Addition of chlorine atoms to double and triple bonds

3 ADDITION OF CHLORINE ATOMS TO DOUBLE AND TRIPLE BONDS 

Goldfinger, Dainton, Knox and their collaborators have been principally involved in the elucidation of chlorine atom additions to olefins. This reaction is one of the most elegantly worked out of any of the atom additions. The work with the chlorinated ethylenes has been especially painstaking. It would be pleasant to be able to report that there is universal agreement in the experimental results as a consequence, but the rates vary considerably. One thing which is completely accepted, however, is that the chlorine atom—ethylene initial adduct is formed in an excited state, viz. 

The kinetic studies of chlorine atom additions to simple olefins have not covered a very wide range of structures. This is largely because Cl readily abstracts allylic hydrogens, and this complicates the stoichiometric, and therefore the rate, picture. Results are summarized in Table 12. 

The accepted mechanism (for ethylene, as an example) is given below. I ermination is probably by cross combination [51]. In this mechanism RH is a reference hydrocarbon such as ethane or propane, chosen so that the rate of addition can be related directly to the known rate coefficient of hydrogen abstraction. 

The value of log k = 10.65 for ethylene in Table 12 is probably closest to the correct value because it is calculated from the competitive rate for hydrogen abstraction which is now fairly well established [52], and 

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