摘要:

AbstractThe nitrogen nucleus is the third most important probe (after1H and13C) for structural investigations of organic and bioorganic molecules by NMR spectroscopy. For a long time, however, the insufficient sensitivity and low natural abundance of the15N isotope hampered detection of the15N nucleus, and the quadrupolar14N nucleus proved unsuitable for the study of larger molecules with several nonequivalent nitrogen atoms. The advent of new techniques, such as pulse sequences and polarization transfer, in conjunction with the use of high‐field magnets and large‐sample probe heads largely solved the detection problem. As a result, the last few years have seen a dramatic development of15N‐NMR spectroscopy as a versatile method for studying molecular structure, both in isotropic (liquid) and anisotropic (solid) phases. The scope of chemical applications extends from inorganic, organometallic, and organic chemistry to biochemistry and molecular biology, and includes the study of reactive intermediates, biopolymers, enzyme‐inhibitor complexes, and nitrogen metabolism. Two‐dimensional NMR techniques offer additional possibilities for detailed studies of biologica

ISSN:0570-0833    

DOI:10.1002/anie.198603833

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractThe preference for carrying out synthetic organic reactions at the lowest possible temperature is due to the expectation that the selectivity often increases with decreasing temperature, as is confirmed by many examples and also theoretically justified. Selectivity, however, is not the only problem at high temperatures; further factors include the frequently limited thermal stability of the functional groups and structural elements not directly involved in the transformation. In spite of these limitations, the advantages of high temperatures and the greatly improved knowledge of the mechanisms of dynamic gas‐phase processes accumulated in recent years can be exploited in directed organic synthesis. In this review the synthetic potential of gas‐phase flow thermolysis will be described from the viewpoint of the synthetic chemist with the aid of typical examples of applicat

ISSN:0570-0833    

DOI:10.1002/anie.198604141

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractThe pentagonal column (PC), consisting of MX7bipyramids sharing their equatorial edges with five MX6octahedra, is a structural feature frequently occurring in association with frameworks of the ReO3‐type, where it enables accomodation of an anion deficiency. The present article discusses the geometry of the PC and its compatibility with the ReO3‐type structure, which naturally emerges from the finding that a PC may result from twinning of an ReO3‐type structure on the unit cell level. A new symbolism is presented which facilitates visualization of a large variety of crystal and defect structures of MX3–xstoichiometry. This symbolism may also serve as a convenient aid in deriving models of possible new structures that may be of value in the interpretation of HREM

ISSN:0570-0833    

DOI:10.1002/anie.198604311

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198604431

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198604441

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198604461

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198604471

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198604491

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198604501

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198604511

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY