[Paabo]

Hey guys, this is my first post. I found this place after spending hours tearing my hair out, and then realized there surely must be people like me out there who despise unknowns as I do. So I come to you for help. I don't have a scanner, but I can describe for you the absorbancies of the IR, HNMR and CNMR.

IR: 3436, medium, broad (perhaps OH?)
1583, medium, sharp
1478, strong, sharp
1183, strong, sharpish (a bit broader)

CNMR: 150.5, 129, 126, 120, 118
             1       5     1     .5    3   <---intensities

HNMR:
7.39, 7.38 doublet
7.22, 7.20, 7.17, 7.16   qu   
7.04, 7.02, 7.00, 6.99   qu   (perhaps these two are actually 8 peaks together?)
2.81 singlet
2.07-2.03 qu

The compound itself is solid and white, and it reacted positively with the beilstein flame test. The melting point was approx. 41-43 degrees C, and the compound was soluble only in NaOH, but not H20, NaHCO3, or HCl. I did run a derivative on it, and got a solid which melts at approx. 100 degrees C. However, I think I may have gotten a contaminated product, so you may not want to take that into account.

I think it must be something like 3, 5-dichlorophenol.. what do you guys think?

[Paabo]

..or do you think it'd have to be an alcohol? Dammit, I'm so confused.

The solubility tests show that it must be acidic, but not too strongly so. Out of the main functionalities possible for the assignment, that leaves only phenols and alcohols.

[Squirmy]

The solubility tests show that it must be acidic, but not too strongly so. Out of the main functionalities possible for the assignment, that leaves only phenols and alcohols.

The solubility test should distinguish between a simple alcohol and a phenol. What exactly were your results?

Out of curiosity, what NMR solvent did you use? Acetone-d6, perhaps? You might find the big blue table of NMR on the following webpage helpful:

http://www.chemistry.nmsu.edu/Instrumentation/NMR_Solv.html

[Paabo]

If this helps, the CNMR looks nearly identical to this one

http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/cre_frame_disp.cgi?sdbsno=1383

However, the HNMR is off- instead of the singlet at 5, there should be one at ~3, and many clumped peaks at ~2.

[Paabo]

The solubility tests show that it must be acidic, but not too strongly so. Out of the main functionalities possible for the assignment, that leaves only phenols and alcohols.

The solubility test should distinguish between a simple alcohol and a phenol. What exactly were your results?

Out of curiosity, what NMR solvent did you use? Acetone-d6, perhaps? You might find the big blue table of NMR on the following webpage helpful:

http://www.chemistry.nmsu.edu/Instrumentation/NMR_Solv.html

  Hello, thanks for taking the time to try and help me.

The results of the solubility tests were stated in the first post: that it was only soluble in NaOH. This means it must be acidic- however, because it wasn't soluble in NaHCO3, that means that it can't be a strong acid such as a carboxylic one.

The solvents used in all of my NMR is CDCl3.

edit:
Also, the positive beilstein flame test points to it being halogenated.

[Squirmy]

A phenol is much more acidic than your average aliphatic alcohol (e.g. heptanol) due to resonance stabilization of the conjugate base. NaOH is a strong enough base to effect essentially complete deprotonation of a phenol (so, it becomes water soluble). Most aliphatic alcohols only form equilibrium amounts of the conjugate base in NaOH.

The 1H NMR signals at 2.8 and 2.07-2.03 were the basis of my question about NMR solvent. Looks very much like residual peak for acetone (a quintet at ~2.05) and HDO in acetone (singlet at 2.. Trying to include them in your analysis would confuse things, since they may not becoming from your unknown.

[Squirmy]

silly smileys...

in my last post "2."   = "2.8 )"

[Dolphinsiu]

Yes...actually I only want to the intergation number of proton nmr since the number of protons really can help structural elucidation.

[Paabo]

Hey guys; thanks for your responses. I still haven't made any headway here though, and I'm starting to freak out. I gotta know the identity of this unknown (one of 4), and I just can't figure it out. I got my hands on a scanner, so you guys can see first hand.

http://img7.imageshack.us/img7/9285/cnmr.jpg
http://img7.imageshack.us/img7/5506/hnmr.jpg
http://img25.imageshack.us/img25/7986/irspectrum.jpg

Check it out, let me know what you think. Is that huge spike to the right in the HNMR the solvent? If so, that might make this a lot easier. Thanks in advance.

[Paabo]

Guys, if that is indeed the solvent, I will feel like a right fool for not being able to figure out what the hell it is.

[Squirmy]

Based on the 13C peaks centered at 77ppm, the NMR solvent is indeed CDCl₃.

However, even without integrations, the signal at 2.05 is suspiciously large, imho. There's another way that acetone could find its way into your NMR tube...if the tube was cleaned with acetone (very common) and not all of it evaporated. Even if you dry acetone-rinsed tubes in an oven, it takes a surprisiingly long time for all of the acetone to evaporate (btw, drying in the oven is discouraged by NMR tube manufacturers).

[Paabo]

Hmm I'm thinking it would be very unlikely. The CNMR and HNMR were given to me by my professor after completing preliminary qual analysis. I think it must be out of a book or something; she wouldn't have messed this one up like that.

[Squirmy]

Oh, the NMR spectra were ones she had ready for you. The 13C has the parameters listed for the NMR experiment which includes the date it was run (Apr 6 2006), and I'd be shocked if any spectrum that recent came from a book. More likely, she ran the spectrum herself, but I can't imagine she made that mistake in my last post, didn't realize it, and then gave you the spectrum.

Maybe there's a simpler explanation: the residual solvent peak for CDCl3 comes at ~7.2 ppm. Maybe she switched to d6-acetone for the proton NMR to avoid overlap with your aromatic signals. The solvent & other parameters aren't listed for the 1H NMR, so who knows?

Regardless of how it happened, I now know what the compound is, and the peaks @ 2.05 and 2.8 are definitely not coming from the analyte.

An additional piece of info that may help:

In the aromatic region of the 1H NMR, there is some fine, long-range splitting (i.e. splitting from hydrogens more than 1 carbon away). If you ignore the fine splitting, you're left with a singlet @ 7.39, a doublet centered @ 7.20, and a doublet centered @ 7.02.

[Paabo]

So, I think it is 2,4-dichlorophenol. Am I going to fail if I pass in my report saying that? Everything you're telling me about my NMRs is jibberish, though I do appreciate the fact that you're trying to help me here. I'm not by any rights a chemistry guy; I'm a molecular biology major, man. Is there any way you can clarify what you're trying to tell me? Am I on the right track? Am I way off? Can I get a bone thrown here? I'm about to have a breakdown over this 4th and last unknown; I can't figure out why it's giving me so much trouble. I've spent the weekend working on my cell bio and genetics work, neglecting this project (which in hindsight was a very, very bad thing to do.) You were apparently able to figure it out pretty easily. What am I missing?

[Squirmy]

Everything you're telling me about my NMRs is jibberish

Sorry you feel this way. Good luck!