The structure of and interactions in binary acetonitrile + water mixtures

Binary liquid mixtures of acetonitrile (AN) and water (W) are widely used as reaction media in such fields of chemistry as physical organic chemistry, reverse phase liquid chromatography, and electrochemistry, among others. Much information on the structure of these systems and the interactions in them has accumulated since the author's often quoted comprehensive 1990 paper, so that a review is merited. Macroscopic physical properties, results from diffraction and spectroscopic studies, theoretical considerations and computer simulations, and results from the use of solute probes all bear on the structure (and less so on the dynamics) of the mixtures. These are discussed in terms of the microheterogeneity that occurs in them at intermediate contents (that leads eventually to liquid-liquid phase separation).