NMR Fluorine-Fluorine Coupling Constants in Saturated Organic Compounds

Abstract

The spectra of several fluorine-substituted, saturated, organic compounds have been investigated. It has been found that the coupling constants between 1,2 fluorine atoms are usually near zero. The coupling constants between 1,3 fluorine atoms in a free chain are usually between 7 and 10 cps if all of the intermediate skeletal atoms are carbon atoms. If one of the intermediate skeletal atoms is a nitrogen atom, these coupling constants go up to between 10 and 17 cps. The coupling constants between 1,4 fluorine atoms are usually in the range 2–7 cps when a nitrogen atom is in the intermediate skeletal chain. Rings usually reduce all coupling constants below the above stated values. Several exceptions are found to these generalizations. These generalizations with their exceptions lead the authors to believe that in the case of coupling between fluorine atoms, the main effect is not through-the-bonds, but rather a direct-through-space interaction. It is demonstrated that the restricted rotation about the carbon-carbon bonds has little to do with the near-zero coupling constants, but that these are readily explained on the basis of through-space coupling.

Concerning the origin of 19F19F NMR COSY and NOESY connections in the spectra of perfluorooctanoic acid, RF‐palmitic acid‐F13 and diethyl perfluorosuberate

“…In view of our interest in the 19 F NMR spectra of highly fluorinated compounds, in particular fatty acids, 18 we obtained 19 F- 19 F COSY, NOESY and 19 F spin-lattice relaxation times (T 1 ) for PFOA (1), R F -palmitic acid-F 13 (2) and diethyl perfluorosuberate (3). In an attempt to correlate our results with internuclear distances between fluorine atoms, we also carried out conformational minimization studies for these molecules using the semi-empirical AM1 approach.…”

2D 19F/19F NOESY for the assignment of NMR spectra of fluorochemicals

“…Although 19 F/ 19 F COSY experiments are routinely used for assignments in perfluorochemicals, assignment are often not obvious because four-bond ( 4 J FF ) coupling constants, typically 10 Hz, are much larger than the near zero vicinal ( 3 J FF ) coupling constants in linear CF 2 CF 2 groups. Throughspace fluorine-fluorine coupling is well known [10,11]. The large 25 Hz axial-axial 4 J FF in substituted perfluorocyclohexanes has been attributed to this mechanism [12] since 1,3-diaxial interactions determine the stereochemistry in six-membered rings [13].…”

Electron and Nuclear Spin Resonance

“…The following compounds have had their NMR spectra investigated : vinyl lithium (231) ; glycidaldehyde (232) ; tetramethyl cyclohexyl com pounds (233) ; cyclopentanone (234) ; CF3CF 2 CFICI (235) ; fluorine-satu rated compounds (236) ; vinyl chloride (237),; halogenated pro penes (238) ; 1,2,4-trichlorobenzene (239) ; pentafluorosulfur compounds (240) ; borazole (241) and borazole derivatives (242).…”