Jk. Zhou et A. Rieker, ELECTROCHEMICAL AND SPECTROSCOPIC PROPERTIES OF A SERIES OF TERT-BUTYL-SUBSTITUTED PARA-EXTENDED QUINONES, Perkin transactions. 2, (5), 1997, pp. 931-938
Six extended para-quinones 1-6 with sterically hindered keto groups ha
ve been characterized by UV-VIS, H-1 NMR and C-13 NMR spectroscopy, Th
eir electrochemical properties were investigated in pyridine solution
using cyclic voltammetry, differential pulse voltammetry, chronoampero
metry and controlled-potential electrolysis, All species exhibit two s
uccessive one-electron reductions leading to the dianions via the mono
anions; the dianions can be reoxidized to the quinones, An EE-type mec
hanism for 1-6 was verified by computer simulation; the standard rate
constants (k(s1) and k(s2)) of the heterogeneous charge-transfer are i
n the region of 6.5-12.5 x 10(-3) cm s(-1). The first reduction peak p
otentials show a good linear relationship with the calculated LUMO ene
rgy levels, The radical anions, prepared electrochemically in the firs
t reduction step, were persistent for several hours in the absence of
air, They were also characterized by UV-VIS, EPR and ENDOR spectroscop
y revealing that the odd electron is delocalized over the whole pi-sys
tem.