Abstract: | Several 1-X-sabstitirted-3-methoxy-4-trideuteromethoxybenzens were synthesized and their electron impact ionization mass spectra were measured with an ionizing energy of 20 eV. From the peak intensity ratio of M ? CD3 ] and M ? CH3] the fragmentation-directing ability of the substituent X was evaluated. The most powerful group was found to be NH2, which expelled a methoxy methyl group only from its para position. The CH3 group and four halogen atoms, F, Cl, Br and I, exerted a moderate effect Electron-withdrawing groups such as NO2, CHO and CN had only a little influence on the fragmentation selectivity. These results were interpreted in terms of the effect of X on the distribution of both the unpaired electron and the positive charge in the molecular ion. |