摘要:

AbstractEffective syntheses employing 2‐halogenated pyridinium, benzoxazolium, benzothiazolium, and pyridinium salts have been accomplished in the absence of strong acids and bases. Activation of carboxylic acids or alcohols with these onium salts leads to 2‐acyloxy and 2‐alkoxy intermediates which can be transformed into esters, amides, thiol esters, (macrocyclic) lactones, acid fluorides, olefins, allenes, carbodiimides isocyanates, isothiocyanates, nitriles, and isocyanates. The possibility of performing stereospecific syntheses (involving configurational inversion) with onium salts deserves atte

ISSN:0570-0833    

DOI:10.1002/anie.197907073

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractThe 1,3‐dipolar cycloreversion reaction represents a general scheme of fragmentation of pentaatomic heterocycles to produce 1,3‐dipolar systems and dipolarophiles. This review summarize cycloreversions which give rise to octet‐stabilized 1,3‐dipoles. The reaction can be either thermal or photochemical or electron impact induced. The aim of the article is to survey the published results, to emphasize the synthetic potential of this reaction, and to stimulate the study of its several not yet unambiguously defined mechanistic

ISSN:0570-0833    

DOI:10.1002/anie.197907211

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractAlthough it has been recognized for many years that the spectra of lanthanoid ions can provide useful information about short range phenomena in the neighborhood of these inos in a solid material, lanthanoid spectroscopy has only infrequently been used for studying complex materials because of the problem of line‐sorting the complex spectra that are obtained. The advent of convenient tuneable lasers has eliminated this problem. Byselectivelyexcitingprobeionluminescence (SEPIL), it is possible to obtain fluorescence and excitation spectra from a single kind of crystallographic environment. Two applications of this method are dicussed in this paper. The first application is the study of the defect chemistry of fluorite materials (compounds with CaF2lattice). It is shown how this method can provide unique information about the solid state chemistry, thus clarifying many of the unexplained behaviors of this important class of material. The second application shows application shows how ultra‐trace analysis can be carried out by causing an association between an analyte ion and a fluorecent probe ion. The unique crystal field levels of a probe ion associated with a particular analyte can be selectively excited so that traces of the ion to be analyzed can be detected with very high selectivity and with very low detection lim

ISSN:0570-0833    

DOI:10.1002/anie.197907381

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY

摘要:

AbstractThe properties of cyclic crown ethers are approximated by acyclic neutral ligands (popdands), which are compared and contrasted with open‐chain bioionophores and acidic chelating agents in this article. Variations of theendo‐polarophilicity/exo‐lipophilicity balance, complex stability, ion slectivity can often be accomplished more easily, with greater versatility, and at less expense with acyclic polyethers than with their cyclic counterparts; complexation and decomplexation are generally faster in acyclic systems; and the pseudocavity usually has greater conformational flexibility. Acyclic crown ethers and open‐chain cryptands stiffened by rigid “terminal groups” containing donor atoms readily form crystalline complexes of alkali and alkaline earth metals. Some oppen‐chain neutral ligands form helical conformations in their crycstalin complexes. The observed coordination numbers and geometries are of theoretical interst. Attractive terminal group interactions lead to pseudocyclic species occupying a position intermediate between cyclic and acyclic ligands. It has recently proved possible to isolate crystalline complexes of alkali and alkaline earth metal ions with weakly donating oligo(ethylene glycol ethers) and with glycols; such complexes have also been obtained with sugars. Acyclic neutral ligands can serve as simple models of nigericin‐type bioionophores and be used analytically in microelectrodes. The recently discoverd crystalline stoichiometric complexes formed by some acyclic neutral ligands with guest molecules such as urea, thiourea, and water provide a fresh insight into weak interactions between neutral molecules and for the development of

ISSN:0570-0833    

DOI:10.1002/anie.197907531

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197907771

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197907781

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197907791

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197907801

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197907811

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.197907821

出版商:Hüthig&Wepf Verlag    

年代:1979

数据来源: WILEY