Walden inversion single

The abstraction process proceeds by homolysis and is kinetically of the first-order (SNl-like). It involves two steps formation of new radicals, via the homolytic cleavage of the nonpolar, perfectly covalent bond in H2, in absence of any electrophile or nucleophile to initiate the heterolytic pattern, and the subsequent recombination of a new radical with another radical species. The hydride exchange is an example of the kinetically second-order, the first-order in both the incoming (nucleophile) and leaving (nucleofuge) hydride groups. It proceeds via the familiar Walden-inversion Transition State (TS) in a single, concerted reaction. 

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