A reaction class approach with the integrated molecular orbital + molecular orbital methodology

We investigate the use of the reaction-class approach within the integrated molecular + molecular orbital (IMOMO) methodology for improving energetic information of chemical reactions. We have tested this approach using two classes of hydrogen abstraction reactions. One is abstraction from saturated hydrocarbons and the other from unsaturated hydrocarbons. For saturated hydrocarbon systems, this approach yields average unsign errors of the order of 1 kcal/mol in the reaction energy and about 0.2 kcal/mol in the barrier height. The errors are larger in the unsaturated hydrocarbon systems and are of the order of 2 kcal/mol. Analysis of the performance shows that this approach provides a practical and cost-effective tool for studying reactions involving large molecules.