# Which organic compound's NMR and IR are these? Can't find out. (Data available: Melting Point ~ 116 °C)

Which organic compound's NMR and IR are these? I have figured out that the compound is a 1,4 substituted benzene. And the substituents are probably not -COOH and -OH from the spectroscopy. Kindly help me in figuring the other groups out. (Data available: Melting Point ~ 116 °C, gives sooty flame)

• @Soumik Das: The presence of two clean doublets in aromatic reagion of NMR would not agree with your suggestion. It may be 4-nitrophenol, which has $113-114$ $\mathrm{^0C}$ melting point. – Mathew Mahindaratne Jan 28 '19 at 16:38
• The very strong signal at ~1350 would fit for C-NO2 – Waylander Jan 28 '19 at 21:25
• Why is there no C-H stretch band in the IR spectrum near 3000 $\ce{cm^{-1}}$ ? – Shoubhik R Maiti Jan 28 '19 at 21:41
• @pas — When you present an NMR spectrum, you absolutely need to also give the nucleus, the frequency and the solvent. Nevertheless, I agree with Mathew on the 4-nitrophenol. The chemical shift of OH group can vary A LOT depending on the solvent, the temperature and the pH which, in turn, depends on the concentration. In this case, p-nitrophenol is acidic, so the more concentrated it is in the NMR tube, the more acidic the pH and the more the signal will move to the left. – SteffX Jan 29 '19 at 13:20
• @MathewMahindaratne The signals of 1,4-substituted benzenes form a AA'XX' system; so despite their appearance for this sample and measurement they do not qualify as simple doublets. – Buttonwood Jul 21 '19 at 21:36

The integrals and shifts in the very simple NMR spectrum are a giveaway that this is a simple compound with two different types of aromatic signal, and another non-aromatic signal from a substituent, at a 2:1 peak integral ratio, hence possibly a para-disubstituted benzene ring with one proton in one substituent, none on the other.

The IR spectrum is practically identical to that in the NIST webbook for p-nitrophenol. Some other clues:

• Oop Signal at $$\pu{800 cm^-1}$$: para substitution
• $$\pu{1400-1600cm^-1}$$: aromatic cc stretch, matches nicely with typical appearance for para substitution
• No peak at $$\pu{1700cm^-1}$$: no carbonyl
• Weak signals at $$\pu{3000cm^-1}$$: sp2 stretch, no sp3
• Signals at $$\pu{1350 and 1500cm^-1}$$ may be nitro

Note this is a little tricky - a search would show some variation in reported spectra.

The melting point also matches reported values.

This is well in agreement with many of the comments under the original post.