This experiment was utilized to determine the vapor pressures and enthalpies of sublimation for vanillin and o-vanillin. The experiment used a diffusion pump with a liquid nitrogen trap to expose pellets of vanillin and o-vanillin to low pressures at specified temperatures. Geometry optimizations were performed on the monomers and π-stack, mirror and rotated mirror dimer structures of vanillin and o-vanillin using the semi-empirical AM1 level of theory. The computational results gave energies of -91.64 kcal/mol and -89.73 kcal/mol for vanillin and o-vanillin respectively. The results from the dimer structures of vanillin gave values of -183.42 kcal/mol for the π-stack, -183.12 kcal/mol for the mirror and -187.69 kcal/mol for the rotated mirror structures. . The results from the dimer structures of o-vanillin gave values of -181.42 kcal/mol for the π-stack, -182.24 kcal/mol for the mirror and -182.06 kcal/mol for the rotated mirror structures. The results suggest that the rotated mirror structure was the most stable structure for the vanillin and the mirror structure was the most stable structure for the o-vanillin.
The vapor pressures for vanillin for trials 1 and 2 were found to be 0.24 Pa (75 °C) and 0.064 Pa (60 °C) respectively, and 0.034 Pa (38 °C) and 5.36E-3 Pa (31 °C) for trials 1 and 2 for o-vanillin. The experimental enthalpies of sublimation for vanillin and o-vanillin were found to be 82.6 kJ/mol and 180.7 kJ/mol respectively. The literature values were found to be 88.7 kJ/mol for vanillin and 54.1 kJ/mol for o-vanillin. The experimental and literature values for vanillin are fairly close while the values for o-vanillin differ by a larger magnitude. The experimental results suggest that o-vanillin is more stable than vanillin, but this is not true. An error must have arisen in the experiment that skewed the data for the o-vanillin data such as water trapped in the crevices of the Knudsen cell. It is suggested that the experiment be performed with improved equipment and a more water tight cell be used.
That class sounds terrible. Half the words in your first sentence were over my head, so I figure half the concepts in the class are things that I wouldn't understand.
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