Thermodynamic Studies of Orientational Disorder in π-Molecular Compounds

Abstract

The heat capacity of naphthalene-tetracyanoethylene was determined from 5 to 300 K and the smoothed thermodynamic functions reported at selected temperatures over the region of measurement. A bifurcated peak was observed in the heat capacity near 160 K. This transition was attributed to the crystal structure change reported elsewhere. A second anomaly overlaps the high-temperature end of the bifurcated peak and extends to 240 K. The nature of this second transition cannot be conclusively determined, but probably arises from the onset of reorientational motion of the naphthalene molecules. From the absence of anomalies below 160 K, it was concluded that the motion observed by solid-state n.m.r. measurements near 77 K is naphthalene libration and not reorientation.