SIDE-CHAIN HYDROXYLATION OF AROMATIC-COMPOUNDS BY FUNGI .4. INFLUENCE OF THE PARA-SUBSTITUENT ON KINETIC ISOTOPE EFFECTS DURING BENZYLIC HYDROXYLATION BY MORTIERELLA-ISABELLINA

The benzylic hydroxylation of a series of para-substituted toluenes by the fungus Mortierella isabellina has been studied by using CD3, CHD 2, and CH2D methyl labelled substrates. Inter- and intramolecular primary and secondary deuterium kinetic isotope effect ratios have been determined: the intermolecular primary effects are maximal with strongly electron-withdrawing para substituents (R = CN and CF3), while the intramolecular primary effects are minimal for R = H but increase in instances where R is electron donating or withdrawing. These results are interpreted in terms of a dependence of the hydroxylation mechanism on the nature of the para substituent.