Plan Strain Model

Basis for the planned investigation are the creep curves of plastics under the influence of media. To describe the material behaviour of the plastics in the creep test the material models of Kelvin-Voigt and Maxwell are used. The combination of these two models can be seen in Figure 9. They are formed by a parallel and a serial use of a spring and a damper. According to this model the strain can be described as a function of the constant stress gq and the properties of the springs and dampers as follows ... 

In the projected synthesis of vitamin B12, the plan called for the construction of a key intermediate by the stereospecific cyclization of a stereochemically well-defined 1,3,5-triene to the corresponding 1,3-cyclohexadiene. From the inspection of molecular models, Woodward and his colleagues were confident that the minimization of angle strain coupled with appropriate orbital overlap would favor a conrotatory cyclization. While the reaction was indeed found to be highly stereospecific, it took the disrotatory path instead. To explain the observed contradiction, it was necessary to recognize a new control element that Woodward and Hoffmann christened conservation of orbital symmetry [2, 3]. 

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