TOPOLOGICALLY CONTROLLED COULOMBIC INTERACTIONS, A NEW TOOL IN THE DEVELOPING OF NOVEL REACTIVITY - PHOTOCHEMICAL AND ELECTROCHEMICAL CLEAVAGE OF PHENYL ALKYL ETHERS

The hypothesis that a specific placement of a positive charge would dr amatically alter the behavior of a charged intermediate has been teste d. Phenyl ethers substituted by electron-attracting groups do not unde rgo reductive fragmentation. However, related a-piperidino-omega-(4-su bstituted-phenoxy)-alkanes give alkyl ether photocleavage when the lin ker between the redox centers is short, or the usual substitution-redu ction photochemistry when it is long. Mechanistic experiments suggest that the photofragmentation process operates through space intramolecu lar electron transfer to the triplet aromatic chromophore and that a c oplanar relative orientation of the alkyl ether bond and the phenyl ri ng is compulsory for the photofragmentation to be observed. Configurat ion interaction AM1 calculations justify the described facts, indicati ng that the fragmentation process is only operative when a Coulombic s tabilization of a sigma intramolecular electron transfer excited stat e is produced. Electrochemical studies carried out with the correspond ing quaternary salts (intermolecular generation of the phenyl ether ra dical anion) confirm the conclusions derived from the photochemical ex periments.