Problems that may be encountered in the application of solvent basicity characteristics in estimation of solute interactions are considered. A model of interactions of acid solutes with basic solvents through hydrogen bonding was developed and confirmed by experimental data on the solvent effect on O-H stretching vibration of phenol. The properties of the associates formed between acid solutes and basic solvents are differently affected by nonspecific interactions with the solvent and this is probably the source proper of problems in evaluation of medium effects.