摘要:

AbstractThe localized molecular orbitals (LMOs) of certain quasi‐aromatic organic and inorganic molecules with six‐membered rings have been calculated by virtue of theab initiomethod using STO‐3G and 4–31G basis sets as well as the CNDO/2 method. It is shown that there exists extensively‐delocalized p‐pπ bonding in these quasi‐aromatic systems. The localized pictures of the π‐type LMOs for the heterocyclic and homocyclic systems from the σ‐π localization scheme are discussed. The Generator Orbital approach is utilized to account for

ISSN:1001-604X    

DOI:10.1002/cjoc.19930110601

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY

摘要:

AbstractA modern valence bond approach, namely bonded tableau unitary group approach, is applied to ozone, sulphur dioxide and nitrite systems, respectively. It is shown that the biradical structure is in the primary position in describing the molecular structure of ozone. Thus three instead of two resonance structures are needed to describe the ground state of ozone. The case of sulphur dioxide is similar to that of ozone. It is found that, however, for the nitrite anion four resonance structures are needed.

ISSN:1001-604X    

DOI:10.1002/cjoc.19930110602

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY

摘要:

AbstractThe classical theory of the rate of unimolecular isomerization developed by Gray and Rice as extended by Zhao and Rice is applied to the calculation of the rate of isomerization in model systems which have linear asymmetric double well potentials. We are interested in this system for two reasons. First, we are interested in the detailed dynamical processes for the mentioned system because it is widely related to practical chemical reactions. Second, the present model system has an asymmetric double well potential, which provides a different test of the accuracy of the approximations used in the Gray‐Zhao‐Rice theory than posed by previous applications. We have calculated relaxation rates and relaxation times for the model systems on different time scales. We find that for the systems under studies the Gray‐Zhao‐Rice version of the classical theory of isomerization rate yields values in good agreement with those generated from trajectory calculations and from the Reactive Island theory of De Le

ISSN:1001-604X    

DOI:10.1002/cjoc.19930110603

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY

摘要:

AbstractNickel‐substituted saponite clays (NiS) were synthesized. The pillared clays noted PNiS were prepared from the NiS intercalated with large inorganic cations such as [Al13O4(OH)24·(H2O)12]7+. It is found that the pillar density is correlative with aluminium content in the tetrahedral sheet of NiS. The results from TPR indicate that the palladium loaded on samples promotes the reduction of the nickel ion in the octahedral sheet. The pillared clays impregnated with Pd2+noted PdPNiS show excellent hydroisomerization property which is much better than that of nickel substituted mica‐montmorillonite pillared with silicon oxide oligomer noted PdPSMM. The hexane conversion increases with the content of aluminium ion in the tetrahedral sheet, whereas the change of the selectivity of isomerization is not obv

ISSN:1001-604X    

DOI:10.1002/cjoc.19930110604

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY

摘要:

AbstractThe reation between [Ru3(CO)9(CCO)]2−supported on magnesium oxide and alkylating agent CH3I was investigated in an attempt to understand its reactivity and mechanism by using FT‐IR technique. The IR spectra show that [Ru3(CO)9(CCO)]2−/MgO reacts with CH3I to produce [Ru3(CO)9CC(O)CH3]−/MgO, which exhibits bands at 2960, 2022, 1988, 1638, 1460 and 1350 cm−1. The absorption at 2960, 1460 and 1350 cm−1are attributed to ‐CH3group, while bands at 2022, 1988 and 1952 cm−1are assigned to the terminal CO groups attached to ruthenium. The band at 1638 cm−1was assigned to acyl carbonyl. Isotopes labeled compounds CD3I,13CO and [Ru3(CO)9(*C*CO)]2−were used in investigation. The results demonstrate that β‐carbon of CCO ligand is attacked by CH+3species and produces [

ISSN:1001-604X    

DOI:10.1002/cjoc.19930110605

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY

摘要:

AbstractUpon addition of Tb3+to 16 nucleotides and homopolynucleotides, all of them showed a characteristic green emission from Tb3+, but with much different intensity, upon excitation in the aromatic region of bases. The result suggested that nucleotides with at least one carbonyl group in nucleotide bases are better enhancers to the fluorescence of Tb3+. The complexes of ATP, GDP and GTP with Tb3+are synthesized as two types of models. Guanine type nucleotides with one carbonyl group in the bases are the best enhancers, while adenine type nucleotides with no carbonyl group in the bases are poorest enhancers to the fluorescence of Tb3+. Comparing the IR spectra of ATP, GTP, GDP and their Tb3+complexes suggested that C‐6 carbonyl group in GTP and GDP may be involved in complex formation, which may be responsible for the effective energy transfer. This is further supported by comparing the UV spectra of ATP, Poly(A), GTP, and Poly(G) with their Tb3+complexes in water solutio

ISSN:1001-604X    

DOI:10.1002/cjoc.19930110606

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY

摘要:

AbstractThe complexation of HA (or HB) with bivalent metals was examined by UV‐Vis and NMR spectroscopy, and all of the complexes obtained have a metal‐ligand ratio of 1:1. The photoinduced reduction of the complexes of HA‐Zn2+and HA‐Mg2+(or HB‐Zn2+, HB‐Mg2+) in the presence of 1‐benzyl‐1,4‐dihydro‐nicotinamide as the electron donor was investigated by UV‐Vis and ESR spectroscopy. The studies demonstrated that illumination of the complexes of HA(HB)‐Zn2+and HA(HB)‐Mg2+led to the accumulation of the chelated s

ISSN:1001-604X    

DOI:10.1002/cjoc.19930110607

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY

摘要:

AbstractFast atom bombardment mass spectrometry (FAB‐MS) is applied to distinguishN‐terminal series ions fromC‐terminal series ions of a peptide by on‐probe acetylation, it provides valuable information about the sequence of an unknown peptide. The FAB mass spectra contain a number of characteristic ions at low‐mass region in addition to the sequence ions at high‐mass region. It was found that the ions belowm/z200 are characteristic of the amino acid composition of the peptide, from which the amino acid composition of the peptide could be estimated. Additionally, mixture analysis is als

ISSN:1001-604X    

DOI:10.1002/cjoc.19930110608

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY

摘要:

AbstractThe possibility of ion flotation of cerium subgroup rare earths (Ce‐subgroup), was explored. Various factors affecting the. flotation efficiency were investigated. The results showed that, by using sodium tetradecyl sulfate as the collector of trace Ce‐subgroup and frother, over 95% of Ce‐subgroup at ng/g levels could be separated from pH 2.3 media in 10—15 min. The proposed method has been applied to the determination of Ce‐subgroup in a polluted farmland soil reference material (GBW 08303) with satisfactor

ISSN:1001-604X    

DOI:10.1002/cjoc.19930110609

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY

摘要:

AbstractIn order to investigate the mechanism of mercuration reaction of substituted benzylideneanilines, kinetic measurements of these reactions at different temperatures (40–60° C) in methanol‐1,4‐dioxane (1/1,V/V) were carried out and Hammett ρ value forC‐phenyl substituents of −0.61 for theN‐(substituted benzylidene)‐4‐toluidine series was obtained. Thermodynamic parametersE3ΔS# were obtained for the reaction of differentN‐(substituted benzylidene)‐4‐toluidines. It was found that thisortho‐mercuration was brought about by an internal cyclometallation process

ISSN:1001-604X    

DOI:10.1002/cjoc.19930110610

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA, Weinheim    

年代:1993

数据来源: WILEY