Experimental and Theoretical-Study of Carbon-Fluorine Couplings in the NMR-Spectra of 2-Fluoroaryl Ketones

Abstract

Calculations by the IPPP-INDO method give the spin-spin coupling constants for the side-chain carbons, 3JCF and 4JCF, as 4.97 and 6.86 Hz respectively with substantial contributions to through-space coupling from the pathway CO-C-H…F. The observed values for 1-(2- fluorophenyl ) ethanone , 3.3 and 7.2 Hz, and for 1-(2,5- difluorophenyl ) ethanone , 3.7 and 7.3 Hz, are in good agreement with these predictions. Two compounds, a dihydroindenone and a naphthalenone, in which this pathway cannot be effective, show no fluorine coupling to the aliphatic carbon next to the carbonyl and the values of 3JCF are reduced to 2.2 and 2.5 Hz, consistent with the loss of a through-space Fermi contact term of the kind described above.

Analysis of 19F and 13C NMR spectra of tetrafluorophthalic anhydride and its derivatives

“…The data obtained from double resonance experiments show that 4 J C-1,F-6 has the largest absolute value equal to 4.1 Hz for 4 and 4.4 Hz for 5, while both 3 J C-1,F-7 and 4 J C-1,F-4 values do not exceed 2 Hz. These results are consistent with 3 J C-1,F-7 = 2.0 Hz and 4 J C-1,F-4 = 1.6 Hz values observed in the spectrum of 4,7-difluoro-3-methylindan-1-one [25]. The values of 4 J C-1,F-6 and 5 J C-3,F-6 calculated for compounds 4 and 5 are close to those determined experimentally (see Table 2).…”

Through-space 13C–19F coupling can reveal conformations of modified BODIPY dyes†

“…As part of our investigations to determine molecular structure we observed that a through-space 13 C-19 F coupling 10 is observed only for compounds 1a, 1b and 2a in this series, and this parameter can be correlated with their molecular conformation. These compounds show a triplet in their 13 C{ 1 H} spectra (1a d 130.1, t, J = 11.0 Hz; 1b d 128.4, t, J = 11.2; 2a d = 126.7, t, J = 5.2 Hz). APT and HETCOR experiments 11 established that the carbons responsible for these triplets were the ones marked a (henceforth referred to as C a ).…”

Conformational analysis. Part 29.1 The conformational analysis of 2-substituted fluoro- and trifluoromethyl-benzaldehydes, acetophenones and methyl benzoates by the lanthanide induced shift (LIS) technique

“…The solutions were made up as 0.5  in deuteriochloroform which had been stored for at least 24 h over molecular sieves prior to use. The shift reagent Yb(fod) 3 is available commercially and Lu(fod) 3 was prepared following Springer et al 19 The shift reagents were dried in vacuo over P 2 O 5 at ca. 35 ЊC for 24 h, and maintained in vacuo over P 2 O 5 between successive additions to the sample.…”

“…These molecules can exist in the O-cis and O-trans forms (Scheme 1) and the relative energy of the two forms is a sensitive measure of the F ؒ ؒ ؒ O᎐ ᎐ C and F ؒ ؒ ؒ R interactions. Furthermore, as the interactions of the fluorine substituent are of a major significance in the conformational analysis and the fluorine nucleus is also an excellent NMR-active nucleus it was also of interest to determine whether the 19 F LIS could be used with the same degree of certainty in the analysis as the 1 H and 13 C LIS.…”