[Violagirl]

Hi I was wondering if somebody could check to see if I was on the right track with determining the peaks in my IR and NMR spectrums of methyl 3-nitrobenzoate?

For the IR, I think I figured out most of the peaks but wasn't sure about a few. Methylene chloride was used along with the product and was trying to figure out if some of the peaks that I was unable to determine belonged to it.

For the NMR, just was wondering if somebody could confirm if I was right about the identity of each of the peaks. Also, on determining integration values, does it work to just measure the peak in terms of area under the curve with a ruler? Any help is appreciated!

[Violagirl]

So in trying to figure out the integration values, one value I measured out with a ruler along the integration line where Hb is at, I measured it out to be 3.1 cm long. Thus, this would be the integration value of the tallest peak and could be used as a value for final analysis right?

[Vidya]

Your NMR assignments are correct and IR is also correct.IN IR you need to specify the type of stretch - sp2 C-H or sp3 C-H stretch.

[Vidya]

I forgot to include about the integration--
For integration you need to take the ratio of the areas of each peak or integration can be calculated using the no of H  atoms for that peak
for example in your compound
Ha:Hb:Hc:Hd :He:: 3:1:1:1:1

[Violagirl]

Thanks so much for your input, it helped a lot and helped affirm the results that I got! 

I had one more question, with regard to using J values to determine if ortho and meta compounds are present or not. I obtained J values of 2 ,2 ,2 and 8 for different peaks in my NMR spectrum. When I went to look it up, J values of 2 relate to meta compounds as 8 relates to ortho. So since I obtained a great quantity of 2 for J values, that would argue for meta in my product right? If ortho was present, wouldn't each peak have greater J values to 8, that of ortho? Also, the substituents were ortho to one another, would the chemical shifts of the peaks be closer to one another or would that not impact anything? Any clarification on this would be great!

[orgopete]

From your spectrum, Hb and Hd stand out, integrate for 1H each so they are the easiest to identify. Granted that Hd appears as a triplet or doublet of doublets split by Hc and He and the coupling constants are equal or very nearly so. They don't have to exactly equal.

Hb is similar with couplings from Hc and He. There is a potential coupling from Hd, but para coupling can be very small or absent.

That leaves Hc and Hd. They overlap and give the peaks integrating for 2Hs. By difference, they are Hc and Hd, no question about it. If you drew the splitting diagram for either one, you would get a larger ortho coupling of 8Hz and two smaller couplings of ~2hz. By overlapping them, the larger coupling constant may be obscured, but it is still present.

[Violagirl]

That does help a lot, thank you! 

I know my professor wanted us to pay particular attention to the triplet peaks around 7.6 and 8.8. At Hd, I found a J value for 8 and at Hb, a value of 2. So in essence, the J value at Hb would argue for meta position of the substituents right? Wouldn't it also be a J value for 8 if it was otherwise ortho? I'm just not sure how to fully argue how the J values correspond to meta position other then that J value constants for ortho are normally 8 and for meta, normally 2.

[orgopete]

… At Hd, I found a J value for 8 and at Hb, a value of 2. So in essence, the J value at Hb would argue for meta position of the substituents right? Wouldn't it also be a J value for 8 if it was otherwise ortho? I'm just not sure how to fully argue how the J values correspond to meta position other then that J value constants for ortho are normally 8 and for meta, normally 2.

Just so we use the correct terminology, we don't use "meta position of the substituents" in referring to proton coupling. If the hydrogen atoms are meta to one another, their coupling constants will be at a characteristic small value (~1-4Hz). If the hydrogen atoms are ortho to one another, they will have a larger coupling constant (~6-10Hz).

The coupling constants tell you to regiochemical relationship that a given hydrogen has to other hydrogens in the molecule. Hb has a small coupling constant, therefore it does not have an adjacent hydrogen ortho to it. It does have a hydrogen meta to it, in fact two hydrogens meta. There is also one hydrogen para to it, but its coupling constant is so small, it is not splitting Hb.

I searched and found two examples of trisubstituted benzene rings in which the actual hydrogens can be deduced from their coupling constants. A meta-nitrobenzoate is more complicated because it is only disubstituted and two hydrogen absorptions overlap. None the less, one could draw a theoretical coupling diagram similar to the second example shown below.

[Violagirl]

Thanks again! So in trying to explain it again from my standpoint, at Hb for example, because it has a J value of 2this reflects the meta position and that no hydrogens are around it. at Hd, because it has a J value of 8, this shows it in the ortho position and has H
atoms next to it on the ring. Is this correct in terms of explaining it for J coupling?