[Raginraj89]

Hi. For our lab, we need to identify an unknown compound using IR, Mass spec, H-NMR, and C-NMR. I' am terrible at analyzing this data so i was looking for some assistance. The mass spec data shows C: 54.9%, H: 4.61%, O: 31.34% and N: 9.15%. The compound i tested was a yellow powder. If you can help me, i can also send you a pdf of all the data. Thanks so much!

[w00tage19]

What are some of the important peaks/stretches in your IR/NMR/MS data?

[MOTOBALL]

I have to say that I'm not surprised that you have problems analyzing data, since you clearly don't know the difference between elemental composition data and a mass spectrum.

At least determine the empirical formula yourself as a start.

[pacifyer]

This problem is rather simple, kinda kindergarden chemistry, actually. No need of spectral data, I believe...

You just need to find the formula, which is C7H7NO3, then start thinking, use the hydrogen deficiency index, deduce it must be an aromatic compound, with an OMe and NO2 group... then search for properties of each isomer, and deduce that the only possible answer is... well, I can give you the answer for 50 bucks!!!



OK, this time for free: o-nitroanisole.

[Raginraj89]

This problem is rather simple, kinda kindergarden chemistry, actually. No need of spectral data, I believe...

You just need to find the formula, which is C7H7NO3, then start thinking, use the hydrogen deficiency index, deduce it must be an aromatic compound, with an OMe and NO2 group... then search for properties of each isomer, and deduce that the only possible answer is... well, I can give you the answer for 50 bucks!!!



OK, this time for free: o-nitroanisole.

Yeah i got the same empirical formula yesterday. Im just having a hard time finding the important peaks in the IR data. Theres a very sharp peak around 3520 cm-1 wavenumbers which i feel is uncharacteristic for this compound  .

[Raginraj89]

Finished up the IR data and mass spec data. Anybody have any tips on how to successfully analyze H-NMR and C-NMR?

[Raginraj89]

Im analyzing the C-NMR data and there are 5 peaks, which indicates that there are 5 different carbons in the compound? What happened to the other 2 carbons, that are not shown by the C-NMR data? I appreciate any help.

[democanarchis]

Im analyzing the C-NMR data and there are 5 peaks, which indicates that there are 5 different carbons in the compound? What happened to the other 2 carbons, that are not shown by the C-NMR data? I appreciate any help.

As this is a disubstituted aromatic ring, we have 2 quaternary carbons, which have a very weak 13C signal. They are probably obscured by the baseline, to see them you'd have to increase the concentration of your sample, the number of scans, and if possible use a NMR with a stronger magnet or move your probe closer

[Dan]

I don't see any evidence other than elemental analysis. I think assignment of any structure based on that evidence cannot be done with anything remotely close to certainty. There are quite a few isomers of C₇H₇NO₃...

o-nitroanisole is not consistent with 5 peaks in the ¹³C, the fact that you have 5 peaks could be due to a weak sample not picking up quaternaries, or we could assume the experiment was done properly... only 5 peaks could mean that there are 2 pairs of equivalent carbons, in which case p-nitroanisole could be a candidate. That said there is no convincing evidence presented for the presence of an aromatic ring at all. Post some spectra, or ot least give some nmr shifts...

[Raginraj89]

I don't see any evidence other than elemental analysis. I think assignment of any structure based on that evidence cannot be done with anything remotely close to certainty. There are quite a few isomers of C₇H₇NO₃...

o-nitroanisole is not consistent with 5 peaks in the ¹³C, the fact that you have 5 peaks could be due to a weak sample not picking up quaternaries, or we could assume the experiment was done properly... only 5 peaks could mean that there are 2 pairs of equivalent carbons, in which case p-nitroanisole could be a candidate. That said there is no convincing evidence presented for the presence of an aromatic ring at all. Post some spectra, or ot least give some nmr shifts...

This data was provided to us by our instructor so we had no control over how the experiment was done. Everything makes sense, except for the C-NMR data. All of the other data points towards o-nitroanisole as the unknown compound. Here is the data that was given to us:

[pacifyer]

Now, I see in the spectra a p-disubstituted pattern, in 1H as well as in 13C NMR. That is why you have 5 signals: two pairs are identical in the 13C spectrum. The ONLY substitution pattern that gives you two doublets in the 1H NMR, is p-disubstituted.
As a homework, use the MS data to confirm the structure. Look for M-15 (Me), M-31 (OMe), M-17 (OH), M-46 (NO2), etc.
You can also search in the IR spectrum if the substitution pattern appears, looking the overtones at 2000-1660 cm-1. If so, it would be another confirmation of structure.

[Dan]

Now, I see in the spectra a p-disubstituted pattern,

Agreed, but this is cannot be a nitroanisole. Notice the relative integrations in the ¹H nmr - 4H aromatic then a 2H and 1H - there is no evidence for a methyl group here. DEPT (to find CH₂) and HMQC (to find OH) would be helpful - but based on the IR peak in the OH region mentioned earlier by the original poster and the typical CH₂OH in the ¹³C (~63 ppm) I suspect this is actually p-nitrobenzyl alcohol and not p-nitroanisole.

[Raginraj89]

Looking at the IR data, there is a sharp peak at 3510 cm-1 which indicates an OH (alcohol), so it cant be o-nitroanisole. Also, when I was performing the IR analysis, the unknown compound I used was a yellow grity powder (might help with identification of compound).

Edit: After going back and double checking everything, the unknown was determined to be 4-nitrobenzyl alcohol.

Thanks to everyone who helped out!

[pacifyer]