Visible absorption spectrum of benzophenone radical anion in dipolar aprotic solvents

Two-parameter regression including the acceptor number (AN) and permittivit y (epsilon) of the solvent explains to some extent the solvatochromic shift of the absorption band of benzophenone radical anion (Ph-2(C)over dot-O-) in the visible region. In 11 dipolar aprotic solvents characterized by epsi lon > 10, in which the Ph-2(C)over dot-O- anions are not associated with (C 2H5)(4)N+ cations (the radicals were prepared by cathodic reduction of benz ophenone in the presence of (C2H5)(4)N+CLO4- as electrolyte) a correlation equation has the form v(max) (in cm(-1)) = 86.2(AN) - 19.7 . 10(3)[(epsilon - 1)/(2 epsilon + 1)] + 21.32 . 10(3). It reflects the relative stabilizat ion of the ground state in a medium with a high acceptor number and an incr ease in the dipole moment of Ph-2(C)over dot-O- during excitation.