Thiophenol (benzenethiol) ArSH as a derivative of phenol belongs to the sulfur-containing compounds whose importance in atmospheric, environmental, biological, and medical areas can hardly be overestimated.Moreover, the recent huge activity in nanoscience and nanotechnology has renewed the interest in these compounds, particularly in thiophenols and its derivatives, because of the ability of sulfur to bind metalic clusters [1-3].As yet, geometrical parameters and frequency assignment of halothiophenols are unknown. In this work theeffect of -F, -Cl, and -Br substitutions upon the geometry, vibrationalfrequency, andinfrared intensities of thiophenol is discussed. We also examined the intramolecular hydrogen bonding of ortho-substituted thiophenols and compared with that of phenols.In this study, the equilibrium geometry and vibrational frequency of titled compounds were computed with the GAUSSIAN 03 software program by using a selection of modern density functional, using B3LYP level. Naturalbond orbital analysis [4] was carried out using 6-311++G** basis set. The influence of solvent on compounds was studies using the Onsager model.The optimized geometry parameters and harmonic vibrational frequencies of halogenated thiophenols in the gas phase obtained at Density Functional Theory (B3LYP) level using 6-31G**, 6-311G**, and 6-311++G** basis sets. A comparison of the theoretical spectra of thiophenol with experimental data shows a rather good performance of the B3LYP/6-311++G**. The structural changes of the thiophenol ring are governed mainly by the electronegativity of the halogen atoms and, to a lesser extend, by resonance factors. All the vibrational normal modes of these compounds were assigned completely. The SH stretching, bending and torsional modes occupy a particular place among all the vibrational modes of thiophenol due to their extreme sensitivity to molecular environment. It was observed that the substitution effects on these frequencies. Also the energy differences obtained show that the strength of hydrogen bonding in the ortho-halothiophenols depends on type of substituted halogen atom and environmental conditions.

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