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K. Jackowski, P. Bernatowicz, E. Wielogórska

Intermolecular Interactions of Aliphatic Nitriles in Aprotic Solvents Studied by ¹³C and ¹⁴N NMR Chemical Shifts

¹³C and ¹⁴N NMR chemical shifts of the cyano group have been observed for the solutions of four aliphatic nitriles (i.e. acetonitrile, propionitrile, isovaleronitrile and pivalonitrile) in ten aprotic solvents. It is shown that both the NMR chemical shifts are very sensitive on intermolecular interactions. The nitrogen shielding is increased and the carbon shielding is decreased when self-associate structures of nitriles are partially destroyed upon dilution in aprotic solvents. Ab initio GIAO-CHF calculations suggest that the solvent-solute dimers already exhibit the changes of nuclear magnetic shielding which are apparently seen in the ¹³C and ¹⁴N NMR spectra of investigated solutions. A correlation between the ¹⁴N and ¹³C dilution effects is observed for acetonitrile and propionitrile. It is explained by the presence of strong self-association structures of solute molecules. The two other aliphatic nitriles (isovaleronitrile and pivalonitrile) still give similar variations of nitrogen and carbon shielding upon dilution but the correlation between their carbon and nitrogen chemical shifts is not observed. It proves that the self-associates of nitriles are weaker as the volume of an aliphatic substituent is increased.

Zeitschrift für Physikalische Chemie, Oldenbourg Wissenschaftsverlag

Print ISSN: 0942-9352
Volume: 216, 12/2002
Pages: 1401

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