6533b7d9fe1ef96bd126d4e3

RESEARCH PRODUCT

1H,13C,17O and19F NMR spectroscopic study of isomeric ring-substituted monofluoro-(E)-3-phenylpropenals

subject

description

Isomeric ring substituted monofluoro-(E)-3-phenylpropenals (cinnamaldehydes) were synthesized in order to provide, with the NMR-active 19F nucleus, an insight into the influence of substituents and the transmission of electronic effects between the aromatic ring and the side-chain. Their 1H, 13C and 17O NMR chemical shifts and their nJ(H,H), nJ(H,F), nJ(C,H) and nJ(C,F) values were determined. Generally, the nJ(C,F) coupling constants correlate with the length of the coupling route and thus simplify the assignments of the 13C NMR spectra. Only the side-chain carbons C-2 and C-3 in the ortho-substituted compounds showed an exception to this rule. Many long-range nJ(H,F) (n = 4–7) values were easily observed. The 17O NMR chemical shift of the carbonyl oxygen in the o- and m-fluoro derivatives show clear substituent effects, whereas p-fluorocinnamaldehyde shows a value comparable to that of that parent compound.