ORGN 926 |
| Concentration dependent chemical shift changes of non-exchangable hydrogens of a variety of heterocyclic aromatic compounds result in dramatic 1H-NMR spectral pattern changes, sometimes so pronounced, that they can lead to 1D and 2D spectral signatures that may be misleading. We have proposed that this may be due π-π interaction between the molecules. We continue our investigations on the role and nature of π-π interaction in concentration dependent chemical shift changes with substituted indoles and indole containing natural products, like reserpine (1) and isoreserpine. The spectral patterns of simple substituted indoles at different concentrations vary remarkably, and in some cases result in cross over or coalescence of signals. The 1H-NMR spectra of reserpine, which contains the indole moiety, shows concentration dependent chemical shifts in the aromatic and, surprisingly, in the aliphatic regions, resulting in cross over of signals. We propose, from NOESY experiments with reserpine, isoreserpine and the methyl reserpates, that it is π-π interaction between the indole rings that cause the concentration dependent chemical shift changes.
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Heterocycles and Aromatics
1:00 PM-4:40 PM, Thursday, 14 September 2006 Moscone Center -- Room 135, Oral
Division of Organic Chemistry |
