2,2,3,3-Tetramethylbutane: Heat Capacity, Heats of Transition, Fusion and Sublimation, Vapor Pressure, Entropy and Thermodynamic Functions

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The heat capacity of solid 2,2,3,3-tetramethylbutane was studied between 12/sup 0/K, and the melting point, 373.97 +- 0.05/sup 0/K. The transition temperature (152.5 +- 0.2/sup 0/K), heat of transition (478 cal./mole/sup -1/), and heat of fusion (1802 cal./mole/sup -0/) were determined. The entropy of the solid at 298.16/sup 0/K was found to be 65.43 +- 0.15 cal./deg/sup -1//mole/sup -1/. The vapor pressure was measured from 0 to 65/sup 0/ and the following equation was selected to represent the data: log/sub 10/p = 7.92864 - 1709.428/(t + 233.634). The heat of sublimation calculated from the vapor pressure data is 10.365 +- 50 cal./mole/sup -1/. The standard entropy of the vapor at 298.16/sup 0/K was found to be 93.05 +- 0.30 cal./deg/sup -1//mole/sup -1/. By utilizing the results of relatively detailed normal coordinate calculations as a guide in interpreting the spectra, a vibrational assignment adequate for purposes of thermodynamic computations was obtained. The average height of the potential barriers hindering internal rotation that is required to give agreement with the observed value of the entropy is 4700 cal./mole/sup -1/. Using this value of the average barrier height, the vibrational assignment, and other pertinent molecular-structure data, the thermodynamic functions -(F/sup 0/ - H/supmore » 0//sub 0/)/T, H/sup 0/ - H/sub 0//sup 0/, S/sup 0/, and C/sup 0//sub p/ for 2,2,3,3-tetramethylbutane were computed for selected temperatures up to 1500/sup 0/K.« less