Raman spectroscopy was used to study the molecular relaxation processes in sulfates Li2SO4, Na2SO4, K2SO4, carbonates Li2CO3, Na2CO3, K2CO3, perchlorates NaClO4, KClO4 and nitrates Ca(NO3)2, Sr(NO3)2, Ba(NO3)2. It has been established that in the systems under study, phase transitions of the first kind are stretched in nature (diffuse phase transition): in sulfates, carbonates and perchlorates they are structural phase transitions, and in nitrates this is a crystal-melt phase transition. The existence of a pre-transition region was found in all the crystals studied.