Addition of selenium atoms to double and triple bonds

8 ADDITION OF SELENIUM ATOMS TO DOUBLE AND TRIPLE BONDS 

By analogy with sulphur atoms, the addition of triplet selenium atoms to olefins would be expected. Callear and Tyerman [123—125] investigated the photolysis of CSe2—olefin mixtures in the mid-1960 s and their results are given in Table 32. There does not seem to have been any work reported since then. 

The selenium atoms produced by the CSe2 photolysis were moderated with nitrogen gas. The rates of the reactions were generally determined by measuring the rate of formation of C—Se bonds, which gave new absorption bands in the ultraviolet. The compounds studied show the approximate reactivities one would expect if the reaction of selenium 

There are some obvious discrepancies, or, at least oddities, in this series that need explanation. These include the fairly low reactivity of propene with selenium atoms, and the wide divergence of rates for the cis- and frans-2-butenes. The high rate for the (rons-2-butene seems to be a consequence of the low activation energy, but this is, of course, not an explanation. The addition of tellurium atoms, described in the next section, shows the expected large difference in reactivity between ethylene and propene, which indicates the selenium value is probably not correct, but unfortunately the list of olefins investigated is severely limited and does not include the cis- and frans-2-butenes. 

Relative rates for sulphur and selenium atom additions to olefins  

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