Organic structure determination reasoning process

The final section, on analytical chemistry, is a combination of structure-elucidation techniques and instrumental optimizations. Instrumental analysis can be broken into several steps method development, instrumental optimization, data collection, and data analysis. The trend today in analytical instrumentation is computerization. Data collection and analysis are the main reasons for this. The chapters in this section cover all aspects of the process except data collection. Organic structure elucidation is really an extension of data analysis. These packages use spectroscopic data to determine what structural fragments are present and then try to determine... 

Macro- as well as microfractionation techniques need to be developed, as necessary steps in attaining the goal of organic structure elucidation. Now that several hundred grams of aquatic humic substances can be isolated from water at reasonable time and cost, it is not unrealistic to plan to process this quantity of material to obtain milligram quantities of pure substances for structural studies. Once some structures have been determined, it should be possible to miniaturize the fractionations and use mass spectroscopy for structure identification. 

Cells and groups of cells in developing organisms become progressively committed to form specific structures. This remarkable process is known as determination (1). In spite of its importance — E. B. Wilson (2) called it "the fundamental problem...which includes all others" — determination has received far less attention from molecular biologists than has cell differentiation. One reason may be that determination is not a visible property of cells. It is only discernible when the normal process of development is experimentally manipulated. 

At one time, the structures of organic compounds were deduced by chemical reactions that related a compound of unknown strucmre to compounds whose structures were known. Many chemical reactions had to be carried out to accomphsh this task. It was possible to reason backward to postulate what the structure of the original compound must have been to yield the observed products. Structure determination by chemical reactions is a time-consuming process. For example, if we want to determine the structure of a relatively simple compound with molecular formula, we will find that 88 isomers are possible, including ethers, alcohols, aldehydes, and ketones. Many chemical reactions would be required to identify the functional group and to determine the hydrocarbon skeleton. Structure determination by chemical reactions also has another severe limitation each reaction destroys part of the sample of the unknown compound. Spectroscopic structure determination requires only small amounts of a compound, and the experimental methods require very litde time compared to the arduous process of determining a molecular structure by a series of chemical reactions. 

The structures of all the aminoacyl-tRNA synthetases of E. coli have been determined. Researchers have divided them into two classes (Table 27-7) based on substantial differences in primary and tertiary structure and in reaction mechanism (Fig. 27-14) these two classes are the same in all organisms. There is no evidence for a common ancestor, and the biological, chemical, or evolutionary reasons for two enzyme classes for essentially identical processes remain obscure. 

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