摘要:

AbstractAddition compounds of Lewis acids MXnand acyl halides RCOX occur as intermediates in Friedel‐Crafts acylations. IR and NMR studies on these intermediates have indicated the probable existence of structural isomers. In X‐ray structural analysis, it is possible to distinguish two forms,i.e.the molecular form, in which the compounds are present as donor‐acceptor complexes RCXO→MXn, and the ionic form, in which they can be formulated as oxocarbenium salts [RCO]+[MXn+1]−. The compounds of the donor‐acceptor type RCXO→MXnare characterized by the formation of a coordinate oxygen‐metal bond; the transfer of electrons from the oxygen to the metal of the acceptor is always due to a weak donor‐acceptor interaction. The positive charge of the aryloxocarbenium ions is partly delocalized over the aromatic nucleus. The positive charge in alkyloxocarbenium ions, on the other hand, is essentially localized on the carbon atom of the carbonyl group, as is confirmed by electron density

ISSN:0570-0833    

DOI:10.1002/anie.197400011

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY

摘要:

AbstractThe natural inhibitors of proteolytic enzymes are proteins. These inhibitors associate reversibly with the enzymes to form stoichiometric protein‐protein complexes, in which substrate‐analogous association at the active center of the enzyme results in competitive inhibition of all catalytic functions. The very widespread occurrence of inhibitors in the animal and plant kingdoms underlines their biological importance in the intermediate metabolism, which can be understood as an extension of the possibilities for temporary and local limitations of enzyme activities. Existing knowledge includes a series of covalent structures, detailed kinetic data on the reversible protein‐protein interaction, the processes involved in inactivation, and chemical methods for the modification of these proteins. Early X‐ray structural data for an inhibitor and its enzyme complex provide an insight into the molecular structure of the latter and the interactions involved in the association to form the

ISSN:0570-0833    

DOI:10.1002/anie.197400101

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY

摘要:

AbstractMolecular oxygen as a ligand in transition metal complexes is of interest for biochemistry, and for inorganic and organometallic chemistry. Several examples of O2complexes, as well as the kinetics and mechanism of their formation are presented. The influence of other ligands on the activation of O2is discussed on the basis of a MO description of the electronic structure of the oxygen molecule and of the bonding within the metal‐oxygen complexes. Reactions of coordinated oxygen are describe

ISSN:0570-0833    

DOI:10.1002/anie.197400291

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY

摘要:

AbstractVery high pressure is becoming increasingly important for investigating electronic structure. The relative shift in energy of electronic orbitals which is commonly observed at high pressure can frequently lead to a new ground state for the system. These electronic transitions may result in changes in electrical, optical, or magnetic properties as well as changes in chemical reactivity. Electronic transitions in metals and insulator‐metal transitions have been widely studied by physicists. Recently, it has been found that electronic transitions in aromatic hydrocarbons and their electron donor‐acceptor complexes can induce chemical reactivity and lead to the formation of new classes of hydrocarbons.Electronic transitions in transition metal complexes may lead to changes in spin state; both increase and decrease in multiplicity with increasing pressure have been observed. In addition, it has been shown that Fe(III) and Cu(II) reduce at high pressure in a variety of compounds. The behavior of these transition metal ions is described in some detail in relation to the general area of high pressure and electronic struct

ISSN:0570-0833    

DOI:10.1002/anie.197400391

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY

摘要:

AbstractThe six‐electron thermal pericyclic reactions are examined systematically as to the number and kind which are possible by varying both the σ shell and the combinations of different atoms in all orientations, on both a six‐atom and a five‐atom framework. A simple unifying nomenclature is offered for these reactions, which number in the thousands. Further, in order to comprehend this very large number of possible reactions, they are also organized systematically in terms of their value for basic synthesis operations: construction, elimination, refunctionalization, etc. The methodology is aimed at providing a basis of selection for the invention of useful new reactions. A discussion of reaction energetics leads also to an analysis of molecular features which can facilitate re

ISSN:0570-0833    

DOI:10.1002/anie.197400471

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197400772

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197400791

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197400801

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197400811

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197400821

出版商:Hüthig&Wepf Verlag    

年代:1974

数据来源: WILEY