In this work we developed a method of laser spectroscopy to study the frequency shift of Mandelshtam-Brillouin components in the fine structure of Reyleigh line, which are origin due to the pressure fluctuations. The method allows to study a character of hypersound (~109 Hz)propagation in a critical region of a thermodynamic instability. Analysis of a complex of experimental material , presented in the paper, allows one to conclude that in aqueous solutions of non-electrolytes at critical concentration there is a whole structural transformations in solutions at the singular point temperature in “temperature-concentration” coordinate
