Thermal Equilibrium Between Quinoid/Biradical Forms Enhancing Electrochemical Amphotericity.
Chemistry
; 30(35): e202400916, 2024 Jun 20.
Article
em En
| MEDLINE
| ID: mdl-38644537
ABSTRACT
Upon dibenzo annulation on Thiele's hydrocarbon (tetraphenyl-p-quinodimethane), the quinoid form and the biradical form adopt quite different geometries, and thus are no longer resonance structures. When these two forms can interconvert rapidly due to the small energy barrier (ΔG≠), the equilibrated mixture contains both forms in a ratio that is determined by the energy difference (ΔGo) between the two forms. For a series of tetrakis[5-(4-methoxyphenyl)-2-thienyl]-substituted derivatives, the more stable quinoid form and the metastable biradical form coexist in solution as an equilibrated mixture due to small ΔG≠ (<15â
kcal mol-1) and ΔGo (1-4â
kcal mol-1), in which the proportion of the two forms can be regulated by temperature. Since the biradical form can undergo easy two-electron (2e) oxidation to the corresponding dications as well as easy 2e-reduction to the dianions, it exhibits very high electrochemical amphotericity. This character with a record-small span for not only the first oxidation and reduction potentials but also the second those, [E1 sum≈E2 sum=E2 ox-E2 red=ca. 1.4â
V], is attained through thermally enhanced conversion to the biradical form from the corresponding quinoid form, the latter of which is less amphoteric due to higher Eox and lower Ered values.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Idioma:
En
Revista:
Chemistry
Assunto da revista:
QUIMICA
Ano de publicação:
2024
Tipo de documento:
Article
País de afiliação:
Japão
País de publicação:
ALEMANHA
/
ALEMANIA
/
DE
/
DEUSTCHLAND
/
GERMANY