P122
A New Aspect of The "Meta-Effect" on Methoxybenzyl Acetate Photolysis in Methanol
Makoto Nomachi,
Ken Fujimori
University of Tsukuba
Zimmerman explained much greater photosolvolysis product yield for meta-methoxybenzyl acetate
(30%) in 50% aqueous dioxane than that for the para-isomer (2%) in terms of better electron
transmission of methoxy-substituent to the meta-position to pronounce the "meta effectt".
Meanwhile, Pincock explained the phenomenon by the mechanism that whole photo-excited
methoxybenzyl esters undergo C-O bond homolysis to form singlet methoxybenzyl/acetoxyl
radical pair and the solvolysis product yield is determined by rate ratio of an electron
transfer to form methoxybenzyl acetate ion pair vs a sum of acetoxyl decarboxylation
and diffusion rates of the initial singlet radical pair. We report here that
the photolytic C-O bond scission of meta-methoxybenzyl acetate occurs from singlet excited state
but that of para-methoxybenzyl acetate occurs from triplet excited state in methano1.
Our results are different from that reported by the above two researchers and shed light
on the "meta-effect", an recent attractive subject in photochemistry.
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