摘要:

AbstractStructure, a necessary element for an understanding of chemistry, has not been precisely defined, in molecular detail, for the surface species formed at a solid‐gas interface. Dramatic advances in theory, instruments and experimental procedures have now provided the surface scientists with an impressive arsenal of structural and electronic probes. Chemistry in the form of the classic displacement reaction can also provide an insight to the structure of surface compounds. In fact, many of the experimental procedures and systematics of the coordination and organometallic chemist can be effectively utilized in a complementary fashion with surface physics techniques to gain a more definitive picture of chemisorption states and or reactions at a surfac

ISSN:0570-0833    

DOI:10.1002/anie.197805453

出版商:Hüthig&Wepf Verlag    

年代:1978

数据来源: WILEY

摘要:

AbstractSpiro compounds having mutually perpendicular π‐electron systems (“spiro‐polyenes”) exhibit a new kind of homoconjugation, which is designated as spiroconjugation. Spiro‐polyenes are readily accessible,e.g.by cycloaddition, by elimination of dinitrogen from 1,2‐diazaspiro‐polyenes, and by cyclization of carbenium ions or carbanions. The magnitude of the effect exerted by spiroconjugation is estimated by model calculations. It can be detected, for instance, by comparison of the electronic and photoelectron spectra of spiro‐polyenes and analogous compounds which are unable to undergo

ISSN:0570-0833    

DOI:10.1002/anie.197805591

出版商:Hüthig&Wepf Verlag    

年代:1978

数据来源: WILEY

摘要:

AbstractThe synthesis of 4‐dialkylaminopyridines can be accomplished in two steps starting from pyridine. Compared to pyridine, these derivatives are approximately 104times more active when used as acylation catalysts. Dialkylaminopyridines are being used with ever‐increasing frequency for acylation reactions which proceed either incompletely or not at all in pyridine. This article reviews the various possible applications of 4‐dialkylaminopyridines in terpene, steroid, carbohydrate and nucleoside chemistry as well as in the transformation of amino acids into α‐acyl aminoketones and polymerization of isocyanates. In addition,N‐substituted 4‐dialkylaminopyridinium salts can be used for the transfer of sensitive groups to nucleophiles in aqueous medium. The exceptional catalytic effect of these derivatives, even in non‐polar solvents, is due, in part, to the formation of high concentrations ofN‐acylpyridinium salts which are present in solution as loosely‐bound, highly

ISSN:0570-0833    

DOI:10.1002/anie.197805691

出版商:Hüthig&Wepf Verlag    

年代:1978

数据来源: WILEY

摘要:

AbstractThe presence of histidine in the active center of an enzyme can be demonstrated by kinetic measurements, chemical modification, NMR spectroscopy or X‐ray structure analysis. Histidine is the only naturally occurring amino acid to contain an imidazole residue as a side chain. The role of histidine in enzyme catalysis depends,inter alia, upon the special features of the imidazole residue: it thus tends to form hydrogen bonds, combines donor and acceptor properties and can take part in either nucleophilic or base catalysis. In some of these enzymes the position of each atom is known; however, the theories as to how the catalysis proceeds at a molecular level are controversia

ISSN:0570-0833    

DOI:10.1002/anie.197805831

出版商:Hüthig&Wepf Verlag    

年代:1978

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197805931

出版商:Hüthig&Wepf Verlag    

年代:1978

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197805941

出版商:Hüthig&Wepf Verlag    

年代:1978

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197805951

出版商:Hüthig&Wepf Verlag    

年代:1978

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197805961

出版商:Hüthig&Wepf Verlag    

年代:1978

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197805971

出版商:Hüthig&Wepf Verlag    

年代:1978

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197805981

出版商:Hüthig&Wepf Verlag    

年代:1978

数据来源: WILEY