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-CH
2CH
2-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 CH
2 protons in the unknown compound are magnetically equivalent. This requires the (weakly acidic) OH group to occupy position that maintains X-CH
2CH
2-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.