S–H proton dissociation enthalpies of thiophenolic cation radicals: a DFT study

Abstract

The S–H proton dissociation enthalpies (PDEs) of para and meta substituted thiophenolic cation radicals were calculated by density functional theory (DFT) using (U)B3LYP functional on 6-31G(d,p) basis set. It was revealed first, DFT method could give acceptable S–H PDE, at least in a relative sense. Second, PDE was better than other parameters, such as bond length, bond stretching frequency, spin density and charge difference, to characterize the proton dissociation process, because it was absolutely effective for comparison between phenolic and thiophenolic cations. Finally, electron-donating groups raised the S–H PDE and electron-withdrawing groups reduced the parameter, which was opposite to the electronic effect on S–H bond dissociation enthalpies (BDEs). And the electronic effect on S–H PDE was much stronger than that on S–H BDE. The difference resulted from the distinct electronic effects on stabilities of thiophenolic cation radical and parent thiophenol.