Radical Cations from the Reduction of Viologens

Bipyridinium salts are nearly colorless or pale yellow compounds that in solution can be very easily reduced to deeply colored radical cations. Although the 

The values of the hyperfine coupling constants are collected in Table 1. Because the hfs constants for aromatic protons are proportional to the spin densities at the adjacent carbon atoms through the McConnell relation,8 these values provide a clear-cut picture of the spin density distribution within the molecular framework of radical cation l+ The hfs constants for the nitrogen atoms should reflect, besides the spin density at the nitrogen atom itself, the spin density at the adjacent atoms as well as the nature of their bonds to the nitrogen.7 

Methyl viologen (2+ MV+ ), ethyl viologen (3+ EV+ ), and benzyl viologen (4+ , BV+ ) radical cations were obtained7 similarly to 1+ by photo- 

TaMc I. Hypertine Splitting Constants for Radical Cations 1 -4r  

The radical cations from several substituted A V -diphenyl viologens (PV) have also been investigated by means of EPR spectroscopy as well as electron nuclear double resonance (ENDOR) and triple resonance spectroscopies. 

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