Electron-Transfer Reactions with Participation of Ion-Radical Aggregates

2 Electron-Transfer Reactions with Participation of Ion-Radical Aggregates 

The disodium salt of diphenylacetylene dianion is stable in THE solution at -78°C. Methanol acts as a proton source toward the salt and causes the formation of a mixture of 1,2-diphenylethane with diphenylacetylene and small amounts of tran -stilbene (Chang and Johnson 1965, 1966). It seems logical that the reaction between (PhC=CPh) , 2Na and MeOH leads at first to PhCH=CHPh. The second step is supposed to consist of the further reduction of PhCH=CHPh at the expense of electrons from the nonreactedpartof the initial dianion. In principle, the electron transfer may proceed faster than the reaction of the initial dianion with protons. As a result, the diphenylacetylene dianion has to discharge into diphenylacetylene, whereas stilbene dianion has to form diphenylethane as follows  

one could predict that being mixed with methanol, the solution of PhCH=CHPh, (PhC CPh) , 2Na in THE might give PhCHjCHjPh and PhC CPh in quantitative yields. 

This obvious supposition occured to be false—the addition of stilbene causes no changes in the results of the reaction (Chang and Johnson 1965, 1966). It follows that an effective contact between PhCH=CHPh and (PhC=CPh) , 2Na is less than probable. As known, (PhC=CPh) , 2Na is a polymeric aggregate [(PhC=CPh) , 2Na+] . Bulk stilbene molecules are incapable of diffusing inside the aggregate. At the same time, the penetration of proton (or methanol) seems to be possible. 

it would be interesting to explore the behavior of acetylenic cation-radicals. Studies of negative Fukui functions for a family of substituted acetylenes showed that removing an electron from the HOMO induces electron rearrangement so that the electron density along the carbon-carbon bond increases. In other words, the electron density in one region of the molecule increases although the total number of electrons decreases (Melin et al. 2007). It must reflect in the reactivity of the acetylenic cation-radicals. 

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