Graduate Thesis Or Dissertation
 

X-ray photoelectron spectroscopy of trifluoromethylbenzenes and chlorofluoromethanes

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  • The core-electron ionization potentials for mono- and di(trifluoromethyl)benzene, for chlorofluoromethanes and for chlorine have been measured in order to give information on the electron distribution in these molecules and to investigate differences between the inductive effect of fluorine and that of CF3. For trifluoromethylbenzene the measured ionization potentials in eV are: F(ls), 693.88; C(ls, ring), 291.02; C(ls, CF₃), 298.24. For 1,3-di(trifluoromethyl)benzene: F(ls), 694.14; C(ls, ring), 291.48; C(ls, CF₃), 298.64. For 1,4-di(trifluoromethyl)benzene: F(ls), 694.17; C(ls, ring), 291.48; C(ls, CF₃), 298.58. For chlorotrifluoromethane: F(ls), 695.04; C(ls), 300.31; C1(2s), 278.84. For dichlorodifluoromethane: F(ls), 694.68; C(ls), 298.93; C1(2s), 278.63. For fluorotrichloromethane: F(ls), 694.33; C(ls), 297.54; C1(2s), 278.24. For chlorine: C1(2s), 278.74. Comparison of our gas-phase measurements with those made in condensed phases show that most of the difference between the two kinds of measurements is accounted for by a work function correction. A point-charge analysis of the core binding energy shifts shows that the carbon adjacent to the CF₃ group is negative, in agreement with theoretical predictions and with the results of similar experiments on aliphatic compounds. More surprising is the conclusion that the CF₃ group donates electrons to the ring. The well-known inductive effect of CF₃ results not because CF₃ withdraws electrons from its neighbors but because the positive dipole. of CF₃ creates a positive potential on the adjacent atoms. The core binding energy shifts of the chlorofluoromethanes point out deficiencies in using a point-charge model. Either relaxation energy corrections or a quadratic term in charge improves the model. It is noted that the chemical properties of these molecules correlate well with the core binding energy shifts, which are a measure of the potential at a given atom.
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