[Serenity_19]

For a class we have to determine an unknown of a poly functional group.

I've tried my hardest to figure this out, but I honestly don't know where to start:
Here is what I know:
Solubility: Weak acid (but being a polyfunctional group, I don't believe this one bit)
IR: (see image 3) this type of peak is at ~3300, and there is one additional peak at 1609. This makes me think of either an amine with a C=C or an amide.
NMR: This one is tricky. My original nmr (in class) showed a peak at 12.75, but I'm not sure if that's true since the NMR I have on my computer doesn't (the other peaks are fine, just not entirely sure about the 12.75 peak) -- the carboxylic acid test (Sodium Bicarbonate) did not have gaseous bubbles, but it changed the solution color and formed a precipitate.

Here are helpful images of the H NMR:




I initially thought it would have a benzene ring, because of that peak between 7-8 ppm, but I'm starting to think it's a secondary amine. Again, that conflicting peak at 12.75 scares me since only a carboxylic acid shows up in that area. Being all singlets, I do know that all the hydrogens are separated, but what I am guessing is that there are 4 hydrogens that are identical (for the 2.5 ppm peak). I'm also not sure about the 1.70 HDO peak. Is this really a solvent (since CDCl3 was used)?

I'm not looking for someone to give me the answer and tell me that I have X organic compound. I don't even want the answer. I just want a small push in some direction because at this point, I've asked friends and the TA and no one knows what's up.

[OrgXemProf]

Some random thoughts:

1. The two one-proton signals at delta 7.64 and 6.38 each appear to be more complicated than "singlets". Could these two protons instead comprise an AX pattern (two doublets, small coupling constant) that correspond to two tightly coupled aromatic protons?

2. A one proton singlet appears to be superimposed upon the upper half of the AB pattern centered at delta 6.38. This could be a third aromatic proton that occupies a position on a benzene ring that isolated from the other two (coupled) aromatic protons and thus displays no indication of H-H coupling. If so, this suggests that the unknown compound might contain a trisubstituted benzene ring.

3. The presence of phenolic or enolic O-H is consistent with the results of the solubility test ("weak acid") and also with the given IR information, i. e., broad, hydrogen-bonded O-H stretch around 3300 cm^-1 and absorption at 1609 cm^-1 (aromatic C=C stretch).

4. This leaves the singlet at delta 5.76, perhaps due to an (exchangeable) phenolic or enolic O-H proton.

5. The proton NMR spectrum of phenol may serve as a model for chemical shifts [see http://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi, SDBS No. 554, which displays a complex pattern due to aromatic proton absorption signals in the range delta 6.83 to 7.84 and an OH singlet at delta 5.35].

6. Then, there's that pesky four-proton singlet at delta 2.56, which is consistent with X-CH₂CH₂-X where X could be ketone C=O groups. Alternatively, these methylene protons might be situated in the aliphatic portion of a substituted benzocyclobutane (or maybe something else??)

7. The foregoing suggests that all aliphatic CH₂ protons in the unknown compound are magnetically equivalent. This requires the (weakly acidic) OH group to occupy position that maintains X-CH₂CH₂-X symmetry.

8. Can you suggest a structure that's consistent with the foregoing observations?

9. Hey, I didn't promise you a rose garden.

[Serenity_19]

Thanks Prof.
I took a closer look at the nmr and saw this:
                             

Is the first one a triplet of doublets?

[OrgXemProf]

Nope. Not a triplet of doublets (nor a doublet of triplets). And we know this because?

(1) Relative peak intensities for multiplets produced via spin-spin coupling of a nucleus to N equivalent nuclei can be determined using Pascal's triangle. Thus, a triplet would display three equally spaced peaks with relative intensities 1:2:1. This does not appear to be the situation with the absorption signals located in the region delta 6.36 - 6.40.

(2) The foregoing applies to first-order splitting patterns. However, a "higher-order" splitting pattern occurs when chemical shift difference (Hz) is much less or the same that order of magnitude as the J-coupling i. e., delta nu (Hz) divided by J (Hz) is less than or equal to 8, where delta nu is the chemical shift difference between coupled nuclei.

In this situation a second order pattern is observed, which results in "leaning" of a classical pattern. This is called the “roof effect.” 

Roofing is observed in the region delta 6.36 -6.40. Thus, the two downfield signals (both are apparent doublets) appear to "point upfield", while the upfield signal (another apparent doublet) "points downfield".  Since the direction of "roofing" provides a clue to the relative positions of coupled nuclei, this second-order effect can be quite useful when applied to analysis of complex spectra.

For additional information and examples of the roof effect please consult the following URL:

http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Nuclear_Magnetic_Resonance/NMR%3A_Experimental/NMR%3A_Interpretation
 
I find it difficult to rationalize the observed roofing pattern for the two-proton signals located in the region delta 6.36-6.40 in terms of two magnetically equivalent protons split into a "doubled triplet" (or, for that matter, a "tripled doublet"). Instead, might it be worthwhile to consider that these two-proton signals represent two magnetically nonequivalent protons that are coupled to a third proton?

And then there's the question of the two-proton absorption signal in the region delta 7.62-7.64. You will need to decide whether these peaks correspond to two one-proton singlets or, instead, to one two-proton doublet.

Back to the drawing board.

[Serenity_19]

I played around with MestReNova, and realized that it did not show carboxylic acid peaks for whatever reason -- hence why the peak at 12.XX ppm was not showing up in the nmr above:
Here is the actual ir and H nmr:

IR:


H NMR:

What's confusing me is that carboxylic acid peak in the nmr, but there isn't a carbonyl peak in the ir at 17XX cm-1 suggesting it.

What I think is that I have a carboxylic acid that has an amide somewhere. The peaks between 7-8 ppm suggests an aromatic.

From my understanding that peak at 1603 cm-1 can be either a C=C or an amide C=O
Hmm, could it be an indole with the N being attached to a carboxylic acid?

[Serenity_19]

(Just to put my thoughts out)

From the integrations:
1 H @ 12.69 ppm (singlet)
1 H next to another H (doublet) @ 7.6 ppm
2 H next to another H (doublet) @ 6.3 ppm
1 H @ 5.8 ppm (singlet)
3 H @ 2.56-2.64 ppm; unsure about the pattern
1 H @ 1.7 ppm (singlet)

Total: 9 H

7.52 has a small notch, but I think it's an impurity?
7.25 is CDCl3
3.89 has a small notch, but I think it's an impurity
1.6 doesn't seem to be part of 1.70, so it could
TMS at 0

I'll think up a structure later on today revolving around what we know from the NMR