lab 7 - Experiment VII. Identification of an unknown...

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Experiment VII. Identification of an unknown organic compound from physical properties, chemical reactivity and infrared spectroscopy. Review the relevant mechanisms in any introductory organic chemistry textbook. See, for example, KPC Vollhardt and NE Schore, Organic Chemistry . Introduction Structure elucidation or identification of chemical compounds is one of the more challenging tasks a chemist will face. Many branches of chemical science are involved in identification of substances. Some examples are: a) Characterization of reaction products. b) Screening of new drug candidates from natural sources, i.e.; plants, animals, fungi or microorganisms. c) Analysis of deadly toxins in medicinal chemistry and forensic medicine. The steps in involved in structure elucidation or identification of an unknown compound make the process a logical puzzle. In order to solve this problem, it requires some problem solving skills, planing and preparation. The unknown you will be provided with is among the compounds listed in tables at the end of the manual. Some of these compounds are quite hazardous so use proper precautions. You are required to perform a variety of chemical experiments to establish the identity of the unknown. Experiment VII will require you to use your own initiative and work individually. You are therefore allowed to use this lab handout during the lab period and you don’t need to copy the procedures to your lab notebook . Your prelab should include a flowchart that will describe the possible routes for identifying the unknown. You are encouraged to perform enough tests to positively identify your unknown. There is of course a minimum amount of data required. The identification process begins with classification of the compound based on its functional groups. The presence of a particular functional group can be deduced from solubility tests and an IR spectrum. In addition, specific chemical reactions (“chemical tests”) are used to reveal the presence of certain functional groups. The chemical tests are characterized by a visual change that indicates if a reaction took place. Common visual outcomes are color change, formation of precipitate or formation of bubbles. For example, for identifying an alcohol, we can react the unknown with chromic acid. If an oxidation reaction of the alcohol will occur, the color of the solution will change from orange to green. Therefore the change of color indicates that the unknown may be an oxidaizable alcohol. 1 Once the functional group is indentified, the specific identity of the compound can be achieved by comparing the melting point or boiling point of the unknown to literature values of known compounds. Several tables of possible unknowns are provided at the end of this manual. To further confirm the identity of the compound, a sample of the unknown is reacted with specific reagents to give a new compound (“derivative”). The derivatives are compounds that can be purified easily and have a
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lab 7 - Experiment VII. Identification of an unknown...

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