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Structural studies by 1 H and 13 C dynamic n.m.r.: Part III alternative protonation sites in carbonyl conjugated enamines of the type R 1 C(O)CHCHNR 2 R 3
Author(s) -
Kozerski Lech
Publication year - 1977
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.1270090705
Subject(s) - protonation , pyridinium , chemistry , trifluoroacetic acid , chemical shift , medicinal chemistry , ion , stereochemistry , crystallography , organic chemistry
13 C magnetic resonance spectra of several enamino ketones with secondary and tertiary amino groups were obtained for trifluoroacetic acid solutions. In both series O ‐protonation is predominant and the chemical shifts are related to the electron density changes with respect to the parent base. The spectra of the tertiary compounds are interpreted in terms of slow rotation around the C–1C–2 and C–3N bonds discernible at room temperature. O ‐protonated forms of the secondary enamino ketones undergo further reaction on C–2 yielding pyridinium salts. The mechanism of formation of the quaternary salts is interpreted and the additivity parameters of the 13 C n.m.r. chemical shifts in the pyridinium ions is briefly discussed.