ELECTROCHEMICAL AND SPECTROSCOPIC PROPERTIES OF A SERIES OF TERT-BUTYL-SUBSTITUTED PARA-EXTENDED QUINONES

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.