Premium
Solvent‐Induced Deuterium Isotope Effects in 13 C‐ and 15 N‐NMR. Spectra of Enaminones
Author(s) -
Kozerski Lech,
von Philipsborn Wolfgang
Publication year - 1982
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19820650715
Subject(s) - chemistry , protonation , kinetic isotope effect , deuterium , isotopomers , chemical shift , nmr spectra database , isotope , solvent , resonance (particle physics) , nuclear magnetic resonance spectroscopy , proton , analytical chemistry (journal) , crystallography , spectral line , molecule , stereochemistry , organic chemistry , ion , physics , astronomy , particle physics , quantum mechanics
The effect of deuterium on the 13 C and 15 N chemical shifts of enaminones has been investigated. D/H isotope shifts are reported for neutral and protonated species, i.e. , when the isotope is exchanged on the C(2)‐, N‐, or O‐atoms. In cases of slow exchange the isotope shifts were obtained from solutions containing both isotopomers, whereas for fast exchange (acidic solutions) either separate NMR. sample tubes ( 15 N‐NMR.) or coaxial tubes ( 13 C‐NMR.) were used. In neutral molecules the isotope effects δ C (D, H) are intrinsic in nature. In acidic solutions, the enaminocarbonyl cations formed exhibit δ C (D, H)‐ and δ N (D, H)‐values which are discussed in terms of the proton transfer. The mesomeric character of the cations is reflected by characteristic features in the δ C (D, H)‐ and δ N (D, H)‐values, which can be ascribed to isotopic perturbation of resonance. O ‐Protonation shifts in the 15 N‐resonance, observed for the first time, are large and positive (+60 to +76 ppm), in contrast to amides, where the effects are of the same sign but an order of magnitude smaller. Both protonation shifts and solvent‐induced isotope effects are discussed in connection with the nucleophilic character of the reactive centers in the enaminone synthon.