Organic Chemistry question about NMR

[DoctorWannaBe]

I'm taking an Organic Chemistry lab and the first assignment is about NMR. I never had much training about NMR in my lecture classes (I've taken both semesters of OChem lecture), so I'm having trouble with the problem set. How do you go about drawing an NMR, for example toluene? Do you just identify how many different kinds of hydrogens there are and look up in a table where the peak should be, and draw the appropriate splitting? How do you know how tall to draw the peak, or whether something should be more upfield/downfield? And does anyone know of a website that will allow you to type in the name/formula of something and view the NMR so I can make sure I'm doing it right? Sorry for so many questions, but my TA didn't give us any help, and my book isn't too helpful either.

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[ItsGavinC]

Okay, I'll share my secret website with you. It allows you to search compounds based on NMR and to type in names to view carbon or hydrogen NMRs. I used it quite a bit for identifying/confirming unknowns in my organic lab.

http://www.aist.go.jp/RIODB/SDBS/menu-e.html

 

[DoctorWannaBe]

Thanks so much for that website. That's what I was looking for, and I hope it will have most of what I need. Do you know a way to make it list the integration numbers and/or make the splitting more clear? I tried a few examples and it is hard to see the splitting, even it is is only a triplet.

 

[YaFwiendToluene]

well, first of all...you will have to be familiar with ur NMR chart...and where certain signals appear....so...for example...If I were to predict the readout for toluene(methyl benzene) .....1) I know that a phenyl group occurs at about 7.5-8 ppm as a "multiplet" right? so then..I take a look at the constituent(s)....it has 1 constituent...a methyl group. A methyl group is a Carbon with 3 Hydrogen atoms attacthed to it.....the 3 hydrogen atoms are all in the same "field" or in simpler terms...."they are all equivalent w/ no electron withdrawing group having a SINGLE effect on it. The signal for a methyl group most of the time will appear at approximately 4ppm....but since the aromatic ring is present...it will give that group a slight pull upfield ( 4.2-4.3ppm). Those two signals should be characteristic to Toluene.

The key to learning this is just to familarize yourself with ppm values for the diff groups....and to just get alot of practice. Using the website provided is fine.....but when you are confronted with a question like this on an exam(and you most likely will be)..then you will be in deep doo-doo.

Good Luck.