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Conformational studies by nuclear magnetic resonance—III: ASIS and protonation studies of the rotational isomerism of enamino aldehydes and ketones

✍ Scribed by Lech Kozerski; Janusz Dąbrowski

Publisher
John Wiley and Sons
Year
1972
Tongue
English
Weight
323 KB
Volume
4
Category
Article
ISSN
0749-1581

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✦ Synopsis

The s-cis + s-trans equilibrium of several enamino ketones and aldehydes, has been evaluated based on the results of aromatic solvent induced shift measurements and of protonation of the title compounds. In contrast to cc,p-unsaturated ketones bearing no heteroatom, the A&,,,, value but not the A.83,t7.n8, proved to be useful in conformational assignments. Protonation, which occurs mainly on oxygen, enhances the rotational barrier, thus enabling the observation of both rotamers at room temperature. Steric hindrance to conjugation enhances the rate of protonation at the carbon C2. I N T R O D U C T I O N * For Part 11, see Ref. Ic.

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