. Can. J. Chem. 69,839 (1991). The effect of mera-and para-methoxy substitution on the reactivity of some radical cations has been determined. The compounds chosen for study were 1-(3-methoxypheny1)-1-phenylethylene (7), 1-(4-methoxypheny1)-1-phenylethylene (S), 3-(3-methoxypheny1)indene (9), 3-(4-methoxypheny1)indene (lo), methyl 2-(3-methoxypheny1)-2-phenylethyl ether ( l l ) , methyl 2-(4-methoxypheny1)-2-phenylethyl ether (l2), cis-and trans-2-methoxy-1-(3-methoxypheny1)indane (13), and cis-and trat1s-2-methoxy-l-(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 (UHFISTO-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 DONALD R. ARNOLD, XINYAO DU et KERSTIN M. HENSELEIT. Can. J. Chem. 69,839 (1991). On a dttermint l'effet de substituants en me' ta et en para sur la rCactivitC de quelques radicaux cations. Les composCs choisis pour cette ttude sont : les 1-(3-mtthoxyphtny1)-1-phtnylCthyl&ne (7), 1 -(4-mCthoxyphtny1)-1 -phtnyltthylkne (S), 3-(3-mtthoxyphtny1)indkne (9), 3-(4-mtthoxyphtnyl)ind&ne (lo), 1-mtthoxy-2-(3-mtthoxyphtny1)-2-phCnyltthane ( l l ) , I-mtthoxy-2-(4-mCthoxyphtny1-2-phtnyltthane (12), les cis-et trans-2-mtthoxy-I-(3-mtthoxyphtny1)indane (13) et les cis-et trans-2-mtthoxy-1-(4-mtthoxyphtny1)indane (14). On a gCnCrC les cations radicaux de ces composts par photosensibilisation (transfert d'Clectron), en utilisant le 1,4-dicyanobenzkne (3) comme accepteur d'tlectrons. Les trois rtactions ttudites sont: (1) l'addition de nuclCophiles (methanol) aux cations radicaux des arylalcknes, une rtaction qui conduit ?I un produit d'addition anti-Markovnikov; (2) le clivage de la liaison carbone-carbone des cations radicaux qui conduit ?I des produits qui dtrivent des fragments radicalaires et carbocationiques et (3) la dtprotonation des cations radicaux qui peut Ctre utiliste pour inverser la configuration ?I un site carbon6 saturt. On discute des mCcanismes de ces rkactions et on dtfinit les facteurs qu'il faut considtrer afin de pouvoir prtdire la rtactivitC. On a effectut des calculs d'orbitales moltculaires (UHF/ STO-3G) sur les cations radicaux des composts modkles, 3-et 4-vinylanisole et 3-et 4-mtthylanisole.

Radical Ions in Photochemistry. Part 26. The Effect of meta-and para-Methoxy Substitution on the Reactivity of the Radical Cations of Arylalkenes and Alkanes.-The radical cations (8 examples) are generated by irradiation in methanol/acetonitrile in the presence of 1,4dicyanobenzene as electron acceptor. Three reactions are studied: the addition of nucleophiles (methanol) to the radical cation which yields anti-Markovnikov products, further the carbon-carbon bond cleavage of the radical cations which affords products derived from radical and carbocation fragments and, finally, the deprotonation of the radical cations (mechanisms).-(ARNOLD, D. R.; DU, X.; HENSELEIT, K. M.; Can. J. Chem. 69 (1991) 5, 839-852; Dep. Chem., Dalhousie Univ., Halifax, Nova Scotia, Can. B3H 4J3; EN)