摘要:

AbstractThe general concept of carbocations encompasses all cations of carbon containing compounds which can be differentiated into two distinct classes: trivalent (“classical”) carbenium ions and pentacoordinated (“nonclassical”) carbonium ions. In this paper the preparation and structural study (by NMR, IR, Raman and ESCA spectroscopy) of stable carbenium ions and carbonium ions are discussed. As is well known, trivalent carbenium ions play an important role in electrophilic reactions of π‐ and n‐donor systems. Similarly, pentacoordinated carbonium ions are the key to electrophilic reactions of σ‐donor systems (single bonds). The ability of single bonds to act as σ‐donor lies in their ability to form carbonium ionsviatriangular two electron, three‐center bond formation. Consequently there seems to be no principle difference between the electrophilic reactions of π‐ and σ‐bonds except that the former react more easily, even with weak electrophiles, whereas the latter necessitate more severe conditions. The role of carbocations in electrophilic reactions of π‐ and

ISSN:0570-0833    

DOI:10.1002/anie.197301731

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY

摘要:

AbstractCycloadditions with ionic components are known as “polar cycloadditions” to distinguish them from cycloadditions with dipolar and uncharged components. The structural requirements, the manner in which “polar” intermediates capable of addition are produced and their reactivity with activated and nonactivated multiple bonds, the many peculiarities of the course of the cycloaddition, and the favorable synthesis of heterocyclic systems by this reaction principle makes such a terminological distinction useful and necessary if the existing data are to be brought into order. The present review, which is the first on a field of chemistry that has not yet been very extensively investigated, deals initially with cationic and then with anionic polar cycload

ISSN:0570-0833    

DOI:10.1002/anie.197302121

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY

摘要:

AbstractAzo compounds are characterized by a low‐energy1(n,π*) electronic state, which gives rise to a weak band at long wavelengths in the absorption spectrum. Coupling of this state with other low‐lying molecular states is responsible for the high intensity of the “azo band” compared to other forbidden transitions, for its lack of vibrational structure, and for the inability of nearly all organic azo compounds to f

ISSN:0570-0833    

DOI:10.1002/anie.197302241

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197302351

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197302361

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197302372

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197302381

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197302391

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197302401

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197302411

出版商:Hüthig&Wepf Verlag    

年代:1973

数据来源: WILEY