Endothermic processes bond breakage

The reaction Oz —> 20 is an endothermic reaction since it requires the breaking of the bond between two oxygen atoms without the formation of any bonds. Since bond breakage is endothermic, the entire process must be endothermic. 

B. Cross Section Measurements In recent years crossed molecular beam techniques have been employed by Lee and co-workers ( ) to study extensively Ihe reactions of fluorine atoms with several different olefins. Very high cross-sections were observed, consistent with the rapid thermal rate constants measured above. In these ejqieriments, multichannel decomposition is observed (i. e., loss of H or CH3 after F addition to the ff -bond). Since the C-F bond is stronger dian any other single bond with a carbon atom, C-F bond scission teck to the original reactants does not compete with the exothermic processes involving breakage of C-C and C-H bonds. A tabulation of AH values for addition reactions of thermal F to various olefins is included (Table II) ( ). Some hi ly endothermic pathways are listed for the purposes of comparison. The ei eri-mental measurements of D/S in this table confirm that the only radicals undergoing appreciable C-C bond rupture with carbene formation after thermal F addition are those that form CF2. The extraordinary stability of the CF2 radical makes C-C bond rupture exothermic for these radicals. 

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