Evidence for hydrogen bond-like C–H–O interactions in aqueous 1,4-dioxane probed by high pressure
Resource
Chemical Physics Letters (397),205–210
Journal
Chemical Physics Letters (397),205–210
Pages
-
Date Issued
2004
Date
2004
Author(s)
Chang, Hai-Chou
Jiang, Jyh-Chiang
Chuang, Ching-Wei
Lin, Sheng-Hsien
DOI
246246/2006111501233044
Abstract
A series of substituted phenanthroquinones (PQ’s) was prepared, their phosphorescence spectra and decay rate constants, cyclic voltammograms,
and photoreaction in the presence of tetramethylethylene (TME) were investigated.With 450 nm irradiation their triplet excited
state cyclized with TME to give the corresponding dioxenes, 20,20,30,30-tetramethyl-10,40-dioxa-10,20,30,40-tetrahydrotriphenylene, cleanly
and much faster than that with 300 nm irradiation. The pattern of the reaction was effected weakly in random fashion by the substituent
at the 3-position of PQ’s. The photocycloaddition, as exemplified by PQ itself, is so efficient that it occurred even by room light and
during optical spectroscopic recordings; its limiting quantum yield in benzene is established to be unity with 450 nm irradiation. It owes
the unusual efficiency to a long lifetime of the PQ triplet excited state with the n–p configuration, and to the successful cyclization in
every diffusion controlled collision as implicated by TME quenching of PQ phosphorescence intensity in CCl4 solution. The triplet excited
state reaction was supported by competitive quenching of the dioxene formation by triplet quenchers as well as by oxygen. These PQ’s
do not fluoresce in solution, but show phosphorescence in solid solution with lifetimes of about 10 ms and in CCl4 solution with lifetimes
in the order of 100ms in the room temperature range. PQ’s with 3-cycano, 3-chloro, 3-methoxy, and without substitutions photocyclized
to cyclohexene to give the corresponding dioxenes with small stereochemical scrambles, that was interpreted that the extent of electron
transfer in the 1,6-diradical stage is small. Similar photocycloadditions to isobutene gave a 1:1 mixture of two regio-isomers, this was taken
as evidence for a direct radical attack on olefins to give 1,6-diradical intermediates.
Subjects
Excited state cycloaddition
o-Quinone triplet state reaction
Stepwise radical reaction
Stereo- and regio-specificity
Charge transfer contribution
Publisher
Taipei:National Taiwan University Dept Chem
Type
journal article
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