QUALITATIVE IDENTIFICATION OF ORGANIC COMPOUNDS

Not only are physical properties used to characterize a specific organic compound, buf they are often used to compare one compound to another. Examples of fhis approach are illustrated in Chapter 9, Qualitative Identification of Organic Compounds. The route to identification of an unknown organic species has become increasingly dependent on the measurement of the physical properties of the pure substance. 

See, for example, the following laboratory texts (a) Sorum, C. H. Lagowski, J. J. Introduction to Semimicro Qualitative Analysis, 5th ed. Prentice-Hall Englewood Cliffs, NJ, 1977. (b) Shriner, R. L. Fuson, R. C. Curtin, D. Y. The Systematic Identification of Organic Compounds, 5th ed. John Wiley and Sons New York, 1964. 

N. D. Cheronia J- B. Entrikin and E W. Hodnett, Semimicro Qualitative Organic Analysis The Systematic Identification of Organic Compounds. 3rd edition, Krieger, Melbourne (1983). 

We use the term qualitative organic analysis for the identification of organic compounds as well as for that of some atoms or of some groups of atoms present in an organic molecule. Both identifications are actually located in two different fields of organic analysis ... 

The basic aims of organic qualitative analysis are the detection and the identification of organic compounds. As other terms for both ideas some-times appear in the literature, we shall first give their definitions. 

WATER-AIR EQUILIBRATION. McAuliffe (6) introduced a multiple phase equilibrium procedure for the qualitative separation of hydrocarbons from water-soluble organic compounds. For n-alkanes, more than 99% were found to partition in the gas phase after two equilibrations with equal volumes of gas and aqueous solution. Cycloalkanes require three equilibrations to be essentially completely removed, and oxygen-containing organic compounds (e.g., alcohols, aldehydes, ketones, and acids) remain in the aqueous layer. Thus, after equilibration with equal volumes of gas, an immediate clue is given regarding the identification of the compound. More details of this technique can be found in Chapter 7. 

The introduction of GC as an analytical technique has had a profound impact on both qualitative and quantitative analysis of organic compounds. Identification of compounds by GC can be accomplished by their retention times on the column as compared to known reference standards, by inference from sample treatment prior to chromatography, " or by the concept of retention index. " The latter method and tables of retention indices " with associated conditions have been reported. " Although qualitative data and analytical techniques for identification of compounds are well-established " and relative retention data for over 600 substances also have been published, " the main utility of GC undoubtedly lies in its powerful combination of separation and quantitative capabilities. Use in quantitative analysis involves the implementation of two techniques being performed concurrently, i.e., separation of components and subsequent quantitative measurement. 

In general, the reactions of organic compounds at a voltammetric electrode are slower and more complex than those for inorganic species. Consequently, theoretical intei-pretation of the data is often more difficult or impossible. Generally, a much stricter adherence to detail is required for quantitative work. Despite these handicaps, organic polarography has proved fruitful for the determination of structure, the quantitative analysis of mixtures, and occasionally the qualitative identification of compounds. 

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