THE MOLECULAR-ORBITAL STUDIES ON HEATS OF FORMATION FOR NITRATES

The three SCF-MO methods of MINDO/3, MNDO and AMI were employed to calculate systematically the heats;df formation for 32 compounds of nitric acid esters at their optimized molecular geometries. Comparing with experimental values, the MNDO calculated results are much larger, and the MINDO/3 calculated results are better compared to available observed data in condensed phase. Owing to overcoming MNDO's shortcoming, which the repulsive van der waals energy among atoms was overestimated, the AM1 calculations get very satisfied results: there is good linear relationship between AM1 calculation results and observed data in gas phase for 7 title compounds; the linear correlation coefficient equals to 0.992. The average absolute difference and the average difference between them are only 10.28 and -1.01kJ/mol, respectively.