Gas-phase ionization and attachment energy (IE and AE) values of some p-and o-cyano derivatives of anisole and thioanisole (p-NCPhXCH 3 , X ) O, S; and o-NCPhXR, X ) O, R ) CH 3 ; X ) S, R ) H, CH 3 , and C(CH 3 ) 3 ) have been determined experimentally. The assignments of the spectra, based on those of the parent compounds PhXMe, NCPh, and XMe 2 (Me ) CH 3 ), agree with the results of theoretical HF/6-31G** calculations. The calculations correctly reproduce the prevalence of the planar rotamer of the oxy derivatives with respect to the gauche one, while overestimating the relative stability of the gauche conformer of the thio derivatives. The two rotamers of the thio derivatives have similar energy and their valence energy levels do not sizably differ. In addition, PhSMe and p-NCPhSMe have HOMO-LUMO energy gaps (<9.0 eV) smaller than the corresponding value (>9.5 eV) in the oxy derivatives and there are indications that the methylthio group has larger polarizability than the methoxy group. These data suggest that poly(p-phenylene sulfide) is more suitable than poly(p-phenylene oxide) to carry electricity under mild doping.