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About Organic Chemistry 1.4

By Docta, Oct 30, 2011 | |
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  1. Docta
    Previously on about O C we’ve had a lightning summery of the identification of carbon as the prime element, with hydrogen, oxygen and nitrogen as components in combination for all organic substances.

    To continue we need a rudimentary understanding of quantitative analysis, as to understand how the values and mathematical formulae of organic chemistry are derived. This may not sound very exciting and trust me it’s not, but you will come away with an understanding of how big the question, “What drug is this?” or “How can I purify or test the purity of this drug?” really is.

    Structural recognition

    Just like with a library of books organic chemistry likes to catalogue every thing, these classifications are varied and at times seem unrelated but the more you learn the more you come to see that the system is almost self-evident.

    There is no single stringent method of analysis that results in discovering the structure of an unknown compound, however there is a system of experimentation and investigation that will result in being able establish physical properties and make predictions of behaviour.

    1. Physical properties (MP/BP) and purification (chromatography, crystallization, distillation, etc).
    2. Test for Halogens, Nitrogen and Sulphur. (plus Metals when dealing with salts).
    3. Measurement of Carbon, Hydrogen, Oxygen and other identifiable elements.
    4. Derive molecular formula, empirical formula, and molecular weight.

    Purification

    Any compound to be evaluated must first be isolated, it is the only way to have full conference in the results of a systematic analysis.

    As with a drug extraction a substance is obtained that has a large ratio of the compound that is to be investigated. It is this compound that is separated from the mixture.

    The most common method of purification for a solid is recrystallization.
    A suitable solvent is found where the compound is less soluble cold than hot. The substance is put into the solvent and heated, as the solvent cools the target compound precipitates as crystals and are filter out. The filtrate is washed and dried.
    The Melting point (MP)is recorded and another recrystalization is done, this cycle of taking MP and recrystallising is done until there is no deviation in the recorded MP, at this point a solid compound would be considered sufficiently isolated for analysis. (with exceptions)

    Liquids are commonly isolated by distillation taking advantage of the difference in Boiling point (BP)
    Most organic liquids can be separated by varied forms of distillation to result in a very pure compound isolated for analysis. (with exceptions)

    Chromatographic isolation

    Going down on the column….

    TO BE CONTINUED….

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