ISSN:0570-0833    

DOI:10.1002/anie.198602973

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY

摘要:

Abstract“Die Ringschließung ist offenbar diejenige Erscheinung, welche am meisten über die räumliche Anordnung der Atome Auskunft geben kann. Wenn eine Kette von 5 und 6 Gliedern sich leicht, eine von weniger oder mehr Gliedern sich schwierig oder auch gar nicht schließen läßt, so müssen dafür offenbar räumliche Gründe vorhanden sein.… Die vier Valenzen des Kohlenstoffatoms wirken in den Richtungen, welche den Mittelpunkt der Kugel mit den Tetraederecken verbinden, und welche miteinander einen Winkel von 109°28′ machen. Die Richtung der Anziehung kann eine Ablenkung erfahren, die jedoch eine mit der Größe der Letzteren wachsende Spannung zur Folge hat,”[Ring formation is evidently the reaction that can provide the most important information on the spatial arrangement of atoms. Steric reasons should explain the observation that 5‐ or 6‐membered chain undergoes ready closure, whereas a shorter or longer chain undergoes difficult or no closure.… The four valences of the carbon atom act in the directions that connect the center of a sphere with the corners of a tetrahedron and form angles of 109°28′ with one another. The direction of the attraction can deviate, but this in increasing strain as the sizes of the latter increase.] This is the quintessence of the “ring‐strain theory” formulated byAdolf von Baeyerover one hundred years ago. Although it is today only one facet of the many aspects of strain theory, it has repeatedly stimulated experimental and theoretical chemists. Among the most spectacular of the recent successes in synthetic chemistry are the syntheses of tetra‐tert‐butyltetrahedrane and [1.1.1]propellane. The reasons for the great stability of these two highly strained compounds are completely different. The experimental findings as well as the results of theoretical analysis by means of molecular mechanics and ab initio calculations have contributed decisively to our present state of knowledge of the structure, ener

ISSN:0570-0833    

DOI:10.1002/anie.198603121

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY

摘要:

AbstractEXAFS measurements indicate the presence of a quasi lattice‐like ordering of simple ions in dilute solutions. Small‐angle X‐ray scattering (SAXS) measurements on dilute aqueous solutions of synthetic macroions, polynucleotides, and proteins show a single broad peak; a binary mixture of synthetic macroions of different molecular weight gives a new scattering curve that is entirely different from the composite curve of the constituents before mixing. This would indicate that the macroions are distributed in a fairly regular way in the solution. The intermacroion spacing (2Dexp) obtained by the Bragg equation is found to be smaller than the average spacing (2D0) calculated from the polymer concentration. Furthermore, the 2Dexpvalue decreases with increasing number of charges per macroion. This finding is confirmed by studies on model systems, e. g. on monodisperse ionic latex particles, which are large enough (diameter: about 3000 Å) to be seen under the ultramicroscope. It follows, from the inequality relation 2Dexp<2D0, that there is an attraction between ionic species of like‐charge. This conclusion contradicts prevailing views in colloid chemistry; it has been pointed out that such a behavior can be explained in terms of a new theory, in which counterions between the macroions or ionic latex particles play a decis

ISSN:0570-0833    

DOI:10.1002/anie.198603231

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198603351

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198603361

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198603381

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198603391

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198603401

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198603421

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198603441

出版商:Hüthig&Wepf Verlag    

年代:1986

数据来源: WILEY