27 Jun 2016

Determination of the O-H stretching frequency by isotopic substitution using IR spectroscopy

Lab Experiment

Submitted by Kari Stone, Benedictine University
Categories
Description: 

This experiment explores isotopic substitution as a method to identify stretching frequencies and linking experimentally determined parameters with theoretical predictions utilizing a simple harmonic oscillator obeying Hooke’s law.

AttachmentSize
File Student Handout30.26 KB
File Instructions for Formal Report65.46 KB
Learning Goals: 

Students will use IR spectroscopy and isotopic substituion in order to predict theoretical frequency shifts in IR spectra of an O-H bond.

Students will synthesize their results into an organized and coherent lab report as described in the student instructions.

Equipment needs: 

FT-IR

Salt plates

CH3OH and CH3OD

Implementation Notes: 

If you are using this in a sophomore level class, it will be important to spend time discussing organic functional groups and where they show up in the IR spectra. I also spend time discussing correlations between bond strengths and bond lengths and how these are related to IR stretching frequencies. Importantly, any isotopically substituted molecule would work so that an analysis of different types of organic functional groups would enhance this lab.

Time Required: 
3 hours
Evaluation
Evaluation Methods: 

Students should be able to generate a formal lab report and detail methods of isotopic substitution for frequency determination. They will showcase their experimental data and compare to their theoretical prediction. They will need to be very clear about how they calculated their theoretical frequency.

Creative Commons License: 
Creative Commons Licence

Comments

I was looking for something new and I came across this lab. It fits in really well with material I cover in my sophomore class so I am going to give it a shot this year. My lab class is six students and we have access to two instruments, so I thought this might be a little on the short side. But then I thought about it and I do a few labs in which we use NaBH4 and NaBD4. That gave me the idea of including these compounds in the lab too. It will set up the other labs I do very nicely and it will give the students a first shot at making KBr pellets. I don't care so much about the organic functional group aspect, so that is not a concern. I'll let you know how it goes.

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