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A crown ether with fifteen ring atoms, including five oxygen donor atoms.

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]

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.

The two terminal alkenes undergo olefin metathesis. Their terminal methylene groups combine to give U = ethene, $\mathrm{C}{\mathrm{H}}_2=\mathrm{C}{\mathrm{H}}_2$. Connecting the two internal alkene carbons of the same molecule gives Z, the unsaturated crown ether macrocycle. Following the drawn chain gives four oxygens, six carbons in the three internal ethylene links, two O-adjacent methylenes at the ends and two alkene carbons: a 14-membered ring containing four oxygens.

The ring connectivity is specified completely by the cyclic sequenceThe final methylene reconnects to the first alkene carbon. The examination does not fix alkene stereochemistry, so a single E/Z assignment is not required.

At high concentration, intermolecular encounters compete strongly with ring closure, giving Y, an unsaturated polyether formed by acyclic diene metathesis polymerization. Its repeat connectivity can be writtenFor a finite linear chain, terminal groups depend on conversion and work-up; its internal repeat is the relevant structural answer. Reduced pressure removes ethene and promotes metathesis conversion, while dilution reduces bimolecular chain growth relative to intramolecular closure. These competing routes are documented by the original authors' chemical study.^[ref]