THERMODYNAMIC PROPERTIES OF HEPTACYCLOTETRADECANE C14H16

Thermodynamic properties of heptacyclo[6.6.02.6.03.13.04.11.05.9.010.14]tetradecane (HCTD) are studied in this work. The molar enthalpy of combustion, found in five experiments is ΔcHom(cr, 298.15 K) = -(7743.25 ± 2.65) kJ·mol-1, and the molar enthalpy of formation is ΔfHom(cr, 298.15 K) = -(52.59 ± 3.27) kJ·mol-1. The molar enthalpy of sublimation of HCTD was measured with a heat-conduction differential microcalorimeter: ΔsubHom(333.8 K) = (77.99 ± 0.38) kJ·mol-1. The value ΔsubHom(298.15 K) = (79.29 ± 0.39) kJ·mol-1 was obtained using the difference between heat capacities of crystal and gas. Vapour pressure of HCTD was measured by the integral effusion Knudsen method in the range T = 298 K to 349 K. As a result we obtained the equation: In(p/Pa) = -(10078 ± 146)(K/T) + (33.64 ± 0.45). The weighted average value of the molar sublimation enthalpy: ΔsubHom(298.15 K) = (79.78 ± 1.63) kJ·mol-1 was used to calculate the molar enthalpy of formation of gaseous HCTD: ΔfHom(g, 298.15 K) = (27.19 ± 3.65) kJ·mol-1. The heat capacity of HCTD was measured by vacuum adiabatic calorimetry (T = 5 K to 304 K) and by the triple heat-bridge method (T = 300 K to 500 K). One solid-to-solid transition was discovered at T = 355 K with molar enthalpy ΔtrsHom = (14.67 ± 0.73) kJ·mol-1. The melting temperature of HCTD is 440 K, and the molar enthalpy of melting is ΔfusHom = (5.57 ± 0.28) kJ·mol-1. Standard molar thermodynamic functions of HCTD were calculated on the basis of these values at T = 298.15 K: Som (cr, 298.15 K) = (166.70 ± 0.70) J·K-1·mol-1, (ΔToHm/T)(cr, 298.15 K) = (84.46 ± 0.35) J·K-1·mol-1, Φom(cr. 298,15 K) = (82.25 ± 0.40) J·K-1·mol-1, and ΔToSom(g, 298.15 K) = (337.11 ± 5.53) J·K-1·mol-1. I.r. and Raman spectra of HCTD were recorded and vibrational analysis was made. The standard molar thermodynamic properties of HCTD in the gaseous state were calculated in the temperature range from 100 K to 1000 K. The calculated standard molar entropy at T = 298.15 K: Som(g) = 336.83 J·K-1·mol-1 is in good accordance with the experimental value. The thermodynamic results confirm indirectly the correctness of structural studies of HCTD made by Hargittai et al. © 1994 Academic Press Ltd.