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Configuration of cross‐conjugated caroten‐20‐als: 2D NMR study on four isomers of renierapurpurin‐20‐al
Author(s) -
Englert Gerhard,
Glinz Ernst,
LiaaenJensen Synnøve
Publication year - 1988
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260260114
Subject(s) - chemistry , conjugated system , spectral line , cis–trans isomerism , chemical shift , nuclear overhauser effect , proton , two dimensional nuclear magnetic resonance spectroscopy , nuclear magnetic resonance spectroscopy , nmr spectra database , spectroscopy , stereochemistry , proton nmr , crystallography , pulse sequence , nuclear magnetic resonance , organic chemistry , physics , quantum mechanics , astronomy , polymer
The 400 MHz 1 H NMR spectra of four cis isomers of synthetic renierapurpurin‐20‐al (χ,χ‐caroten‐20‐al) were completely assigned by application of two‐dimensional proton‐proton chemical shift correlated spectroscopy (2D COSY) with high digital resolution of ca 0.4 Hz per point by acquisition of only the olefinic part of the spectra. Connectivities to the methyl and aldehyde protons absorbing outside the measured range were also obtained owing to the folding of their cross‐peaks along the F 1 axis. Nuclear Overhauser difference experiments and consideration of chemical shift changes were applied to derive unequivocally the 13‐ cis (13 E ), 7,13‐di‐ cis (7 Z ), 13,7′‐di‐ cis (7′ Z ) and 13,9′‐di‐ cis (9′ Z ) configuration of the isomers. The 1 H‐detected one‐bond 1 J (CH) and long‐range 2,3 J (CH) multiple quantum coherence heterocorrelated 2D spectra of 1.2 mg of the main 13‐ cis isomer were acquired and the 13 C signals partly assigned. The structural consequences with respect to other cross‐conjugated caroten‐20‐als are discussed.