Entropic factors

Adsorption of macromolecules has been widely investigated both theoretically [9—12] and experimentally [13 -17]. In this paper our purpose was to analyze the probable structures of polymeric stationary phases, so we shall not go into complicated mathematical models but instead consider the main features of the phenomenon. The current state of the art was comprehensively summarized by Fleer and Lyklema [18]. According to them, the reversible adsorption of macromolecules and the structure of adsorbed layers is governed by a subtle balance between energetic and entropic factors. For neutral polymers, the simplest situation, already four contributor factors must be distinguished ... 

The linking of two weaker binding compounds may lead to strong binding one, primarily due to the saving of one entropical factor if both original compounds are chemically connected ... 

Entropic Factors Should be Related to Well-Defined Potential Surfaces... 

In order to explore the significance of entropic factors, we must relate the different hypotheses to the clear concept of potential surfaces. Thus we start... 

Entropic Factors in Model Compounds and Their Relevance to Enzyme Catalysis... 

In view of the arguments presented in this chapter, as well as in previous chapters, it seems that electrostatic effects are the most important factors in enzyme catalysis. Entropic factors might also be important in some cases but cannot contribute to the increase of kcJKM. Furthermore, as much as the correlation between structure and catalysis is concerned, it seems that the complimentarity between the electrostatic potential of the enzyme and the change in charges during the reaction will remain the best correlator. Finally, even in cases where the source of the catalytic activity of a given enzyme is hard to elucidate, it is expected that the methods presented in this book will provide the crucial ability to examine different hypothesis in a reliable way. 

S is the entropic factor, which depends on Eb and the chemical substance structure ... 

These unsatisfactory (easily replicated) results have led to a search for other approaches to the calculation of the entropic factor. 

This reasoning is based on faith in experimental data. This is justified by the values resulting from j rule 7, which give a remarkable consistency in the entropic factor calculated by using equation 2 (respectively 6.392 6.347 and 6.334 at 20. 30 and 50°C). These results show that S > So is most often verified in the series considered, as shown in the ... 

The Hass table of group attribution of the entropic factor is first considered ... 

II and II, are estimated degrees only there is no experimental value involved except for AIT and calculation of the entropic factor from equation (1) by Hass. The process is indicated in the chart below ... 

The enthalpy of formation of the substance that is obtained is for the gaseous state. The enthalpy that corresponds to the gas -> liquid change of state therefore needs to be added. The enthalpy corresponding to the liquid solid change is to be ignored if the enthalpy of formation of a substance in the solid state is required, since there is not much difference between the two. For the enthalpy of formation in the liquid state the enthalpy of condensation is calculated from the equation that bonds it to the entropic factor discussed in Chapter 1, ie ... 

The reactivity order of alkenes is that expected for attack by an electrophilic reagent. Reactivity increases with the number of alkyl substituents.163 Terminal alkenes are relatively inert. The reaction has a low AHl and relative reactivity is dominated by entropic factors.164 Steric effects govern the direction of approach of the oxygen, so the hydroperoxy group is usually introduced on the less hindered face of the double bond. A key mechanistic issue in singlet oxygen oxidations is whether it is a concerted process or involves an intermediate formulated as a pcrcpoxide. Most of the available evidence points to the perepoxide mechanism.165... 

Hydroamination involves the addition of primary or secondary amines to alkenes to afford terminal or branched higher value substituted amines via anti-Markovnikoff or Markovnikoff addition.144 Although the addition of RNH2 to C=C is thermodynamically favorable (Equation (14)), there is a strong entropic factor disfavoring N-H addition which has to be overcome through use of a metal catalyst. 

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