Low Temperature Calorimetric Studies of Seven 1- Olefins: Effect of Orientation Disorder in the Solid State

Abstract

From low temperature calorimetric measurements, values of the heat capacities in the solid and liquid states and of the heats and temperatures of phase changes were obtained for the following compounds: 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene and 1-hexadecene. Values of the entropy and other thermodynamic properties of each compound were calculated at selected temperatures in the range 10 to 360/sup 0/K. The thermal behavior of this series of 1-olefin hydrocarbons is more complex than that of the corresponding series of n-paraffins. By comparing the entropy values of 1-olefins with those of the n-paraffins, it was found that 1-undecene, 1-dodecene and 1-hexadecene crystallize in a state of orientational disorder. In 1-hexadecene crystals, virtually complete end-for-end disorder occurs. Because 1-undecene and higher 1-olefins do not form perfect crystals, the Third Law cannot be used to calculate absolute entropy values from the experimental data for these three compounds. However, the results reported here and elsewhere for the C/sub 5/ to C/sub 10/ hydrocarbons, inclusive, show that the entropy of these 1-olefins in the liquid state at 298.16/sup 0/K is 0.19 +- 0.02 cal./deg./sup -1//mole/sup -1/ less than that of the corresponding n-paraffins. Thus, reliable values of the entropy of the higher 1-olefinsmore » may be calculated by subtracting 0.19 cal./deg./sup -1//mole/sup 1/ from the entropy value of the corresponding n-paraffin. The experimental and calculated entropy values of the 1-olefin hydrocarbons from 1-octene to 1-hexadecene are represented within 0.04 percent by the equation, S/sub satd./ (liq., 298.16/sup 0/K) = 24.349 + 7.725 N cal./deg./sup -1//mole/sup -1/, where N is the number of carbon atoms in the molecule.« less