Qualitative organic analysis basis

Qualitative organic analysis, 1027 see also End papers basis of, 1027 ... 

A successful systematic scheme of qualitative analysis for identifying organic compounds was developed early in the twentieth century. This scheme, together with some more recent modifications, is termed classic qualitative organic analysis, and it is the basis for most textbook discussions on the subject (Ref. 1 at the end of Section 25.5, for example). 

Although the Hiickel method has now been supplanted by more complete treatments for theoretical analysis of organic reactions, the pictures of the n orbitals of both linear and cyclic conjugated polyene systems that it provides are correct as to symmetry and the relative energy of the orbitals. In many reactions where the n system is the primary site of reactivity, these orbitals correctly describe the behavior of the systems. For that reason, the reader should develop a familiarity with the qualitative description of the n orbitals of typical linear polyenes and conjugated cyclic hydrocarbons. These orbitals will be the basis for further discussion in Chapters 9 and 11. 

A primary goal of this chapter is to learn how to achieve control over the pH of solutions of acids, bases, and their salts. The control of pH is crucial for the ability of organisms—including ourselves—to survive, because even minor drifts from the optimum value of the pH can cause enzymes to change their shape and cease to function. The information in this chapter is used in industry to control the pH of reaction mixtures and to purify water. In agriculture it is used to maintain the soil at an optimal pH. In the laboratory it is used to interpret the change in pH of a solution during a titration, one of the most common quantitative analytical technique. It also helps us appreciate the basis of qualitative analysis, the identification of the substances and ions present in a sample. 

A plot of this sort is useful for qualitative analysis, especially of outliers. A study of the test conditions (e.g., the activating systems used) the particular strain of test organisms (e.g., its sensitivity to frame shifts vs. base substitutions), or the chemical nature of the mutagen may reveal the basis for the discrepancy and ultimately yield deeper insights. For example, the discrepancy in the two tests for furylfuramide (the extreme outlier in Figure 9-2) could be due to different nitroreductase activities in the two systems, which would lead to differences in capacity to convert the chemical into an active form. 

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