Infrared spectroscopy was used to study the structural phase transitions of laurylammonium chloride in the temperature range from 290 to 365K. it was shown that there is a solid-solid phase transition at 339K with a pre-transition at 327K. the infrared spectra inicated that virgin crystals at room temperature form a welloredred phase with all-trans hydrocarbon chains, and the lengths of N-H-Clhydrog4en bonds are different. the spectra suggested that the gauche conformers begin to appear at temperature above 327K. the spectra at high temperature over 339K demonstrated that the interaction between the chains decreases , the parcial "melting" of the chains is obvious , and the hydrogen bonds (N-H-Cl)have the same lengths.the main transition and pre-transition are mainly assigned to the intramolecular and intermolecular order-disorder changes respectivel.

Key words: INFRARED SPECTROPHOTOMETRY, CRYSTAL STRUCTURE, X-RAY DIFFRACTION ANALYSIS, HYDROCHLORIC ACID, PHASE TRANSFORMATION, LAURIC ACID P, TEMPERATURE EFFECT, CONFORMATION, AMINE SALT