Abstraction of Atoms and Radicals

Consider as an example the reaction of atomic hydrogen with molecular propane. The following four reaction paths are possible 

Two of these reaction paths (1 and 2) belong to the first group (atom abstraction) and the other two (3 and 4) to the second group of exchange reactions. 

The absence of reliable data on reactions (3) and (4) supports the assumption of their low probability compared to reactions (1) and (2). 

The low probability of radical abstraction might be accounted for by the complicated structure of the transition complex and its more substantial rearrangement. 

Consider now the alkyl radical disproportionation reactions. In these reactions the attacking radical abstracts a hydrogen atom from the radical attacked to form an alkane molecule and an olefin molecule. If the disproportionation involves two different radicals, two reaction paths are possible  

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