Ir spectroscopy lab report

CHEM 2243 Introduction to Infrared Spectroscopy and Qualitative Tests Purpose: In this virtual lab experiment, you will explore the use of infrared spectroscopy and various qualitative tests to distinguish between four organic compounds: acetophenone, benzaldehyde, benzoic acid, and benzyl alcohol. Infrared spectroscopy is useful for distinguishing classes of organic compounds (ie. functional groups). We can identify functional groups using infrared (IR) spectroscopy. IR radiation is in the same range of frequencies (4000-600 cm-1) as the stretching and bending vibrations of bonds in organic molecules. When the frequency of the radiation exactly matches the frequency of the bond, the molecule absorbs energy, resulting in an absorption peak in the IR spectrum. Most Page 1 of 8 functional groups show absorption bands in the region of 4000-1400 cm-1. See the handouts: Characteristic Infrared Absorption Peaks and IR Tutorial UCLA for help identifying the peaks. Prior to modern spectroscopy and spectrometry techniques, one way that chemists used to identify classes of organic compounds was through qualitative tests. These simple chemical tests can be used to indicate the presence (or absence) of certain functional groups. You will use the Beyond Labz virtual platform to record the IR spectra, and to perform the following qualitative tests on the four organic molecules that you are investigating in this virtual lab experiment. (acetophenone, benzaldehyde, benzoic acid, and benzyl alcohol). Functional group qualitative tests: Permanganate Test: A purple permanganate solution is placed in a test tube and unknowns are added directly to the permanganate solution. For solid unknowns, the solid is first dissolved in acetone. If the purple color of the permanganate persists, the test is negative. If the solution changes from purple to brown (MnO2), the molecule is oxidizable and the test is positive and the unknown contains one or more of the following: alkene, primary or secondary alcohol, or an aldehyde. Jones Test: The unknown is mixed with acetone to produce a saturated solution, and then added to the Jones reagent (chromic acid). The persistence of the bright orange color indicates a negative test. A color change to blue or green is a positive test. A rapid change to a light blue color indicates a primary or secondary alcohol. If the color change takes longer than one or two seconds, the unknown contains an aldehyde. Tollens Test: Concentrated aqueous NH3, 5% aqueous AgNO3, and 10% aqueous NaOH are added to a test tube followed by a minimal amount of the unknown. The formation of a silver mirror on the test tube wall is a positive test for aldehydes and reducing sugars. 2,4-Dinitrophenylhydrazine Test (DNPH): Liquid unknown or a solution containing the solid unknown and ethanol is added to the orange dinitrophenylhydrazine solution. The formation of a precipitate ranging in color from red to yellow is a positive test for aldehydes and ketones. Allylic and benzylic alcohols may also give a positive test. Absence of a precipitate is a negative test. Iodoform Test: The unknown and a small amount of 10% aqueous NaOH are heated to 60˚C. KI/I2 is then added to the solution followed by the addition of NaOH until the solution is again colorless. The appearance of a light-yellow precipitate is a positive test for methyl ketones. Alcohols which may be oxidized to produce methyl ketones or acetaldehyde may also give positive tests. If the solution remains clear, the test is negative. Page 2 of 8 Virtual Lab Instructions (video instructions also available). Help is available by clicking on the bell on the stockroom counter. 1. Open the organic chemistry lab on the Beyond Labz platform. Select “Qualitative Analysis” at the top left of the screen to open the Qualitative Analysis virtual lab. *Note: The order that you test the four compounds in the virtual lab does not matter. Likewise, the order that you perform the qualitative tests also does not matter. The instructions are simply written in the order that the compounds appear by functional group on the chalkboard, and then by the order that the reagents appear on the benchtop. What matters is that for each compound you record the IR spectrum and the results (+ or -) of each test. **Note 2: Although you will be practicing recording the IR spectra in the virtual lab, you are provided with the spectra at the end of this handout with the key peaks clearly labeled. 2. Select “Alcohols” from the chalkboard, then click and drag (or double-click) the reagent bottle for the benzyl alcohol to add it to the flask.