4 Apr 2011

19F NMR In-class exercise

In-Class Activity

Submitted by Sheila Smith, University of Michigan- Dearborn
Categories
Description: 

This is an in class activity to introduce the topic of multinuclear NMR, which is not covered (beyond 13C) in our sophomore level organic course. It is designed to walk the students through the process of predicting NMR spectra, as they learned in sophomore organic chemistry, but for a different I=1/2 nucleus, in this case 19F, which is I=1/2 and 100% abundant. 

 

AttachmentSize
PDF icon FNMR_ Inclassexercise_worksheet.pdf27.25 KB
Learning Goals: 

The student will be able to predict the molecular structure of an inorganic fluorinated compound. The student will be able to use basic symmetry arguments to identify equivalent nuclei. The student will be able to draw a stick diagram to predict the splitting pattern (including relative intensities) of an NMR peak. The student will be able to predict the integrations for various peaks in an NMR spectrum. The student will be able to use basic shielding arguments to order the peaks in a predicted NMR spectrum according to chemical shift. The student will be able to sketch a predicted 19F NMR spectrum.

 

Equipment needs: 
No instrumentation is required. Instructors may choose to provide quadrille paper for stick diagrams.
Related activities: 
Implementation Notes: 

I found it helpful to walk through the procedure for predicting 1H NMR spectra using a simple molecule like ethylbenzene, before asking my students to do the same for this fluorine compound.

 

Time Required: 
Depending on the preparedness of your students, this exercise may take anywhere from 15 minutes to an entire class period.
Evaluation
Evaluation Methods: 
The usefulness of this in class exercise can be assessed based on the quality of the discussion that it produces, both in terms of review material (VSEPR, 1H NMR spectra prediction) and in increasing student understanding of new material. It can also be evaluated through inclusion of similar problems on homework sets and exams.
Evaluation Results: 
I was somewhat surprised by how few of my junior level students were even aware that NMR could be run on nuclei other than protons and carbon. Most had forgotten the stick diagrams, (but remembered, for example, that splitting by 2 nuclei would give a triplet... many students predicted that a quartet would have a 1:2:2:1 pattern.
Creative Commons License: 
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