Hydrogen-atom abstractions: a semi-empirical approach to reaction energetics, bond lengths and bond-orders

We propose the use of the Intersecting-State Model (ISM) to estimate activation barriers and reactive bond distances for reactions involving the transfer of hydrogen atoms. The method is used in at variety of systems with transition states of the (H)C-H-C(H), N-H-C(H), O-H-C(H), S-H-C(H), Si-H-C, Si-H-Si, Sn-II-C and Ge H-C types. Hydrogen abstractions by halogen atoms are also investigated. Results are compared with available experimental, semi-empirical or ab initio data. Other transition state types (such as O-H-O) which cannot be properly rationalized in the light of an elementary bond-breaking/bond-forming process are also analyzed.