Real-time Raman spectra of shock compressed benzene and its monosubstitutes, iodobenzene, and nitrobenzene, have been measured in the pressure range up to 7.5 GPa. Spectral peaks show almost linear blueshifts against shock pressure. However, nitrobenzene, compared to the other two compounds, shows smaller shifts. Especially the increase in Raman frequency of the NO2 stretching mode (1346 cm-1) is extremely small. An intermolecular interaction between nitrobenzene molecules seems responsible for this behavior.