Orgo Chem- Mass Spec. & NMR ??????

[armanda1]

Can anyone help me please?I have read these two subjects chapters twice for Orgo chem and I still have no idea what is going on? Can anyone shed some light as to what I am suppose to have grasped by now? I have midterm next week and I am terrified. Thanks Alot. 🙁

[UCLABruin]

If you were given a proton NMR or a carbon NMR, would you be able to determine the structure? It’s hard to give advice without knowing exactly what you are struggling with. Just remember to ALWAYS count the number of carbons and then count the peaks. That way, you know if there are any doublets, triplets, etc. Will you be provided with a reference sheet with the values for different functional groups in HNMR and CNMR? I think I can help you, but I need more info. 🙂

[efex101]

Also remember to look for different “types” of protons on NMR. For example (MCAT question here) if you had CH3-C=O-CH3 how many proton spectra would you have? only one because the protons are the same although they are on the molecule on two different spots. Think big picture and it will help, once you have the big picture go into details if your professor requires it. Good luck!

[armanda1]

Thanks for teh reply…I have looked at the examples they have given and I just can’t see how they take –let’s say –ethane and apply to those peaks…I am given questions like: how do u distinguish the mass spectrum of 2,2-dimethylpropane from those of pentane and 2-methylbutane? I sit there like- how am I suppose to correlate the two? what previous chapters can I refer to even have a single idea on where I am suppose to even begin? I have Bruice textbook for Orgo and usually everything is understandable once read –this is the hugest stump I have ever encountered….I don’t know anymore but I know I just can’t throw in the towel . I am taking Physics as well and it’s stressing me that I can’t grasp one to make me comfortable to try and focus on the other that requires the same about of effort. Thanks alot.

[lalee]

Hi Amanda,
You need to find a reference sheet for the peaks. Next you need to draw the structures, for instance, ethane CH3CH3 should have a quartet around 0.9 that integrates to 6 (for proton NMR). 2,2 dimethylpropane will have a CH3CH(CH3)2CH3CH3CH3 will have a -CH- peak (multiplet) around 1.4 or so (I think). Pentane will have just -CH2 and -CH3 peaks. Remember the number of peaks (n+1) tells you the number of hydrogens are on adjacent carbons…a triplet would have a neihboring carbon with 2 hydrogens, a doublet would have a neighbor with 1 hydrogen, etc.
I hope this helps a little! :boggled:
I know what you’re going through…I’m taking Ochem 2 and physics 2 this semester also! :banghead:
Good luck!
Laurie

[lalee]

p.s.
Just a note that my numbers may not be 100% accurate…I’m getting them from my head, not my notes! That’s why a reference sheet is important. Our professor let us use a reference sheet for IR, Carbon 13 NMR and proton NMR. Just too many different numbers to try to memorize! :yikes:
Good luck!

[cafe ahnan]

Hi. Just want to share a few sites that I found helpful when I was studying. In fact, I had a really good professor, and these are his notes:

http://gopher.chem.uic.edu/organic/MS.pdf
http://homework.chem.uic.edu/NEXT.HTM#

I think the important thing is to get the big picture, as another poster mentioned. You have to look at them like puzzles, if you have two molecules, try and see what is different between them, and piece together the puzzle.

Also I think it may be difficult to comprehend if you do not understand the background of NMR – check the sites and see if the background information helps you. Good luck.

[Author]

Posts