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Effects of protonation and hydrogen bonding on carbon-13 chemical shifts of compounds containing the >C=N:− group

Allen, Malwina and Roberts, John D. (1981) Effects of protonation and hydrogen bonding on carbon-13 chemical shifts of compounds containing the >C=N:− group. Canadian Journal of Chemistry, 59 (2). pp. 451-458. ISSN 0008-4042. doi:10.1139/v81-065.

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The effects of hydrogen bonding and protonation produced by changing solvent from chloroform to 2,2,2-trifluoroethanol to trifluoroacetic acid were determined for the 13C chemical shifts of fourteen imines, four oximes, and two pyridines. Downfield shifts relative to chloroform were observed for the C=N carbon of the imines and oximes in both trifluoroethanol and trifluoroacetic acid, ranging from 1.5 to 27.5 ppm, which contrasts with upfield Cα shifts for the pyridines in trifluoroacetic acid. Substantial downfield and upfield shifts of from +10 to −15 ppm were found for the para and ipso carbons, respectively, of the aromatic rings attached to the C=N group in trifluoroacetic acid. Possible explanations of these shift changes are considered as well as their relation to the corresponding changes in 15N shifts with the identical variations in solvent.

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Additional Information:© 1981 NRC Canada. Received March 4, 1980. This paper is dedicated to Prof. Raymond U. Lemieux on the occasion of his 60th birthday. Supported by the National Science Foundation, and by the Public Health Service, Research Grant No. GM-11072 from the Division of General Medical Sciences. Gates and Crellin Laboratories of Chemistry, Contribution No. 6180.
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Public Health ServiceGM-11072
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Gates and Crellin Laboratories of Chemistry6180
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ID Code:11214
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Deposited On:24 Jul 2008 17:57
Last Modified:08 Nov 2021 21:34

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