Isomer effect in the branching ratio of anions for thermal electron attachment to chlorinated phenols

The temperature dependence of the formation of negative ions from chlorinated phenols was studied. For all compounds, Cl- was produced and the intensity of the chloride ion increased with the increasing number of Cl atoms present in the molecule. For some of them, (M-HCl)-, (M-H)-, and M- (M: parent molecule) were also observed. The intensities of the fragment ions such as Cl- and (M-HCl)-, increased with the increasing temperature, though that of the parent anion decreased. There may be two mechanisms to produce (M-HCl)-. One is the HCl elimination of the hydroxylic hydrogen atom and the ortho-Cl atom. The other is the HCl elimination followed by the migration of the hydroxylic hydrogen atom to the ortho position for the 3,4- and 3,5-dichlorophenols. The branching ratio of [(M-HCl)-]/[Cl-] depends on the length of the H---Cl bond of the intermediate for the former mechanism.