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VCL 7-3:
VCL 7-3: Qualitative Analysis - Aldehydes
In this assignment, you be given an unknown compound for which you will need to determine its chemical structure. This unknown will contain an aldehyde functional group but may also contain other functional groups as well. The tools you will have available to perform this analysis include 15 functional group tests, IR and NMR spectroscopy, plus other useful data.
1. Start Virtual ChemLab and select Qualitative Analysis S Aldehydes from the list of assignments in the electronic workbook. After entering the organic laboratory, go to the stockroom by clicking inside the Stockroom window. Next, select a round bottom flask and place it on the cork ring on the stockroom counter. On the reagent shelf you will find two or more compounds that serve as practice unknowns and another bottle that is your assigned unknown. The practice unknowns can be used to gain proficiency with the functional group tests and IR and NMR spectra interpretation. When you are ready to analyze your unknown, click on the unknown bottle and add it to the round bottom flask. Click on the green Return to Lab arrow to return to the laboratory.
2. The round bottom flask containing the unknown should now be on the cork ring on the lab bench. The boiling point and C-H analysis for the unknown are listed on the chalkboard. If the unknown is a solid, the melting point can be measured by clicking on the melting point apparatus by the reagent shelf and dragging the melting point tube to the unknown in the flask. The melting point will be displayed on the red LED, which can be enlarged by mousing over the apparatus. It will also be useful to know the polarity of the unknown by performing a TLC measurement. Record all of this information in the data table below.
Data Table C-H Analysis Melting Point (°C) Boiling Point (°C) TLC (Rf)
3. To collect an IR spectrum of your unknown, click on the IR spectrometer located underneath the laboratory clock and drag the salt plate icon to the flask on the lab bench. A window containing the IR spectrum for your product should now open. Identify the relevant peaks in the IR spectrum and record the position and associated functional group for each in the IR table below. The IR spectrum can also be saved to the lab book for later analysis.
IR List position (cm-1) & functional group 4. 1. 5. 2. 6. 3. 7.
4. To collect a 1H NMR spectrum of your unknown, click on the NMR magnet located to the right of the chalkboard and drag the NMR sample tube to the flask on the lab bench. A window containing the NMR spectrum for your unknown should now open. You can zoom into various portions of the NMR spectrum by clicking and dragging over the desired area. The Zoom Out button is used to zoom back out to view the full spectrum. Identify all of the peaks in the NMR spectrum and record the chemical shift, the splitting, and the number of hydrogens for each peak in the NMR table on the reverse side. The NMR spectrum can also be saved to the lab book for later analysis.
Chapter 7
100
Peak
Chemical Shift (δ) Multiplicity† H ‡ Peak Chemical Shift (δ) Multiplicity† H ‡
1 7
2 8
3 9
4 10
5 11
1H NMR
6 12 † Specify the multiplicity as a singlet (s), doublet (d), triplet (t), quartet (q), or multiplet (m). ‡ Specify the number of hydrogens associated with each peak.
5. To perform the functional group tests, pull down the TV by clicking on the handle located in the upper right-hand corner of the screen. Make sure the TV is in Tutorial mode. Next, click on the unknown and drag a test tube containing the unknown to the clamp over the stir plate. You should see a picture of your unknown in the TV. Now perform the bromine test by clicking on the reagent bottle labeled Br2 and drag the pipet to the test tube. The results of the test are shown in the TV with either a picture or a short video clip. Record the results of the test as either positive or negative in the table below. (See your textbook for a description of the functional group tests.) Discard the test tube by dragging it to the red disposal bucket and repeat the procedure for the other functional group tests. Make sure to record all of your results in the table below.
Results for Functional Group Tests Functional Group Test +/− Functional Group Test +/− Bromine Test Iodoform Test Permanganate Test Sodium Hydroxide Jones Oxidation Test Hydroxamate Test Lucas Test Hinsberg Test Periodic Acid Hydrochloric Acid Tollens Test Sodium Iodide/Acetone 2,4-Dinitrophenylhydrazine Sodium Iodide/Acetone + Heat Sodium Bisulfite Addition
6. Using the data you have now collected, determine the structure of your unknown compound and report the name and structure below. Be sure to include your unknown number, which is shown on the chalkboard.
Unknown # ________ Name:
Structure:
