[Vardarac]

My organic chemistry lab assignment was to perform tests on an unknown substance in order to identify it. Most of the ones we ran gave very clear results, but one was rather ambiguous: A ceric ammonium nitrate test on the substance in solution caused a colorless precipitate to form. A color change of the solution, or a colored precipitate, were predicted by my textbook- but a colorless precipitate formed in a solution the same color as the ceric ammonium nitrate solution.

The compound was water soluble and acidic. I have attached its IR and NMR spectra below, if that helps. If you need more information on the compound, I will be glad to supply it.

Barring the fingerprint region, the compound also appears to have IR peaks in places not listed in my textbook, conveniently enough.

Help would be greatly appreciated. I am a little overwhelmed at the moment.

[orgopete]

Ceric ammonium nitrate is an oxidant, and the color changes refer to oxidation reactions. I'd call that a negative result.

The IR agrees with you physical properties. You should measure the integral from your NMR spectrum. That will give you a ratio of the number of different types of hydrogens present in you molecule. Since it is not recorded as an electronic value, you can use a ruler to measure the displacement up from the baseline in mm. That will give you a ratio of X mm: Y mm. X + Y = total number of hydrogens. Y/X will give you a ratio of the hydrogens of different chemical shifts. You should consult a chemical shift table to establish the types of hydrogens present. Also remember that X + Y = even number if you compound contains C,H,&O.

[Vardarac]

Thanks very much orgopete! You said that the IR agrees with the physical properties of this solid- Could you offer me any tips on how I should analyze the spectrum?

[orgopete]

Because I have experience, I did not have to make the comparisons that I will suggest. For IR spectra, I had used a book that listed the structural features with each band, but it also had example spectra. That is how I like to think.

For your IR spectrum, look to see if you have any of the characteristic stretching frequencies for different functional groups. I can see one functional group that is fairly easy to identify. Hint, your compound contains two oxygen atoms. 

For your NMR spectrum, what group or groups can you identify from a chemical shift table? The integral shows two peaks. As I indicated earlier, the sum must be an even number. If the peak with the greatest chemical shift is one hydrogen, the other group of peaks must be an odd number, 1, 3, 5, 7, etc. By measuring the height, you should determine that one of those is in better agreement than the others.

If you were trying to identify your compound by joining the pieces you have identified, it will be like building something out of Tinker Toys. From the information you have before you, there will only be one possible structure. 

If you lab book doesn't have your compound to compare with your spectra, you can go to SDBS to find it.