The kinetics of the first-order solid-solid structural phase transition in monodisperse n-alkane samples of odd tricosane C23H48 was studied by FTIR spectroscopy. The detailed study of the structure rearrangements of long-chain molecular crystals of n-alkanes during solid-state transitions has been carried out and the existence of many irregular conformers in solid phases of tricosane, the concentration of which reaches a maximum when approaching the  melting point, has been demonstrated. The presence of these conformational defects has been found to promote the development of a new phase in the bulk of the initial one and to facilitate the transitions between different  intermediate rotator phases in the solid state. Thus, the significant role has been demonstrated for the appearance of various intramolecular conformational defects during heating of n-alkanes, which promote interfacial transitions from the solid to the liquid state, weakening the intermolecular interaction and increasing the freedom degree of molecules.