Mass Spectra of Some Common Organic Molecules

View the mass spec for each of the molecules below by clicking on the chemical name. A plot of ion intensity (y-axis) versus the mass to charge ratio for the ion (x-axis) appears. The larger the peak, the greater the number of fragments with that molecular weight. (Because the ions usually have a +1 charge, the x axis directly measures the mass of each fragment.) The peak with the highest mass usually represents the molecular weight for the molecule.

See also Mass Spectra of Elements

Assignment: You have been assigned an organic unknown from among the compounds below. Compare the molecular weights from the mass spectra to your experimentally determined molecular weight, and decide which of the compounds shown is your unknown. Briefly justify your choice, and be sure to include the structural formula and name of the molecule, and the structures of important fragments in your writeup.

Note: On any displayed plot, you can click the numbered peaks to view an animation of the ionization process for that peak.







  Benzoic Acid




  Salicylic Acid


  2,4 - dinitrochlorobenzene




  Phenyl Benzoate


  2,4 - dinitrotoluene




  1 - bromo - 4 - chlorobenzene