FURTHER EVIDENCE FOR THE RADICAL-CHAIN CHARACTER OF GRIGNARDS REAGENTFORMATION - USE OF FREE-RADICAL CLOCK IN CONJUNCTION WITH CHANGES IN CONCENTRATION OF ACTIVE MG

The reaction of endo-5-(2'-haloethyl)-2-norbomene (X=I, Br, Cl) with a ctive Mg obtained by metal vaporization yields both cyclized and uncyc lized organomagnesium compounds. The ratio cyclized / uncyclized incre ases in the order Cl < Br < I. This ratio decreases when the ratio Mg / RX increases suggesting that the radicals formed by E.T. from Mg to RX may be trapped by Mg at a rate competitive with the rate of cycliza tion of a norbornenyl radical.