‘Through-space’ hydrogen–fluorine, carbon-fluorine and fluorine–fluorine spin–spin coupling in 2-phenyl-3-alkyl-4,5,6,7-tetrahydroindazoles
✍ Scribed by John W. Lyga; Robert N. Henrie II; Gary A. Meier; R. William Creekmore; Russell M. Patera
- Publisher
- John Wiley and Sons
- Year
- 1993
- Tongue
- English
- Weight
- 526 KB
- Volume
- 31
- Category
- Article
- ISSN
- 0749-1581
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✦ Synopsis
Abstract
^1^H, ^13^C and ^19^F NMR experiments for a series of 3‐alkyl‐2‐phenyl‐4,5,6,7‐tetrahydroindazoles revealed a six‐bond through‐space coupling between the ortho‐fluorine and the hydrogen or fluorine atom of the position 3‐alkyl group. This was further supported by NOE experiments. Molecular mechanics calculations on a representative structure indicated that several low energy conformers met the fluorine‐carbon distance constraint suggested by the NMR data, and dynamic annealing experiments produced a conformer which was in complete agreement with the NMR data. This through‐space interaction is speculated to be a result of repulsion between N‐1 of the tetrahydroindazole and the ortho‐fluorine lone pair electrons.