What Is a Mechanism

Molecules can acquire extra energy by collisions, and this energy may cause distortions of bond lengths or angles by small amounts. However, the bond lengths and angles will tend to return to the equilibrium values. 

However, if the distortions become too great, one or more covalent bonds may break, and new bonds may be formed, either within the molecule or with a new molecule with which the first has collided. A chemical reaction has occurred, and when equilibrium is reached, one or more new molecules will be produced, which may be stable or may undergo further reactions. 

This chapter describes the main features of organic reaction mechanisms and how reasonable mechanisms can be written. Having worked through this chapter you should be able to  

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Considering the highly processive mechanism of the protein degradation by the proteasome, a question naturally arises what is a mechanism behind such translocation rates Let us discuss one of the possible translocation mechanisms. In [52] we assume that the proteasome has a fluctuationally driven transport mechanism and we show that such a mechanism generally results in a nonmonotonous translocation rate. Since the proteasome has a symmetric structure, three ingredients are required for fluctuationally driven translocation the anisotropy of the proteasome-protein interaction potential, thermal noise in the interaction centers, and the energy input. Under the assumption that the protein potential is asymmetric and periodic, and that the energy input is modeled with a periodic force or colored noise, one can even obtain nonmonotonous translocation rates analytically [52]. Here we... 

What is a mechanism of this reduction in strength It is an oxidative degradation of the polymer matrix of WPC, as shown in Table 6.5. 

The review of the design requirements needs to be a systematic review, not a superficial glance. Design work will commence on the basis of what is written in the requirements or the brief, although you should ensure there is a mechanism in place to change the document should it become necessary later. In fact such a mechanism should be agreed at the same time as agreement to the requirement is reached. 

The focus of Part B is on the closely interrelated topics of reactions and synthesis. In each of the first twelve chapters, we consider a group of related reactions that have been chosen for discussion primarily on the basis of their usefulness in synthesis. For each reaction we present an outline of the mechanism, its regio- and stereochemical characteristics, and information on typical reaction conditions. For the more commonly used reactions, the schemes contain several examples, which may include examples of the reaction in relatively simple molecules and in more complex structures. The goal of these chapters is to develop a fundamental base of knowledge about organic reactions in the context of synthesis. We want to be able to answer questions such as What transformation does a reaction achieve What is the mechanism of the reaction What reagents and reaction conditions are typically used What substances can catalyze the reaction How sensitive is the reaction to other functional groups and the steric environment What factors control the stereoselectivity of the reaction Under what conditions is the reaction enantioselective ... 

The ligand diethylenetriamine, H2NCH2CH2NHCH2CH2NH2, forms stable complexes with Pt2+. When the complexes [Pt(dien)X]+ undergo reaction with pyridine, the rate constants for X = Cl-, I-, and N02- are 3.5 X 10-5, 1.0 X 10-s,and5.0 X 10-8 sec-1, respectively. What is the mechanism forthe substitution reactions Provide an explanation for the difference in rates of the reactions. What would be a reasonable estimate for the rate constant when X = Br- Explain your answer. 

Records describe what has been done and the outcome of the activity. It is important that records are kept safely and that unrecorded changes are not made. Therefore, records have to be controlled in much the same way as documents. It is important that records are clearly identified, accessible and retained for as long as the customer requires. This can be up to 30 years but could be much shorter. The archiving of records can be in any format. However, it is important that they do not deteriorate and that there is a mechanism for reading them if they are in electronic format. 

A patient with AIDS is treated with a combination of agents, which includes zidovudine. What is the mechanism of action of zidovudine ... 

A 45-year-old female has a bone marrow transplant for treatment of ovarian cancer Cyclosporine is given as an immunosuppressant What is the mechanism of action of cyclosporine ... 

A 47-year-old female comes to the emergency department (ED) with severe crushing chest pain of one hour s duration Electrocardiogram and blood chemistries are consistent with a diagnosis of acute ME Streptokinase is chosen as part of the therapeutic regimen. What is its mechanism of action ... 

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