A reaction class approach with the integrated molecular orbital plus 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 c lasses of hydrogen abstraction reactions. One is abstraction from saturated hydrocarbons and the other from unsaturated hydrocarbons. For saturated hy drocarbon 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 ar e of the order of 2 kcal/mol. Analysis of the performance shows that this a pproach provides a practical and cost-effective tool for studying reactions involving large molecules. (C) 1999 Elsevier Science B.V. All rights reser ved.