DIRECTING EFFECTS OF PHENYL SUBSTITUTION IN THE REACTION OF OH RADICAL WITH AROMATICS - THE RADIOLYTIC HYDROXYLATION OF BIPHENYL

The initial yields for formation of 2-, 3- and 4-hydroxybiphenyl following the radiolytic oxidation of biphenyl in the presence of ferricyanide are, respectively, 2.19, 1.13 and 1.55 molecules/100 eV. These yields reflect relative rates of 0.71:0.37:1 for .OH radical attack on each of the ortho, meta, and para positions of biphenyl. Comparison of the corresponding partial rate constants to that for benzene shows that phenyl substitution has a significant effect in directing .OH addition to the ortho and para positions of aromatic systems. Comparison with phenol shows that a phenyl substituent has only a slightly smaller effect than does OH in increasing the partial rate constant at the ortho and para positions but is substantially less effective in decreasing the rate of .OH reaction at the meta position.