NMR & IR interpretation

[youngnflyy]

I remember someone asked about this a few weeks ago, but I can't seem to find the post. Could someone please give me a web tutorial, or website which explains interpreting NMR and IR.

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[mikeinsd]

i think i am the only person in the history of the world to do this... but seriously it can help...

most books have websites, many of which have online material that you can use for free! i did this a lot in biochem/mol bio because the books website has all the graphs and pictures and everything, except it is all animated and sweet and easy to follow...

so, i dunno which book you have, but go to the website (should be somewhere) and see if there are diagrams/tutorials online

 

[BlackSails]

I remember someone asked about this a few weeks ago, but I can't seem to find the post. Could someone please give me a web tutorial, or website which explains interpreting NMR and IR.

Do you want MRI or NMR? They are the same technology, but NMR spectroscopy looks a bit different than an MRI.

If you want an MRI, a good radiology site is http://www.med-ed.virginia.edu/courses/rad/

 

[pnoybballin]

This website will be your best friend when working in the lab. http://www.aist.go.jp/RIODB/SDBS/cgi-bin/cre_index.cgi

 

[novawildcat]

the easiest way to score quick points with NMR is 1.) count the number of hydrogen environments. This should tell you right off the bat how many signals you should see. 2.) use the n+1 rule.


with those two rules alone a lot of times you can figure out the chemical structure.



IR is basically the most worthless form of spectroscopy. The only thing you need to know from IR is C=O stretches and -OH stretches. Other than that, IR is worthless.

 

[CTtarheel]

IR is basically the most worthless form of spectroscopy. The only thing you need to know from IR is C=O stretches and -OH stretches. Other than that, IR is worthless.

but NMR won't be able to tell you definitively that your molecule has a carbonyl!
IR can also be useful in comparing ligand field strength in organometalic complexes.

novawildcat gives ood advice for NMR though:

Figure out the splitting for each hydrogen first, then you can generally assign hydrogen atoms closer to electronegative atoms or arromatic rings higher chemical shifts (though it works a little differently with H's on the arromatic ring).

 

[novawildcat]

but NMR won't be able to tell you definitively that your molecule has a carbonyl!
IR can also be useful in comparing ligand field strength in organometalic complexes.

novawildcat gives ood advice for NMR though:

Figure out the splitting for each hydrogen first, then you can generally assign hydrogen atoms closer to electronegative atoms or arromatic rings higher chemical shifts (though it works a little differently with H's on the arromatic ring).

NMR sure will. Aldehydes and carboxylic acids stick out like a sore thumb on a proton NMR spectrum. If you know you molecule (assuming that it is organic) has an oxygen in it then either A.) it is part of an alcohol B) part of an ether C) part of a carbonyl D.) part of an ester.

-OH is extremely easy to spot by NMR. from the chemical shifts of the signals it would be easy to tell if your molecule had an ether moiety. Once you rule those two out, your compound has to contain a carbonyl then. Once you get good at NMR, you can do all of that in about 15 seconds after your spectrum prints out.

 

[youngnflyy]

Thanks for the resources. Personally, I'm a big fan of mass spectra, however my lab professor gave us a stack of uknown compounds with their mass spectra, NMR, and IR to figure out what they are. He did a horrible job explaining NMR to us as it was the last thing we did in lab, so I'm just a little bit lost in terms of interpreting it. I can pretty much figure out what they are based on the mass spectra, but in the reports I have to label and explain what the bands on the NMR and IR represent.