Temperature effect on the single and double hydrogen atom transfer reactions in o-, m-and p-toluic acid butyl esters

The temperature effect on the single and double hydrogen atom transfer reactions in o-, m- and p-toluic acid n-butyl esters and isobutyl esters has been investigated. For the meta and para isomers, the abundance of the m/z 137 ion C₈H₉O₂]⁺ generated by a double hydrogen atom transfer reaction increases relative to the m/z 136 ion C₈H₈O₂]⁺˙ generated by a single hydrogen atom transfer reaction upon lowering the temperature of the ionization chamber. On the other hand, the ratio of the peak abundances 137]⁺/136]⁺ for the ortho isomers is nearly constant when the temperature is changed. It is shown that this is due to the difference between the appearance energies of the m/z 136 and m/z 137 ions.