You are given an impure sample of a phenol and asked to purify it. You ask for i

Question

1. You are given an impure sample of a phenol and asked to purify it. You ask for information about the suspected impurities, but it seems no one really knows. So you ask for an IR/NMR spectra of the impure sample. Upon scrutinizing the IR spectrum carefully, you find that there is a small, but significant, signal at about 1700 cm-1, a small broad peak at about 3000 cm-1 and a much stronger broad peak centered at about 3580 cm-1. That gives you an idea about the nature of the impurity, so you scrutinize the 13C NMR spectrum, looking for a short signal at ~170 ppm- you find it. You then look for a signal in the 10-13 ppm range in the 1H NMR spectrum- there seems to be a little “blip†on the baseline at 11.5 ppm, but it is not very clear.What can you say about the nature of the impurities, based on the IR spectrum? How does the 13C NMR signal at 170 ppm support this conclusion? What were you looking for in the 10-13 ppm range in the 1H NMR spectrum? Explain your reasoning.

Explanation / Answer

3000 should be a rounded peak indicating your alcohol
3580 hints at a nitrogen compound such as an amine
1700 is going to be a double bond somewhere sometimes around 1600ish you get your benzene ring but later closer to 1700 you get a C=O bond show up

phenol = C6H5OH
if you have a C=O you've got problems so unless this teacher is satan I think all you should worry about is the possible NH2, NH3, NH4OH guys.

Take a small sample and add HCl to it...(you will probably get a white precipitant, ammonium chloride)
You could also smell your sample. pure phenol with smell like alcohol but amines smell nasty sometimes, nauseating! that's a sure fire way.

purification would probably pending previous tests result in precipitating out the N complex and filtering. Other methods might include a distillation ( alcohols boil off very quickly so it's an easy way to purify alcohols)

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