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Ionization Shifts in 1H-NMR Spectra of α,β-Unsaturated Carboxylic Acids

✍ Scribed by Jerzy W. Jaroszewski; Peter Grossen; Peter Mohr; Christoph Tamm

Publisher
John Wiley and Sons
Year
1986
Tongue
German
Weight
480 KB
Volume
69
Category
Article
ISSN
0018-019X

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✦ Synopsis

Changes in chemical shifts of olefinic protons in a number of a$-and a,P,y,G-unsaturated carboxylic acids caused by ionization of the COOH group were investigated. The ionization shifts of a-H-atoms are -0.09 to 0.07 ppm, those ofg-H-atoms are 0.324.47 ppm. The ionization shifts of 8-H-atoms are substantially larger than those of y-H-atoms. The ionization shifts can be used for immediate determination of the esterification site in monoesters of (2E,4Z)-2,4-hexadienedioic (muconic) acid, which are of interest in connection with synthetic studies on verrucarins. Thus, isomerization by heating in aqueous solution of monoesters of (2Z,4Z)-2,4-hexadienedioic acid yields 1-monoesters rather than 6-monoesters of (2E,4Z)-2,4-hexadienedioic acid, in accordance with the isomeriration mechanism involving anchimeric assistance of the free COOH group. Solutions of the ABXY spectra of olefinic protons of monomethyl (2E,4E)-and (2Z,4Z)-2,4-hexadienedioate are reported.

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