摘要:

AbstractThe coordination number of sulfur is used in this review as a classification principle; cyclic sulfur‐nitrogen compounds in which the sulfur is di‐, tri‐, and tetracoordinated are discussed. Compounds with sulfur (and nitrogen) of coordination number 2 are electron‐rich combinations of elements whose π‐electrons are extensively delocalized. A correlation between the coordination number and the bond length can be observed in certain compounds containing tri‐ and tetracoordi

ISSN:0570-0833    

DOI:10.1002/anie.197900913

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractAlthough the effect of solvent on the rate and the position of equilibrium of chemical reactions has been known since the last century, there are still no reliable and exact methods for a quantitative description and prediction of such solvent effects. Empirical parameters of solvent polarity are of great value in this respect and can be derived with the aid of the principle of “linear relationships between free energies” (LFE relationships). The present article deals with the possibilities of establishing reaction and absorption series using solvent‐dependent standard reactions or standard absorptions of organic compounds. Particular attention is merited by the summary of the 24 most important empirical parameters of solvent polarity and the table ofET(30) values for 151 solvents. In addition to examples of the application of these values, attempts to improve the LFE correlations of singular empirical parameters of solvent polarity with the aid of multiparametric equations are desc

ISSN:0570-0833    

DOI:10.1002/anie.197900981

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractThe mathematical model of constitutional chemistry described here is based on a concept of isomerism which has been extended from molecules to ensembles of molecules. A chemical reaction is the conversion of an ensemble of molecules into an isomeric ensemble. An ensemble of molecules is representable by an atomic vector and an associated bond and electron (BE)‐ matrix, and a reaction by a reaction (R)‐matrix. These BE‐and R‐matrices serve as a basis for computer programs for the deductive solution of chemical problems. We present here algorithms and computer programs based on the theory of BE‐ and R‐matrices. They enable the classification and documentation of structrues, substructures and reactions, the prognosis of reaction products,the design of syntheses, the construction of networks of mechanistic and synthetic pathways and the prediction of chemica

ISSN:0570-0833    

DOI:10.1002/anie.197901111

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractActivation analysis is one of the most important methods available for the determination of traces of elements and of isotopes. One special advantage of activation analysis is its ability to cope with the simultaneous determination of many elements with very high detection sensitivity–for many elements lying below the ppb level. In some cases as little as 10−14—10−15g of an element can be detected. A number of sources of systematic errors common to other analytical procedures, mainly those caused by the blank, are eliminated in activation methods. The disadvantages may be seen as the inconvenience of handling radioactive materials, the dependence on large irradiation facilities, and sometimes the unavoidably long irradiation and cooling periods. On account of its unique capabilities activation analysis finds applications in all fields of endeavor where minute amounts of elements are of significance, from materials research through medicine to archaeology. Further improvements in performance and increases in scope are seen to lie in the development of new radiation sources, activation techniques, measurement systems, and separation pro

ISSN:0570-0833    

DOI:10.1002/anie.197901231

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197901471

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197901481

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197901491

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197901501

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197901511

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197901521

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY