The effect of meta- and para-methoxy substitution on the reactivity of the radical cations of arylalkenes and alkanes. Radical ions in photochemistry. Part 26

The effect of meta- and para-methoxy substitution on the reactivity of some radical cations has been determined. The compounds chosen for study were 1-(3-methoxyphenyl)-1-phenylethylene ( 7 ), 1-(4-methoxyphenyl)-1-phenylethylene ( 8 ), 3-(3-methoxyphenyl)indene ( 9 ), 3-(4-methoxyphenyl)indene ( 10 ), methyl 2-(3-methoxyphenyl)-2-phenylethyl ether ( 11 ), methyl 2-(4-methoxyphenyl)-2-phenylethyl ether ( 12 ), cis- and trans-2-methoxy-1-(3-methoxyphenyl)indane ( 13 ), and cis- and trans-2-methoxy-1-(4-methoxyphenyl)indane ( 14 ). The radical cations of these compounds were generated by photosensitization (electron transfer) using 1,4-dicyanobenzene ( 3 ) as the electron acceptor. The three reactions studied were: (1) The addition of nucleophiles (methanol) to the radical cation of the arylalkenes, a reaction that yields the anti-Markovnikov addition product. (2) The carbon-carbon bond cleavage of radical cations, which yields products derived from the radical and carbocation fragments. (3) The deprotonation of the radical cation, a reaction that can be used to invert the configuration at a saturated carbon centre. The mechanisms of these reactions are discussed and the factors that need to be considered in order to predict reactivity are defined. Molecular orbital calculations (UHF/STO-3G) were carried out on the radical cations of the model compounds 3- and 4-vinylanisole and 3- and 4-methylanisole. Key words: photochemistry, photosensitize (electron transfer), radical cation, radical.