Phase Transitions and Nonplanar Conformers in Crystalline n-Alkanes.

Crystals of n-alkanes show a remarkable series of solid-solid phase transitions. In the odd n-alkanes C(25), C(27), and C(29) a previously unknown transition is found by both calorimetry and infrared spectroscopy. The ubiquitous presence of nonplanar conformations of the chains is shown by infrared spectroscopy. The nonplanar conformers constitute approximately half the molecules in the highest temperature solid phase of C(29).