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Nitrogen-15 Nuclear Magnetic Resonance Spectroscopy. Solvent Effects on the ^(15)N Chemical Shifts of Saturated Amines and their Hydrochlorides

Duthaler, Rudolf O. and Roberts, John D. (1979) Nitrogen-15 Nuclear Magnetic Resonance Spectroscopy. Solvent Effects on the ^(15)N Chemical Shifts of Saturated Amines and their Hydrochlorides. Journal of Magnetic Resonance, 34 (1). pp. 129-139. ISSN 0022-2364. http://resolver.caltech.edu/CaltechAUTHORS:20151023-101624333

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Abstract

Solvent effects were determined for the^(15)N NMR chemical shifts of some primary, secondary, and tertiary amines along with solvent, concentration, and counterion dependences of the corresponding amine salts. The solvent effects on tertiary-amine nitrogen resonances appear to be dominated by hydrogen bonding to the lone pair, which results in downfield shifts. For primary and secondary amines, the situation is much more complex. Hydrogen bonding to the lone pair is apparently important, as indicated by a linear correlation of shifts produced by going from nonpolar solvents to methanol as solvent and shifts produced by protonation. The very large solvent and counterion effects sometimes observed for the ^(15)N chemical shifts of the conjugate acids of saturated amines seem best explained by ion-pair aggregation in relatively nonpolar solvents like chloroform, and especially with “soft” polarizable anions like iodide. Solvation of the salts in polar solvents or changes of anions expected to cause less ion aggregation result in upfield shifts of the nitrogen resonances, thereby decreasing the magnitude of generally downfield protonation shifts in nonpolar solvents. For some amines, this solvent effect may be so large as to cause protonation of a saturated amine to result in an upfield rather than the usually expected downfield shift.


Item Type:Article
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http://dx.doi.org/10.1016/0022-2364(79)90036-2DOIArticle
http://www.sciencedirect.com/science/article/pii/0022236479900362PublisherArticle
Additional Information:© 1979 Academic Press, Inc. Received May 27, 1978. Supported by the National Science Foundation, and by the Public Health Service, Research Grant No. GM-11072, from the Division of General Medical Sciences.
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U.S. Public Health Service (USPHS)GM-11072
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Caltech Gates and Crellin Laboratories of Chemistry5750
Record Number:CaltechAUTHORS:20151023-101624333
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20151023-101624333
Official Citation:Rudolf O. Duthaler, John D. Roberts, Nitrogen-15 nuclear magnetic resonance spectroscopy. Solvent effects on the15N chemical shifts of saturated amines and their hydrochlorides, Journal of Magnetic Resonance (1969), Volume 34, Issue 1, April 1979, Pages 129-139, ISSN 0022-2364, http://dx.doi.org/10.1016/0022-2364(79)90036-2. (http://www.sciencedirect.com/science/article/pii/0022236479900362)
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ID Code:61479
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:26 Oct 2015 21:31
Last Modified:26 Oct 2015 21:31

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