 Solution

Product 6 is a remotely oxidized ketone of the undecylammonium chain, retaining the ammonium group and its counterion. Number from the ammonium-bearing carbon as C1. Crown-mediated recognition positions the remote C8–C9 region near the Mn–oxo center. A representative major-site product is the C8 ketone,Its adjacent possible regioisomer is the C9 ketone $[{\mathrm{H}}_3{\mathrm{N}}^{+}-(\mathrm{C}{\mathrm{H}}_2{)}_8-\mathrm{C}(\mathrm{O})-\mathrm{C}{\mathrm{H}}_2-\mathrm{C}{\mathrm{H}}_3]\mathrm{B}{\mathrm{F}}_4^{-}$. The precise single-site assignment is a limitation discussed below.

The crown ether binds the primary ammonium end through several N–H···O hydrogen bonds. This host–guest complex holds a folded portion of the chain close to the manganese oxidant, so the effective local concentration of a remote secondary C–H bond can overcome the intrinsic advantage of a free tertiary C–H bond. Such recognition-driven reversal of substrate preference is experimentally established.^[ref]

The key intermediates are the crown-bound ammonium–Mn=O assembly, a remote carbon radical after H abstraction, and the rebound secondary alcohol. A second oxidation removes the remaining hydrogen on the carbinol carbon to give the ketone. The overall oxygen-equivalent count isThus one ketone requires two equivalents of peroxide, explaining a maximum near 50% ketone yield with one equivalent and near-complete conversion with two.

The primary remote-oxidation study reports preference for C8 and C9, not a universally unique carbon. The schematic catalyst drawing and the oxygen budget alone cannot distinguish those positions quantitatively. The “single product” wording is therefore treated as an idealized remote-site assignment; a uniquely verified C8:C9 ratio is not invented.^[ref]