Effects of a hydroxyl substituent on the reactivity of the 2,4,6-tridehydropyridinium cation, an aromatic σ,σ,σ- triradical

摘要

The reactivity of 3-hydroxy-2,4,6-tridehydropyridinium cation was found to be drastically different from the reactivity of 2,4,6-tridehydropyridinium cation. While the latter triradical reacts with tetrahydrofuran, dimethyl disulfide and ally iodide via three consecutive atom or group abstractions, the former triradical exhibits this behavior only with tetrahydrofuran. Only a single atom or group abstraction was observed for the 3-hydroxy-2,4,6- tridehydropyridinium cation upon interaction with dimethyl disulfide and allyl iodide. This change in reactivity is caused by the hydroxyl group that strengthens the interactions between the two radical sites adjacent to it, thus reducing their reactivity. This explanation is supported by the observation of similar behavior for related biradicals. Gas-phase studies revealed that the introduction of the hydroxyl substituent to the 2,4,6-tridehydropyridinium cation (1) significantly influences its behavior toward neutral molecules. This is rationalized by the ability of the hydroxyl group to stabilize the cyclopropenium moiety of an ionic resonance structure, which results in a reduced dehydrocarbon atom separation for these two radical sites. The stronger coupling between these two radical sites drastically reduces their reactivity.