[dlong13]

I'm having a lot of trouble deciphering this NMR and would REALLY appreciate some help. I performed an 1H-NMR on an unknown compound in DMSO.  Due to the IR and a 2,4-DNP test i know that I have a ketone and no other functional groups.  The IR also produced no c-h alkane stretches, only c-c aromatic stretches, the carbonyl stretch, and some other weak intensity stretches at 1282, 1168, 935, 806 and 691.

1H NMR shifts are:
2.5 s (DMSO)
3.35 s  int. of 5
7.95 d of d, int. 2
8.25 d of d, int. 2
(I chose the integration values of 5 for the singlet, and 2 for each of the doublet of doublets)


the d of d at ~8.25ppm is different than the 7.95 peak in that the intensities of the outer peaks are greater than that of the inner peaks, whereas in the 7.95 doublet of doublets, the intensity of each peak decreases as you're going upfield.

Another strange, probably inconsequential aspect of this proton nmr is that on the upfield-side of each d of d, there is a very weak peak VERY close, of intensity probably less than 1/10th of that of the doublet of doublet peaks.  I would've written it off as background noise but because a small peak appears on both d of ds, and actually on the singlet too, it makes me wonder if it is a diagnostic peak. Thoughts?

This is the first time I've used 1h nmr to identify an unknown so I'd really appreciate any help you guys can give me to elucidate the identity of this compound.

Thanks!

[bolo]

Doublet of doublets means 1,4-disubstitued benzene ring. The singlet of 5 hydrogens is although bit confusing to me.

[dlong13]

The 1,4-disubstituted benzene ring is two doublets slanting towards each other. Although my peaks are the correct distance apart, I have two doublets of doublets, not two doublets. What I'm confused about is why I have two separate doublet of doublets.  Are my two doublets of doublets masked as two separate 1,4-disubstituted benzene rings?  I'm fairly certain that the singlet at ~3.35 is due to a methyl group on a ketone due to a previous lab.

Thanks for your input, bolo

[bolo]

OK, 3.35 seems to me there should be a methylene group between benzene ring and a carbonyl group but the integration of 5 is not right in this case. Due to this, the separation of aromatic signals to two doublets of doublets suggests that there should be a "very EWG group" in the para position (if methylene group exist), such like nitro group. Could you shortly describe the reactions you have made? It would be much easier to predict the structure.

[dlong13]

Bolo,

The only reactions I did were making a derivative of the compound using 2,4-dinitrophenylhydrazine.  I was given this compound for the sole purpose of identifying it.  And my IR shows no other function groups.  Is it possible that I have a benzene ring with two neighboring protons, a COCH3 carbonyl group and the rest methyl groups?

[dlong13]

So I've continued working on this all day, and 9,10-anthraquinone has a mp of 284-284 (source: s-a), which exactly matches my experimental mp.  9,10-anthraquinone has no methyl groups... there are only eight protons, four of which are on each benzene ring.  So now instead of the doublets of doublets giving me a problem, the singlet is giving me a problem!  No proton on 9,10-anthraquinone is not split by a vicinal proton.

[bolo]

So it is simply anthraquinone. Singlet of ca. 5 at 3.35 ppm is from H₂O protons as they appear at about 3.33 ppm. Due to resonance, each signal of aromatic protons appears as doublet. That is why two doublets of doublets are observed. That's all.

bolo