‘Through‐space’ hydrogen–fluorine, carbon‐fluorine and fluorine–fluorine spin–spin coupling in 2‐phenyl‐3‐alkyl‐4,5,6,7‐tetrahydroindazoles

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.