Infrared (C—N stretch) and n.m.r (13^C,14^N) methods have been used to probe the solvation of MeCN molecules and CN– ions in water,methanol and a range of mixed protic-aprotic media. For MeCN,the i.r. results are unusual in that protic solvents induce a high-frequency shift in νmax(CN),whereas dipolar aprotic solvents give a low-frequency shift. The interpretation given of this is that both σ- and π-electron interactions play an important role in hydrogen-bond formation,whereas π interactions are dominant for dipolar solvents such as Me2SO. The 13^C(CN) shifts are too small to give useful information,but the 14^N shifts correlate well with the i.r. results. It is argued that in methanolic solution MeCN forms only one hydrogen bond and that ca. 50% of the molecules are not hydrogen bonded. In water,all MeCN molecules are hydrogen bonded. The results do not distinguish between mono- and di-bonding,but other evidence suggests that di-bonding is likely to occur. Similar experiments on CN– ions show again that protic solvents induce a high-frequency shift. Mixed-solvent studies suggest that at least four methanol or water molecules are normally hydrogen bonded to the ions; this is in accord with other spectroscopic results on the same solvents. The experiments have been complemented by a series of molecular dynamics simulations on dilute solutions of MeCN and CN– in water and methanol. The predicted solvation numbers from the simulations are in good agreement with those derived from the experimental data,particularly for MeCN. There are some discrepancies for CN–,but these may in part be attributable to difficulties involved in finding an acceptable definition of solvation number in cases where this quantity is large.
|Data di pubblicazione:||1988|
|Titolo:||Spectroscopic and molecular dynamics studies of solvation of cyanomethane and cyanide ions|
|Autore/i:||Graham, Eaton; Anthony S., Pena Nuñez; Martyn C. R., Symons; Ferrario, Mauro; Ian R., Mcdonald|
|Digital Object Identifier (DOI):||10.1039/DC9888500237|
|Serie:||FARADAY DISCUSSIONS OF THE CHEMICAL SOCIETY|
|Titolo del libro:||FARADAY DISCUSSIONS OF THE CHEMICAL SOCIETY|
|Citazione:||Spectroscopic and molecular dynamics studies of solvation of cyanomethane and cyanide ions / Graham, Eaton; Anthony S., Pena Nuñez; Martyn C. R., Symons; Ferrario, Mauro; Ian R., Mcdonald. - STAMPA. - 85(1988), pp. 237-253.|
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