Historical retrospect

This chapter begins with a short historic retrospect about the development of the carbocation concepts and covers the techniques used for their generation, observation, and characterization under superacidic long-lived conditions. This is followed by an extensive coverage of the multitude of trivalent (classical) and equilibrating (degenerate) and higher (five or six) coordinate (nonclassical) carbocations. 

Cf. S. T. Possony, The Ukrainian-Jewish Problem Historical Retrospective , Ukrainian Quarterly 2 (1975), pp. 141ff. 

Schmidt W, Weber OF. In memoriam of Rudolf Virchow a historical retrospective including aspects of inflammation, infection, and neoplasia. Contrib Microbiol. 2006 13 1-15. 

In 2009, Yu and co-workers wrote a comprehensive review on diastereo-selective and enantioselective C—H bond functionalization by transition metal catalysts, which presented the historical retrospective of this area in an elegant manner. Therefore, in the following sections, we will focus on the discussion of the latest achievements on the catalytic asymmetric C—H bond functionalization via a transient C—M bond (mainly contributions after 2009). The reactions will be classified according to the metal catalyst as well as the mechanistic scenario. Note that asymmetric hydroacylation and hydrovinylation, two important kinds of methods for the functionalization of aldehyde and alkene C—H bonds, will be covered in two separate chapters of this book (Chapters 8 and 9). 

Our review starts with the general formulation of the GGS model in Sect. 2. In the framework of the GGS approach many dynamical quantities of experimental relevance can be expressed through analytical equations. Because of this, in Sect. 3 we outline the derivation of such expressions for the dynamical shear modulus and the viscosity, for the relaxation modulus, for the dielectric susceptibility, and for the displacement of monomers under external forces. Section 4 provides a historical retrospective of the classical Rouse model, while emphasizing its successes and limitations. The next three sections are devoted to the dynamical properties of several classes of polymer networks, ranging from regular and fractal networks to network models which take into account structural heterogeneities encountered in real systems. Sections 8 and 9 discuss dendrimers, dendritic polymers, and hyperbranched polymers. 

After the above historical retrospective devoted to linear Rouse chains, we follow the extension of this approach to polymer systems that have more complex topologies. We focus first on the dynamics of networks cross-Unked from... 

This historical retrospect refers to three important traditions. (1) The Exodus out of Egypt (2) The inimical threat during the journey through the desert, and (3) The conquest of the Holy Land. This plea apparently evoked a consciousness among the people of Israel that they had failed. They seek to appease the divine with excessive and almost impossible gifts thousands of rams and even the fife of the firstborn child. This merchandising proposal, however, is coimtered with an instruction that is much more human and humane ... 

Gordon, 1943. Neil E. Gordon. The Section, Division, and Journal of Chemical Education A Brief Historical Retrospect . Journal of Chemical Education 20 369-372, 405. 

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