Vibrational study on structural transitions of potassium pelargonate CH3(CH2)7CO2K

Anhydrous potassium pelargonate (KC9) undergoes four thermal transitions from room temperature to 450 degrees C. A normal mode analysis was made for the molecule in phase I at room temperature and the molecule was considered to have an all-trains conformation. With increasing temperature, partial melting of the alkyl chains occurred in phase II and complete melting was observed in phase III, as confirmed by vibrational spectra. In addition, orientational disorder of the carboxylate groups was suggested in phase II. This transition behavior of potassium pelargonate was compared with the behavior of nonane and pelargonic acid.