The most thorough, recent, and/or relevant studies are those ofĮaton, Pena-Nuñez, and Symons,1 Ben-Amotz, Lee, Cho, and Number of studies of this effect have been performed. Obtained in 33 solvents (including the neat liquid), and a large Revealing data set, the change in frequency, ∆ν, of the CN Indeed, a vast amount of experimental data for ACN in Of these observations, a physical picture for the solvation of
Of a unified model which could quantitatively account for all Pyridine (Py), suggests that subtle structural effects are also very Our analysis, presented herein, of spectroscopic dataįor dilute ACN in the notionally noncomplexing solventĬhloroform (CHCl3), as well as the strongly basic solvent † Current address: Molecular Electronics Research, 393 Darling St., While very dilute ACN in MeOH is at least 20% uncomplexed MeOH in ACN known to exist in tetramer or larger clusters, (MeOH) and ACN also show similar effects,7,8 with very dilute
Known to form a thin layer at the liquid-air interface aboveĪqueous solutions ordered akin to the surface of neat acetonitrile,6 and here we present spectroscopic evidence for two types Further, from the work of Eisenthal et al.,5 ACN is Solution is thought to separate into regions of ACN and regions Has led to the postulate of microheterogeneity,2-4 in which the Mixtures exhibit anomalous thermodynamic properties, and this Liquids containing ACN are very complex.1 Water-ACN Is, however, becoming evident that the structural properties of Many hydrophobic and hydrophilic materials will dissolve. Suggest that microheterogeneity could also account for most known properties of acetonitrile-alcohol solutionsĪnd, in fact, be a quite general phenomenon.Īcetonitrile (ACN), both when neat and when mixed with,Į.g., water (HOH), is a very commonly used solvent in which Although such theories are still in their infancy, we Theories for the structure of acetonitrile-water solutions.
Raman spectroscopy and show that the results are consistent with, but require modification of, microheterogeneity Also, we measure ∆ν for acetonitrile in aqueous solution using Fourier transform Known structural properties of the various solutions and/or related neat liquids, leading to an interpretation of Well as 45 parallel calculations for the solvent monomers or dimers. Shifts for CH3CN complexed with one molecule of either water, methanol, ethanol, 2-propanol, tert-butylĪlcohol, phenol, benzyl alcohol, acetic acid, trifluoroacetic acid, 2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoro2-propanol, acetonitrile, chloroform, carbon tetrachloride, tetrahydrofuran, formamide, pyridine, or Cl-, as Specific solvation, 95 MP2 or B3LYP calculations are performed to evaluate structures and CN frequency In terms of solvent repulsive and dielectric effects combined with specific solvation effects. Solvent-solute forces compete to determine the structure of the solution and hence ∆ν. WeĪscertain the robust features of these models and combine them into a new one in which solvent-solvent and Have been proposed to interpret ∆ν are based on diverse experiments with incompatible conclusions. The two major models (dispersive and specific solvation) which Shift, ∆ν, of its CN stretch frequency, ν2. Properties of acetonitrile dissolved in 33 solvents, focusing on interpretation of the environment-sensitive solvent Of the nature of mixed liquids containing acetonitrile applicable across-solvent families. ReVised Manuscript ReceiVed February 18, 1999Ībstract: Acetonitrile is an extremely important solvent and cosolvent. Contribution from the School of Chemistry, UniVersity of Sydney, NSW 2006, Australia
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