Condis Crystals of Small Molecules V. Solid State ¹³C NMR and Thermal Properties of N,N′-b/s(4-n-Octyloxybenzal)-1,4-Phenylenediamine (OOBPD)

Abstract

Motion in the condis and liquid crystalline phases of N,N′-bis(4-n-octyloxybenzai)-4-phenylenediamine (OOBPD) over the temperature range 187-431 K has been analyzed by solid state ¹³C nuclear magnetic resonance under the conditions of cross-polarization transfer and magic angle spinning (CP-MAS), and ¹³C spin-lattice relaxation times. The ¹³C γ-gauche effect indicated that even in the crystals of K3 (below 385 K) conformational disorder and motion exist in the paraffin chains. Also, below the first transition temperature (K3 to K2, at 385 K), coalescence of signals suggest 180° phenylene ring flips without increase in disorder (entropy). The mobilities are evaluated using the relaxation times of “C. Heat and entropy have been determined from 130 to 550 K. From a fit of the heat capacity at low temperature to an approximate vibrational spectrum, it could be derived that a large amount of conformational entropy is introduced gradually. Corrected thermal data are given for all phase transitions. A full accounting of order and motion could be made.

Key Words:

• N,N′-bis(4-n-octyloxybenzal)-1,4-phenylenediamine (OOBPD)
• condis state
• liquid crystal
• conformational motion
• solid state NMR
• γ-gauche effect of ¹³C
• nuclear spin-lattice relaxation
• DSC
• heat capacity
• entropy