solvent (CTTS) intermediates in this process is demonstrated. Photoaquation according to is found to have very low, possibly zero quantum yield in this region. The role of acid-base equilibria, e. g. and of the protonated species, in the photochemistry of cyanoferrate (II) species is discussed.  相似文献   

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17.
Linear Pfluger plots of unit slope are obtained from logarithmic rate constants for acid–catalysed hydration of phenylacetylene and its substituted derivatives p-OCH3, p-CH3, m-CH3, p-Br, m-Cl, m-NO2, p-NO2 in aqueous sulphuric acid solution. This direct experimental observation of absence of any dependence on selectivity gives evidence for the applicability of the kinetic acidity function in these systems.  相似文献   

18.
Azoacetoacetanilides condense with primary aliphatic amines to give azoaminocrotoanilides (I). Comparison of the infra-red and nuclear magnetic resonance spectra with those of model compounds leads to the proposal of formulae of type (VI) as a refinement of formula (I).   相似文献   

19.
Zinc‐catalyzed 1,4‐oxofluorinations of 3‐en‐1‐ynamides with Selectfluor in acetonitrile/water proceeded with high regio‐ and stereoselectivity, giving E‐configured γ‐fluoro‐α,β‐unsaturated amides efficiently. Our control experiments indicate that kinetically unstable C‐bound zinc dienolates are chemically reactive to undergo SE2′‐electrophilic fluorinations whereas the detectable O‐bound dienolates preferably undergo protodemetalation reactions instead.

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20.
A new synthetic method for α‐alkynyl‐α,β‐unsaturated esters is presented herein. The method is based on a copper(I)‐catalyzed three‐component reaction of a terminal alkyne, diazoesters and aldehydes. The reaction is featured by mild conditions, high yields and excellent stereoselectivity. Cu(I) carbene migratory insertion is proposed as the key step in the transformation.

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