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Conformational studies by nuclear magnetic resonance—III: ASIS and protonation studies of the rotational isomerism of enamino aldehydes and ketones
Author(s) -
Kozerski Lech,
Dąbrowski Janusz
Publication year - 1972
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270040207
Subject(s) - protonation , heteroatom , conformational isomerism , chemistry , steric effects , solvent , computational chemistry , photochemistry , ring (chemistry) , stereochemistry , molecule , organic chemistry , ion
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 α,β‐unsaturated ketones bearing no heteroatom, the Δδ 3, cis value but not the Δδ 3, trans , 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 C 2 .