Subsequent Literature and Varying Views
However, Birch did not accept this conclusion and continued publications suggesting meta protonation of the radical anion. He suggested the meta attack results from “opposition of the ortho and para initial charge”.
Bothner-By in 1959 had given qualitative arguments favoring meta-protonation as had been suggested previously by Birch.
Burnham in 1969 concluded that protonation is unlikely to occur predominantly at the ortho position and the reaction most probably occurs at the meta position but may occur at both sites at similar rates.
Subsequently, Birch in a review article noted that no experimental method at the time existed which would determine which was correct. But he did note that publication by Burnham favored meta attack.
In 1980 publications Birch collaborated with Leo Radom and considered ortho and meta densities to be close with a slight ortho preference but with mixtures of ortho and meta protonation occurring. RHF/sto-3g and UHF/sto-3g computations were used to conclude that both ortho and meta substitutions would occur with a slight preference for ortho.
Thus there had been a decade of controversy in the literature in which each of these two possible mechanisms was considered to be correct.
Read more about this topic: Birch Reduction
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