Problem #8: The molecular formula for an unknown compound is C8H8O2. Data for the 1H NMR, 13C NMR, infrared and mass spectra for this compound are available by clicking on the buttons below; use the "Return" button to return to this screen. Help with the interpretation of each spectrum is available and you can review background and selected correlation tables by clicking on the links in the MENU above. Using the spectral and analytical information provided, determine the structure for this compound.

NMR Spectroscopy 

 

NMR Spectrum
Problem #8: C8H8O2

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 Problem #8: C8H8O2

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 Problem #8: C8H8O2
13C NMR: triplet: 43.8 ppm singlet: 135.0; three doublets: 127.3, 128.9, 129.9 ppm singlet: 178.0 ppm

Problem #8: C8H8O2

  • The molecule contains two oxygens, and from the analysis, contains five double bonds or rings. The large number of degrees of unsaturation strongly suggests an aromatic compound (DU = 4).
  • The mass spectrum displays a molecular ion and a base peak corresponding to a benzyl unit.
  • The 13C spectrum contains six peaks, indicating that the molecule has some elements of symmetry. The triplet at d 44 represents a CH2, flanked by electronegative groups. The peaks in the aromatic region strongly suggest monosubstitution, and there is a singlet at 178 which would be consistent with a carboxylic acid carbon.
  • The proton NMR also shows evidence for monosubstitution on an aromatic ring and a carboxylic acid proton. There is also an isolated CH2 which must be adjacent to electronegative groups.
  • The IR is highly reminiscent of a carboxylic acid. The broad peak at 3100 cm-1 represents the strongly hydrogen bonded acid OH, and it effectively masks the region around 300 cm-1.
  • The simplest structure which is consistent with all of these data would be a monosubstituted aromatic compound attached to a side-chain bearing a carboxylic acid.