This paper presents the results of measuring the frequency-dependent refractive index, the extinction coefficient, and the absorption coefficient of polar solutes (nitrobenzene, benzonitrile, and chlorobenzene) in non-polar solvents by using terahertz time-domain spectroscopy (THz-TDS) at room temperature. The intensities of the difference absorption spectra of the solution and the pure solvent show a specific peak for each particular solution. This finding demonstrates the potential application of THz-TDS in studying the microscopic details of a particular solute in solution. The low frequency spectra were analysed by using a model function for the time correlation function of the total dipole moment in order to understand the dynamics and the interactions in the systems. The picosecond exponential component was found to be less sensitive to the viscosity of the bulk solvent, and it is proposed that this component can be regarded as the result of structural relaxation in the solution. It was also found that the spectra of the benzonitrile solutions receive a large contribution from the Gaussian component, which is attributed to the librational motion. This suggests that the formation of dimers or oligomers might take place in the case of the benzonitrile solution.