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Polarity‐Dependent Isomerization of an Unsymmetrical Overcrowded Ethylene Promoted by Zwitterionic Contribution in the Twisted Isomer
Author(s) -
Hirao Yasukazu,
Nagamachi Nobuhiro,
Hosoi Katsuma,
Kubo Takashi
Publication year - 2018
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201701805
Subject(s) - isomerization , chemistry , solvent polarity , metastability , solvent , photochemistry , polarity (international relations) , double bond , polar , crystallography , polymer chemistry , organic chemistry , catalysis , biochemistry , physics , astronomy , cell
The twisted form of bianthrone is known as a metastable state provided by a photo‐induced or thermal‐induced isomerization of the folded form, and thus prevents the isolation and the detailed analysis of its electronic structure. In this study, an unsymmetrical bianthrone ( 2 ), consisting of the electron‐withdrawing anthrone and electron‐donating acridane, have been synthesized and shown to exhibit a solvent‐polarity‐dependent isomerization reaction between the folded and twisted isomers. With increasing the polarity of the solvent, 2 showed an isomerization reaction from the folded form to the twisted form. The stabilization of the twisted isomer in polar solvents can be interpreted as proof of its relatively large zwitterionic character. The DMF solution of 2 displayed paramagnetically‐broadened NMR signals from the thermally populated triplet state resulting from rotation of the weakened ethylenic double bond of the twisted isomer.