Chemical Forums

Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: wong.cst on May 15, 2011, 10:39:32 PM

Title: need help with NMR and IR spectrum.
Post by: wong.cst on May 15, 2011, 10:39:32 PM: hi! I am working on identifying an unknown compound based on IR and NMR.

I received an unknown with a MW of 188 and have performed IR run and received the NMR spectrum for this compound. I am getting stuck because although my NMR peaks were very distinct, the integration ratio does not match up with the peak assignments. I had a triplet with an integration ratio of 2.61, a quintet with 1, another triplet with 1.89, and a quartet with 1.7. I tried first rounding off the ratios to 3, 1, 2, and 2 respectively but the number of hydrogens seems to low for my MW, so I multiplied everything by 2, but now i have 5.2, 2, 3.78, and 3.44. After rounding it to 5, 2, 4, and 3, I tried to see if the total makes sense since I determined that my formula was probably C12H12O2 with a HDI of 5, which implies an aromatic ring. However, on my NMR, there is no signal between 7 and 8 ppm. Thus I am working on first determining my formula and I am following the CnH2n+2 rule and that there is no nitrogen in my structure since my MW is even.

I tried going back to my IR to check on the peaks and the most important peaks are the presence of both a O-H free hydroxyl and O-H h-bonded stretch, which would imply either an alcohol or phenol but again, I have no signal between 7 to 8 ppm on my NMR.

I am not sure what else I can do from here because the integration doesn't match up, and the IR peaks are very vague to my structure. I feel that perhaps I have a carboxylic acid or at least its derivative.

This report is due on Tuesday and I am waiting for my professor to email me back...if she even will. Thank you very much...
Title: Re: need help with NMR and IR spectrum.
Post by: fledarmus on May 16, 2011, 07:43:14 AM: If 3-1-2-2 seemed reasonable, why not double it to 6-2-4-4? Given your feeling that there might be a carboxyl derivative, what might a doubling of the hydrogens imply about the symmetry of the molecule?
Title: Re: need help with NMR and IR spectrum.
Post by: dunno260 on May 16, 2011, 02:53:17 PM: Can you give shifts of major peaks in the IR and the shifts of the NMR spectra (even better would be pictures of both).