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Abstract
From the studies of infrared and Raman spectra and X-ray diffraction, it was found that myristic and palmitic acids crystallized into a new form (referred to as A 2) different from the already-known A -super and A 1 forms. The polymethylene part of the molecules comprises the triclinic polyethylene type sublattice. The unit cell consists of two types of dimer chains that are different from each other in the conformation of the carboxyl groups. As the temperature decreases the A 2 form transforms into another A-type modification (A3) at about 140 K. The phase transition occurs reversibly accompanied by drastic changes in the infrared absorptions associated with the carboxyl groups.