Transition state geometry in radical hydrogen atom abstraction

The data on quantum chemical calculations of interatomic distances in the transition state of the radical reactions of hydrogen atom abstraction, X^•+HY → XH+Y^•, are generalized and described systematically. Depending on the reaction centre structure, these reactions are subdivided into classes with the X...Y interatomic distance being the same within each class. Data on the transition state geometry obtained by the methods of intersecting parabolas and intersecting Morse curves are presented. The reaction centre X...H...Y is shown to be almost linear, the hydrogen atom position in it being determined by the reaction enthalpy. The effects of triplet repulsion, electronegativities and radii of the atoms X and Y, the presence of π-bonds adjoining the reaction centre and steric effects on the X...Y interatomic distance is analyzed and characterized. Bibliography — 62 references.