Proton, carbon-13 and fluorine-19 NMR studies of N-alkyl-8-fluoroquinolinium halides: Relative signs of through-space 1H19F and 13C19F coupling constants

✍ Scribed by M. Barfield; S. R. Walter; K. A. Clark; G. W. Gribble; K. W. Haden; W. J. Kelly; C. S. Le Houllier

• Publisher: John Wiley and Sons
• Year: 1982
• Tongue: English
• Weight: 851 KB
• Volume: 20
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1270200206

✦ Synopsis

Abstract

Because of experimental and theoretical interest in long‐range ^1^H^19^F and ^13^C^19^F coupling constants between proximate atoms, a series of N‐alkylfluoroquinolinium compounds was synthesized and the NMR parameters were accurately measured. By means of spin tickling and selective population inversion difference spectroscopy, the ^5^J(HF) and ^4^J(CF), which are associated with the proximate fluorine and methyl groups, were shown to be of the same (positive) sign as the directly bonded ^13^C^1^H and vicinal ^1^H^1^H coupling constants. In N‐methyl‐8‐fluoroquinolinium iodide (1a) and chloride (1b) ^5^J(HF)=+8.8 and ^4^J(CF)=+16.3 Hz, and in N‐ethyl‐8‐fluoroquinolinium iodide ^5^J(HF)=+3.0, ^6^J(HF)=+1.5, ^4^J(CF)=(+)15.8 and ^5^J(CF)=±5.2 Hz. Calculated molecular orbital results, which were based on the INDO‐FPT method and a molecular geometry from the x‐ray diffraction data for 1b, were in reasonable agreement with the ^4^J(CF) values, but the ^5^J(HF) values were of the wrong sign and magnitude.