2) are carried out in progressively more dilute mixtures of HBA (hydrogen bond acceptor) solvents in non-HBA cosolvents. VF50 values of Me2S0 (volume fractions of MezSO in the cosolvents at which the hydrogen bonded complex with 1 is approximately half dissociated) are shown to increase in magnitude with increasing polarity of the cosolvent. A linear relationship between log VFbO values for the Me2SO:1:Me2S0 complex and formation constants reported earlier for the 4-fluorophen01:Me~SO hydrogen bonded complex in the same cosolvents is demonstrated. Self-associating alcohol solvents show nontypical dilution behavior. Dissociation of the (ROH), complexes simultaneously with the l:(ROH), complexes causes -AAv( 1-2) values (enhanced bathochromic shifts attributable to hydrogen bonding) to fall off more rapidly on dilution into non-HBA cosolvents. A comparison of dilution behavior provides strong evidence that the (MeOH), self-association equilibrium constant is significantly higher than that for (t-BuOH),.