Past exam of the chemistry course of the year 4 of the natural sciences course of the University of Cambridge / 2022 / Paper 1 / 14 / c / Solution

Ba${}^{2+}$ competes strongly for the crown ether receptors. With the recognition sites occupied, the undecylammonium chain can no longer be effectively preorganized near manganese. The reaction should move back towards oxidation of methylcyclohexane to 1-methylcyclohexan-1-ol, with suppression of the selectively formed remote amino ketone.

The single available peroxide equivalent is then sufficient for tertiary C–H hydroxylation, whereas a secondary-chain ketone would require two oxidations. Competitive binding constants and metal-induced structural changes would determine the exact conversion and residual selectivity; neither a numerical yield nor complete inhibition of all oxidation follows merely from adding two equivalents of barium salt.