Certain physical and chemical properties of energetic aliphatic and aromatic compounds can be used to predict their usefulness as explosives. Computational chemistry and molecular-modeling procedures may be applied to predict some of these same properties. We describe experiments suited for the undergraduate instructional laboratory in which the heats of formation of several compounds are calculated using semiempirical procedures. Three semiempirical models, AM1, MNDO, and PM3, were evaluated. In general PM3 proved most successful in its ability to predict the heats of formation of the energetic compounds studied when compared, to experimental data. Cubane was an exception. The calculated heat of formation (474.97 kJ/mol) of this highly strained aliphatic compound was substantially less than the experimentally determined (622.2 kJ/mol) value. Semiempirical (PM3) calculations for octanitrocubane, a new high explosive, predicted a heat of formation of 552.7 kJ/mol. This value is within the rather broad range (339-728 kJ/ mol) calculated by others using a variety of procedures. However, it is substantially less than presumably more accurate values calculated using an isodesmic approach Coupled with density functional theory.
|Original language||English (US)|
|Number of pages||4|
|Journal||Journal of Chemical Education|
|State||Published - Feb 1 2007|