摘要:

AbstractThe diluted gas phase within a mass spectrometer is ideally suited for performing collision experiments of fast moving ions with thermalized target atoms. One important reaction which can be brought about with a given cation is its selective reduction, i. e. its neutralization. This allows the synthesis in tailored experiments of a variety of unusual chemical species, which because of intermolecular processes cannot be prepared or studied in solution or in a matrix. Among the molecules which have been generated in this way are hypervalent species (Rydberg radicals) like H 3⊙, van der Waals complexes like He2, mono‐ or disubstituted acetylene derivatives XCCY (X  H, Y  OH, NH2; X  Y  OH, NH2), and elusive compounds like carbonic acid (H2CO3) or carbamic acid (NH2CO2H). Collision experiments can also be used advantageously for the structural analysis of theneutral molecule Ngenerated in unimolecular dissociation reactions of the typem 1⊕→m 2⊕+N. The dissociation of ionized aniline for example yields, besides C5H 6⊙⊕cations, neutral isocyanic acid, HNC, and not cyanic acid, HCN. The technique ofNeutralization Reionization Mass Spectrometry(NRMS) is performed in the diluted gas phase, a medium where intermolecular interactions are entirely absent. The method may therefore increasingly be applied to the study of molecular species whose reactivity precludes their characterization in matrices. Molecules in specific excited states and fragments of organometallic compounds with unsaturated valencies are two examples of systems wh

ISSN:0570-0833    

DOI:10.1002/anie.198708053

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractThe liquid crystalline behavior of low molecular weight compounds has been known for more than a century; synthetic polymers have been manufactured on a large scale for several decades, but just recently it was found possible to produce polymers using the structural principles of liquid crystalline compounds. The resulting materials have, as expected, unusual properties. Numerous applications, not only in opto‐electronics, are already anticipated for such material

ISSN:0570-0833    

DOI:10.1002/anie.198708161

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractBimolecular photoreactions usually occur via several steps involving “complex‐type” intermediates (excimers or exciplexes). Although physical chemists have investigated them for nearly thirty years (Förster, Weller), and postulated their existence in numerous publications, it is only in the last decade that evidence for an exciplex intermediate in cycloadditions (Caldwell) has been obtained, thereby establishing the link between spectroscopy and synthetic photochemistry. Since then, many investigations have confirmed the role of exciplexes as intermediates in bimolecular photoreactions. The photochemically induced charge transfer from a donor to an acceptor substrate determines not only the bond strengths in the primary exciplex but also influences—via the charge‐transfer nature of the complex—the structure of the exciplex and thereby the selectivity of subsequent reactions. Such chemical processes between the donor and the acceptor prevent the reverse transfer of electrons, which usually results in regeneration of the starting materials, thereby only causing the dissipation of energy and occasionally—under specific conditions—the generation of molecules of the starting material in the triplet state. Ionic photodissociation also reduces the probability of a reverse transfer of electrons. This process, which produces solvated radical ions, is promoted by polar solvents and salt effects, particularly special salt effects. By this means it is possible to generate specific radical cations from, for example, alkenes and dienes and to study their reactions. Although in some areas, for example physical and biophysical chemistry, discussions of single electron transfer (SET) processes have long been found in the basic textbooks, organic chemistry lags far behind, although—and this is shown by the numerous recent publications—organic chemists are also aware of the fundamental importance of these processes. In this connection photochemistry plays a central role, since its instruments make it possible to carry out specific SET processes, to analyze them, and to use them i

ISSN:0570-0833    

DOI:10.1002/anie.198708251

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

摘要:

AbstractTo make sense of the marvelous electronic properties of the solid state, chemists must learn the language of solid‐state physics, of band structures. An attempt is made here to demystify that language, drawing explicit parallels to well‐known concepts in theoretical chemistry To the joint search of physicists and chemists for understanding of the bonding in extended systems, the chemist brings a great deal of intuition and some simple but powerful notions. Most important among these is the idea of a bond, and the use of frontier‐orbital arguments. How to find localized bonds among all those maximally delocalized bands? Interpretative constructs, such as the density of states, the decomposition of these densities, and crystal orbital overlap populations, allow a recovery of bonds, a finding of the frontier orbitals that control structure and reactivity in extended systems as well as discrete mole

ISSN:0570-0833    

DOI:10.1002/anie.198708461

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198708791

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198708851

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198708871

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198708881

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198708901

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198708921

出版商:Hüthig&Wepf Verlag    

年代:1987

数据来源: WILEY