16 Jul 2012

Simple synthesis of MoO2(acac)2 and evaluation of spectra

Lab Experiment

Submitted by Patricia L. Stan, Taylor University
Categories
Description: 

A very simple lab synthesis that allows the student to carry out a coordination reaction and then look at the NMR and IR spectra.  I use this as a first lab to introduce them to using the NMR and IR.  If students work through the spectroscopy tutorial they should be able to explain the IR and NMR spectra.

Learning Goals: 

A student should be able to explain simple NMR splitting patterns.

A student will use spectroscopy to show they have synthesized a desired compound.

Students will work through a spectroscopy tutorial http://www.chem.ualberta.ca/~inorglab/spectut/TblofCont.html

 

Equipment needs: 

Vial with stir vane, stir plate, IR, NMR

Implementation Notes: 

I developed the lab from the paper by Arnaiz and have tried to get my students to use the spectroscopy tutorial.  By asking them to do some analysis of spectra in the lab I hope to encourage the students to actually work through the tutorial.  I need to add more NMR questions to the lab to make sure they work in depth on the tutorial.

Using a stir vane in the conical vial works well instead of using a stirring rod.

Time Required: 
1 hour for synthesis + time to show students instruments
Evaluation
Evaluation Methods: 

Have not tried the lab website combination yet but have tried each separately with some success.

Evaluation Results: 

A class of 6 students were all able to complete the synthesis with good yield.   Students had to stir longer than indicated in the paper 10 minutes instead of 1 minute.  The NMR was not great as it had limited solubility in the dueterated chloroform we had available.  I have ordered the CD2CL2 suggested in the paper, hopefully this will solve the problem.  IR seemed to be fine.

Students were within 1-10 degrees of the reported melting point of 179C. Good yields, 50-80% of resonably pure yellow product were obtained. The IR spectrum of  the compound should show two strong bands at 900 and 930 cm-1 corresponding  to  the stretching vibrations characteristic of the cis MoO2.  Singlets at 2.12  and 2.14  ppm (CD2Cl2, room temperature) should be seen, assignable to  the two sets of inequivalent methyl groups in the 1H  NMR  spectrum.

 

Creative Commons License: 
Creative Commons Licence

Comments

This is an introductory exercise and gives time in the lab for the students to learn to use NMR and IR and take a spectrum. My thought is that they could then use the tutorial to discuss their results and maybe students could take a spectrum of the starting material as well to compare with the results.

Students have plenty of time to isolate product and learn to use the NMR and IR.  I want my students who are new to NMR and IR to interpret what they get and maybe compare to spectra of the starting material.

Patricia, I'm flattered to see that you are having your students use an online tutorial that I developed along with some dedicated undergraduates.  I'd be interested in hearing how they find it, especially whether the acac examples on NMRpg17 and NMRpg18 are useful in the context of understanding the results of the experiment you mentioned (which I'll be looking into adding into my own curriculum precisely for the reasons you mentioned in your discussion).  Cheers, Jason

Tricia,  I used this lab this past semester and it worked great!  I expanded the introduction a bit and I will share it with others in the near future.  I also created a CIF file containing the crystal structure of the compound and had students try to calculate the which Mo-O vibrations lead to the observed peaks in the IR spectrum.  This was not so successful, however.  I think I was having an issue with the input file.

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