Lewis acid catalysts, eg. Fe3+, Ru3+, Zn2+, etc., for certain organic Thesis Proposal

Lewis acid catalysts, eg. Fe3+, Ru3+, Zn2+, etc., for certain organic transformations - Thesis Proposal Example te possesses a series of basic sites, reaction specificity is necessary for that particular interaction between acid and base so that the desired functionality is achieved and not the other. The Lewis acid predetermines the nature of the intermediate cationic specie. It can be an ion pair, a covalent compound with weak C-X bond or an intermediary compound (Suzuki 1557). Lewis acids found their applications in a range of carbon-carbon forming reactions. Usually, Mukaiyama aldol synthesis (Mukaiyama, Banno, and Narasaka 7503), Diels-Alder reactions (Clayden, Greeves, Warren, and Wothers 905) ene reactions and Friedel-Crafts reaction (Clayden, Greeves, Warren, and Wothers 920) are catalysed by commonly employed Lewis acids such as BF3, TiCl4, SnCl4 and AlCl3. These compounds can activate a series of organic groups and usually exist as dimers, trimmers or oligomers. In most cases, such reactions are highly efficient but with little or no chemo, region or stereoselectivity. It was noted that only small changes in ligands, surrounding the central metal ion can lead to monomeric structures in organic solvents thus increasing their acidity and reactivity. Also, these changes in ligands change the way the newly formed Lewis acids interact with their substrates, thus manifesting new selectivity (Yamamoto and Saito 239). As an example of the idea presented above, two compounds can be put forward: MAD (bis(2,6-di-tert-butyl-4methylphenoxide) methylaluminum) and ATPH (tris(2,6-diphenylphenoxide) tris(2,6-diphenylphenoxide)). Both compounds were prepared from Me3Al and the corresponding, highly substituted phenol according to the scheme below: Both compounds are highly useful in highly specific chemical transformation. It is possible to lower the activity of the Lewis acids prepared in a way that ATPH was by taking more electron donating organic substrates. Comparing to conventionally employed Lewis acids, it was established that the steric effect of the presented above

Evaluation of structure and composition of early childhood narrative Essay

Evaluation of structure and composition of early childhood narrative - Essay Example 3 "Chinese children, generally speaking, include more narrative components,evaluative information, and temporal markers in their narratives over time.However, the growth patterns and rates of change for each child on eachnarrative measure vary (Chang,Chein Ju 2004,page 83-104)". All of these three criteria (narrative structure, evaluation, and temporality) are kept in mind when analysing the stories I have collected from children in the appropriate age range. This essay will employ the Labovian six part narrative model and Hoey's concept of problem-solution pattern to assess the texts. Appendix (1) shows examples of the concepts that will be employed and tested against the children's narrative. Not all of these elements are present in every story, but a majority of the Labovian model fits the narratives. Appendix (1): Labov's and Hoey's Approaches These two concepts will be used to test the data below. Fig. 1: Labov's six part model (Labov. William, Waletzky.J 1967) ABSTRACT- What happened in the beginning ORIENTATION- Who, where and when COMPLICATING ACTION- What happened EVALUATION- The high point RESOLUTION- What finally happened CODA- Final summary which brings listener and speaker back to the present time Fig. 2: Hoey's concept of predictable patterns Situation (optional) Problem Response OR Negative Evaluation Positive Evaluation and Or Result Or Result Hypothesis My hypothesis is that as a child is introduced to... This study builds on many other works as the Labovian model is now frequently used to assess children's narratives, (Kernan, 1977; Eaton, Collis and Lewis, 1999). The idea of linguistic and narrative development in children is also a popular issue. One study that specifically charts the evolution of child narrative with age is Telling stories of experiences: Narrative development of young Chinese children a study by Chien-JuChang in which young Chinese children were visited in their homes at age three years and six months and then at three month intervals for the next nine months. This essay will employ the Labovian six part narrative model and Hoey's concept of problem-solution pattern to assess the texts. Appendix (1) shows examples of the concepts that will be employed and tested against the children's narrative. Not all of these elements are present in every story, but a majority of the Labovian model fits the narratives. My hypothesis is that as a child is introduced to more narrative texts, and comes to identify narrative components, that he or she will