摘要:

AbstractToday's textbooks convey the deceptive impression that chemistry developed in a rational and orderly process with discoveries following one upon another in a vertical progression—an impression that tends to classify Fischer's achievement as a matter‐of‐fact historical development. This misconception does not consider the instances of serendipity invariably involved, and entirely fails to appreciate the human endeavor, the intellectual struggle of the dedicated researcher, and the forging force of his personality that eventually led to this key insight. The hundredth anniversary of Fischer's classical piece of work provides a welcome opportunity not only to highlight its paramount importance for the development of carbohydrate chemistry, and of organic chemistry in general, but to trace the creative processes underlying this fundamental discovery, the thought patterns at a conceptual level, and the constructive reasoning that eventually led to it. Their understanding and appreciation is essential for emulating Fischer's achievement in a modern context.Die Geschichte einer Wissenschaft ist diese Wissenschaft selbst, J. W. von

ISSN:0570-0833    

DOI:10.1002/anie.199215413

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractNeutron diffraction studies, especially with powders, play an important role in structural solid‐state chemistry, making possible the precise determination of the location of light atoms, particularly hydrogen, and enabling a distinction to be made between certain neighboring elements in the periodic table that are difficult to distinguish in experiments with X‐rays. Neutron diffraction investigations also make a unique contribution in the area of magnetic structure determination. The availability of intense synchrotron X‐rays sources, however, is opening up new opportunities to the structural chemist, many of them complementary to the “traditional” strengths of neutron methods. The key features of synchrotron radiation in relation to structural studies are the wavelength tunability, which facilitates the use of resonant diffraction methods, and the high brightness and excellent vertical collimation of the source, which make possible the construction of diffractometers with unparalleled angular and spatial resolution. The following types of experiments are now possible with synchrotron X‐ray diffraction: (1) The ab initio determination of structures from powder diffraction data. (2) The differentiation between different oxidation states of an element (valence contrast experiments) based upon the sensitivity of an absorption edge to the valence of the element in question. (3) The differentiation of elements adjacent to each other in the periodic table, which is now feasible with synchrotron X‐rays for all elements beyond chromium. (4) Site‐selective X‐ray absorption spectroscopy. (5) The study of cation occupancies in materials where more than one element occupies a site that is, or may be, partially occupied. (Such problems are important in zeolite chemistry and high‐temperature superconductors.) (6) The determination of crystal structures from microcrystals. (7) In situ and rapid, time‐resolved diffraction studies. This review examines the roles played by X‐ray and neutron diffraction studies in modern solid‐state chemistry, and describes some recent examples in which the use of neutron radiation or synchrotron X

ISSN:0570-0833    

DOI:10.1002/anie.199215571

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199215711

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199215771

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199215781

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199215831

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199215851

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199215871

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199215881

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.199215921

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY