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1997
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Research: Science and Education
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Useful Examples for Discussion of Proton-NMR Spectroscopy: N-Substituted alpha-Aminobenzenebutanenitriles-Anisotropy of Diastereotopic Methylene Protons
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John Almy, R. Martinez Alverez, A. Herrera Fernandez, and A. Sanchez Vazquez
Universidad Complutense, Departamento de Química Orgánica I, Facultad de Ciencias Químicas, E-28040 Madrid
SPAIN
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December 1997
Vol. 74 No. 12
p. 1479
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| Abstract |
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Undergraduate texts commonly discuss the anisochrony (non-coincidence of NMR signals) of methylene protons near chiral center using projections in which the chiral center and the carbon bearing the methylene protons are separated by a single bond. An analysis of the various rotational conformers about this bond demonstrate the non equality of the protons in question and reinforces the fact that the chemical shift for a given proton is the weighted average for the proton in its various conformations. N-substituted derivatives of the alpha-aminobenzenebutanenitrile system and alpha-methyaminopropanenitrile are obtained by easy one step syntheses. During the characterization of these compounds, which have two consecutive methylene groups attached to their chiral center, we were surprised to observe that although both pairs of methylene protons are diastereotopic and therefore anisochronous, only the gamma protons actually displayed different chemical shifts. The ß protons, which are separated from the chiral center by fewer bonds, gave no measurable chemical shift difference. The degree of anisochrony is not always a function of the distance from a chiral center and will vary with the solvent used in the analysis. We report here a summary of the study we made to explore this phenomenon.
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| More Information |
 Citation |
Almy, John; Martinez Alverez, R.; Fernandez, A. Herrera; Vazquez, A. Sanchez. J. Chem. Educ. 1997 74 1479.
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Keywords |
NMR Spectrometry, Organic Chemistry, Analytical Chemistry, and Instrumental Methods
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History |
Created:
Last Updated: |
July 20, 1999
June 23, 2005
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| Home > JCE Print > Journal of Chemical Education > Issues >
1997
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December
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1479
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