Theoretical studies on heats of formation for cubylnitrates using density functional theory B3LYP method and semiempirical MO methods

The heats of formation (HOF) have, been calculated for all the 21 cubylnitrate compounds using the semiemprical molecular orbital (MO) methods (MINDO/3, MNDO, AM1, and PM3) and for 8 of 21 cubylnitrates containing 1-4-ONO2 groups using the density functional theory (DFT) method at the B3LYP/6-31G* level by means of designed isodesmic reactions-The cubane cage skeletons in cubylnitrate molecules have been kept in setting up isodesmic reactions to produce more accurate and reliable results. It is found that there are good linear relationships between the HOFs of the 8 cubylnitrates calculated using B3LYP/6-31G* and two semiempirical MO (PM3 and AM1) methods, and the linear correlation coefficients of PM3 and AM methods are 0.9901 and 0.9826, respectively. Subsequently, the accurate HOFs at B3LYP/6-31G* level of other 13 cubylnitrates containing 4-8-ONO2 groups are obtained by systematically correcting their PM3-calculated HOFs. Compared with noncaged nitrates, all the 21 cubylnitrates have high heats of formation implying that they may be very powerful energetic materials and have highly exploitable value. The relationship between the HOFs and the molecular structures of cubylnitrates has been discussed. (C) 2002 John Wiley & Sons, Inc.