The Fragment Ion C13H9O2 m/z 197 in the Mass Spectra of 2-(2′-R-phenyl)benzoic Acids

In the electron impact mass spectrum of 2-(2°-R-phenyl)benzoic acids where R=H, NO2, OCH3, COOH, or Br, an abundant fragment ion m/z 197 is formed by an ipso substitution in which R is expelled as a radical. The structure of the ion m/z 197 has been shown by collision-activated dissociation to be identical with that of the protonated molecule formed by methane chemical ionization of 6H-dibenzo[ b,d ]pyran-6-one.