摘要:

AbstractIn chemical research attention is increasingly being focussed on composite “complex” systems with special properties and functions. As components of such systems 1,4‐diazines are steadily gaining in popularity. Here, 1,4‐diazines means pyrazine and its derivatives as well as compounds with partial pyrazine structure; examples are quinoxaline, phenazine, pteridine, flavin and their derivatives. All these compounds are characterized by a low lying unoccupied π‐molecular orbital and by the ability to act as bridging ligand. Due to these two properties 1,4‐diazines, and especially their parent compound pyrazine, possess a characteristic reactivity. 1,4‐Diazines may be employed to study inter‐ and intramolecular electron transfer in organic, inorganic and biochemical reactions. In the redox system of 1,4‐diazines the paramagnetic 7π‐electron intermediate exhibits exceptional stability, whereas the 1,4‐dihydro‐1,4‐diazines with 8π‐electrons in a six‐membered ring are not generally accessible due to their potential antiaromaticity and their large excess of π electrons. Its inherent bifunctionality and the low lying unoccupied molecular orbital permit pyrazine to form coordination polymers having unusual electrical and magnetic properties. Finally, the phenomena observed for pyrazines may be used in the interpretation of the reactivity of naturally occurring 1,4‐diazines, such as flavins

ISSN:0570-0833    

DOI:10.1002/anie.198301713

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractDye diffusion instant color photography has been a commercial success ever since its introduction in 1963. No doubt this is partly due to the spectacular nature of this innovation, and for the same reason it has never really rid itself of its gadget image. Moreover, the picture quality was inferior to that of traditional color photography. Photographic materials are now available whose image quality approaches that of the traditional color print. It is not well known that chemistry, and organic chemistry in particular, is the cornerstone of these new photographic products. Insights from this field have spurred creativity, not only in the fields of dye and polymer chemistry, but above all in the search for more efficient and, hopefully better, dye diffusion transfer systems. The result of all these efforts is a finely tuned microscale chemical factory which continues to open rewarding perspectives for the photographic industry.

ISSN:0570-0833    

DOI:10.1002/anie.198301911

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe various electronic states in which molecules can exist are often considered to be independent. In this article we turn our attention to the limitations of this assumption, namely the interaction between different electronic states through the nuclear motion. This interaction can have several important consequences, two of which are discussed in some detail. One is a distortion of the molecular framework, leading to a lowering of the symmetry of a molecule in excited or ionic states compared to the neutral ground state. General aspects of this symmetry lowering are outlined and interpreted with the aid of typical examples. The other consequence considered is the ability of the nuclei to “jump” between different molecular potential energy surfaces (non‐Born‐Oppenheimer effects). The nature of this behavior is analyzed and it is argued that the “jumping” can be very fast and efficient, dominating completely the nuclear motion. To exemplify our general ideas we refer to the photoelectron spectra of ethylene and related compounds and demonstrate that they are governed by strong non‐Born‐Oppenheimer effects. It emerges that the Franck‐Condon principle fails in the analysis of their v

ISSN:0570-0833    

DOI:10.1002/anie.198302101

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe temperature dependence of the rate of chemical reactions has been known for a long time; very often it is characterized by the Arrhenius plot. However, kinetic methods that take this phenomenon into account in one measurement in a planned manner have been applied to reactions in solution only in isolated examples‐with the exception of the temperature jump method developed by Eigen et al. for fast reactions, based on a stepped temperature program. A mathematical analysis, however, reveals to the chemist that from the point of view of information theory the course of the reaction rate versus time under conditions of constantly increasing temperature is the measured signal which should lead to the most effective understanding of the reaction mechanism. Analysis of the measured peaks, which may overlap, allows the characterization of reactions either in the solid state or in solution by “mechanistic coordinates”, which extend the concept of reaction order. Their behavior allows further experiments to be planned, enabling elementary steps to be eliminated. Each reacting system can be characterized kinetically by one series of experiments using different starting concentrations for each reactant and additionally, using different heating rates. The experimental verification of these considerations can be seen inca. 1400 DTA and UV experiments forca. 120 different systems. Furthermore, the example of the oscillating Belousov‐Zhabotinsky reaction shows that “fast” reactions frequently may also be recognized. A test for proposed reaction mechanisms is provided by integration programs which allow immediate comparison between experimental and theoretical si

ISSN:0570-0833    

DOI:10.1002/anie.198302251

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe complete manuscript of this communication appears in:Angew. Chem. Suppl. 1983, 282. DOI:10.1002/anie.198302820

ISSN:0570-0833    

DOI:10.1002/anie.198302411

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe complete manuscript of this communication appears in:Angew. Chem. Suppl. 1983, 288. DOI:10.1002/anie.198302880

ISSN:0570-0833    

DOI:10.1002/anie.198302421

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe complete manuscript of this communication appears in:Angew. Chem. Suppl. 1983, 299. DOI:10.1002/anie.198302990

ISSN:0570-0833    

DOI:10.1002/anie.198302431

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

摘要:

AbstractThe complete manuscript of this communication appears in:Angew. Chem. Suppl. 1983, 222. DOI:10.1002/anie.198302220

ISSN:0570-0833    

DOI:10.1002/anie.198302441

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198302451

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198302462

出版商:Hüthig&Wepf Verlag    

年代:1983

数据来源: WILEY