Naphthalene and Azulene I: Semimicro Bomb Calorimetry and Quantum Mechanical Calculations

Carl Salter

Department of Chemistry, Moravian College, Bethlehem, PA 18018

James B. Foresman

Physical Sciences Department, York College of Pennsylvania, York, PA 17405

Abstract

A novel H2O? physical chemistry experiment is proposed in which the heats of combustion of naphthalene and azulene are measured using bomb calorimetry, and then the energy difference between the two molecules is computed using Gaussian 94W. Azulene is an expensive hydrocarbon ($100/gram); semimicro bomb calorimetry using the Parr 1425 makes the experiment possible using just 0.1 grams of azulene. The experimental difference obtained by students using this apparatus was -34 kcal/mole (azulene - naphthalene); the literature value is -32 kcal/mole. Using the B3LYP? /6-31G(D)//RHF/6-31G(D) level of theory we compute an energy difference of -32 kcal/mole; the literature value for the gas-phase energy difference between azulene and naphthalene is -35±2 kcal/mole. Thus this experiment demonstrates that excellent agreement can be obtained between experiment and modern methods of computational chemistry.

Journal of Chemical Education, 1998, 75, 1341                       Full text (PDF)

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