Posted: September 16th, 2017

Lab 24 Guide VCL 10-1: Grignard Addition – 1

Lab 24 Guide
VCL 10-1: Grignard Addition – 1

For this assignment, the target compound that you should synthesize is 1-phenyl-1-propanol. This is an organometallic addition reaction. Examine the product and identify potential bonds that may be formed. Keep in mind the mechanism and the need to quench the reaction with acid to liberate the neutral product.

Synthesis Procedures
1.    Start Virtual ChemLab and select Grignard Addition –1 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. Using the available reagents on the stockroom shelf, identify the appropriate starting
materials required to synthesize the target compound and add them to the round bottom flask. Select the appropriate solvent and click on the green Return to Lab arrow to return to the laboratory.

2.    The round bottom flask containing the starting materials should now be on the stir plate. Click on the handle located in the upper right corner of the laboratory to pull down the TV. The TV should already be in Tutorial mode and the starting materials and solvent should be listed. From the group of reagents found on the lab bench, select the correct reagent to synthesize the target compound and add it to the flask on the stir plate.

3.    Start the reaction by clicking on the Stir button on the front of the stir plate. You should be able to observe the reaction mixture stirring in the flask. Monitor the progress of the reaction using TLC measurements as necessary until the product has formed and the starting materials have been consumed. You can advance the laboratory time using the clock on the wall. With the electronic lab book open (click on the lab book on the lab bench), you can also save your TLC plates by clicking Save on the TLC window.

4.    When the reaction is complete, “work up” your reaction by first dragging and dropping the separatory funnel (located in a drawer) on the flask and then adding H2O to the funnel. Extract the organic layer in the funnel by clicking on the top layer and dragging it to the cork ring on the lab bench. Your target compound should now be in this flask.

List the starting materials, solvent, reagent, and products formed: ethyl-MgBr, benzaldyhyde,

ether, 1-phenyl-1-propanol

How long did it take to finish the reaction? 30 minutes

What are the TLC values (Rf) for (a) Starting Materials: 0.55    (b) Products: 0.45

Write a mechanism for this reaction:

6.    To collect a 1H NMR spectrum of your product, 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 product 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 below. The NMR spectrum can also be saved to the lab book for later analysis.

1H NMR

Structure:

OH

1-Phenyl-1- propanol
Peak    Chemical Shift (d)
Multiplicity†
H‡
Peak    Chemical Shift (d)
Multiplicity†
H‡

† 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.

Do the IR and NMR spectra you measured and recorded in the tables above confirm that you synthesized the assigned target compound? Explain.