We present a detailed computational study of the geometric structure and torsional potential of 1-phenylpyrrole, 2,5-dimethyl-1-phenylpyrrole. 3.4-bis(methylsulfanyl)-1-phenylpyrrole, and 3,4-bis(methylsulfanyl)-2,5-dimethyl- 1-phenylpyrrole. Both the neutral molecule and the corresponding radical cation are investigated for each compound. Calculations of the neutral species and radical cations are performed at the RHF/6-31G(d) and UHF/6-31G(d) levels, respectively, Our study has two major aims: (i) to assess and evaluate the effects of the bulky methyl substituents at 2,5 positions and (ii) to investigate the effects exerted by the electron-donating methylsulfanyl groups. The analysis of the results has revealed that both the methyl and methylsulfanyl substituents induce unusual structural properties, particularly in the radical cations.