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Conformational studies on 2‐fluoro‐1,2‐disubstituted ethanes by NMR spectroscopy. Influence of electronegativity on vicinal proton–proton and fluorine–proton coupling constants
Author(s) -
Hamman Sylvain,
Béguin Claude,
Charlon Claude,
LuuDuc Cuong
Publication year - 1983
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/omr.1270210605
Subject(s) - electronegativity , vicinal , chemistry , proton , coupling constant , substituent , fluorine , hydrogen bond , chemical shift , crystallography , computational chemistry , stereochemistry , molecule , physics , organic chemistry , particle physics , quantum mechanics
The analysis of the ABKX spectra of thirteen compounds of the series RC(H‐K)(F‐X)C(H‐A)(H‐B)X gave the four vicinal proton‐proton and fluorine‐proton coupling constants. These coupling constants of conformationally mobile structures were used (i) to calculate the populations of the rotational states of the CHFCH 2 bond, (ii) to calculate the vicinal trans proton‐proton J (HH) t and gauche and trans fluorine‐proton coupling constants J (FH) g and J (FH) t and (iii) to give the unambiguous assignment of protons H‐A and H‐B. The dependence of the gauche and trans coupling constants with substituent electronegativity is explored. The results extend known correlations towards smaller electronegativity values. More quantitatively, the results and those in the literature, excluding those where deformations of torsional or bond angles occur, give a good fit of the data: a linear fit for J (HH) t = 15.0‐0.77 Σ(ΔE), an exponential fit for J (FH) g = 15.35 exp [‐0.266 Σ (ΔE)] and a linear fit for J (FH) t = 65.75 ‐ 7.52 Σ (ΔE), where Σ (ΔE) is the sum of the electronegativity difference between hydrogen and the six atoms or groups on the CHCF fragment.