Fragmentation and mass spectra of Aliphatic Acids

• Molecular ion peak is weak but noticeable.
• In short chain acids, cleavage of bonds next to C=O results prominent peaks at M-OH and M-CO₂H.
• In long chain acids, the spectrum consists of two series of peaks resulting from cleavage at each C-C bond with retention of charge either on the Oxygen containing fragment or the alkyl containing fragment.
• The most characteristic peak is m/z 60 resulting from the McLafferty rearrangement. Branching at α carbon enhance this cleavage.
  

lets examine spectrum of decanoic acid