摘要:

AbstractMost of the industrial plastics used up to now consist of flexible macromolecules in which the repeat units are joined together in a nonlinear fashion by rotating bonds. Stiff‐chain polymers, which in the ideal case have a rodlike shape, have received much less attention. The reason for this is that such polymers usually exhibit an exceedingly low solubility. Very often, they are absolutely insoluble and do not melt. However, in recent years these polymers have aroused technical interest because high‐modulus fibers and moldings can be fabricated from them. These favorable mechanical properties are directly related to the nearly parallel arrangement of the rodlike macromolecules in the solid state which is achieved through spinning or extrusion from a liquid crystalline (nematic) state. It is therefore evident that a thorough understanding of the phase behavior and the structure is required for a universal technical utilization of these materials. The great variety of methods used in polymer science today has led to a deeper understanding of stiff‐chain polymers. Experimental results together with theoretical modeling of the phase behavior have direct implications for the practical use of these macromolecular mate

ISSN:0570-0833    

DOI:10.1002/anie.198902533

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractQuantum mechanical and classical aspects are of equal importance in chemistry, and theoretical chemistry must be able to deal with this situation. Classical quantities with which a chemist has to deal include, for example, the temperature and the chemical potential of a substance, and chirality, knot‐type and tertiary structures of molecules. Classical concepts of this type are no more consequences of traditional quantum chemistry than is the theory of complex chemical processes (for example adsorption, heterogeneous catalysis) and macroscopic systems. Algebraic quantum mechanics affords a general framework for the discussion of classical quantities and large systems. There are other independent approaches for the theoretical treatment of chemical problems; these can be summarized by using the keywords “fractals”, “chaotic motion”, “quasicrystals” and “knot theory”. The relationships between these four research topics and their connection with algebraic quantum mechanics, as well as their importance for theoretical chemistry, were discussed at a NATO Workshop in 1987 (see Ref. [1]). In an extended theoretical chemistry, the notion of “molecules” will not play a role as central as it does in quantum chemistry. In the theory of large systems in particular, the introduction of complementary approaches appears to be appropriate; the term “molecule” as used by the chemist does not appear either in the description of disordered systems by means of fractals or in the thermodynamic limit of algebr

ISSN:0570-0833    

DOI:10.1002/anie.198902681

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractAcceptor‐substituted lithio compounds LiACR1R2, in which the acceptor A is an RC(0), NC, RSO2, RS(O)NR, RSO, RS, O2N, or RC(NNR2) group, have long played an important role in organic synthesis. Their significance has grown still further in the last fifteen years, as one has increasingly learnt to employ them successfully in chemo‐, regio‐, diastereo‐and enantioselective reactions. Remarkably, little if anything was known of the structures of these compounds. It is therefore not surprising that interest in the structures of this class of compounds has greatly increased in recent years. In the following review, we shall summarize recent research into the structures of the lithio compounds of sulfones, sulfoximides, sulfoxides, thioethers and 1,3‐dithianes, nitriles, nitro compounds, and hydrazones. Crystal structure determinations from recent years are central to this study. They are supplemented by solution studies and by calculations of structures. Structural similarities and differences between the individual states of aggregation are pointed out wherever possible, as is also the relationship between structure

ISSN:0570-0833    

DOI:10.1002/anie.198902771

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198902981

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198903001

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198903031

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198903051

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198903101

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198903131

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198903151

出版商:Hüthig&Wepf Verlag    

年代:1989

数据来源: WILEY