1H, 13C and 19F NMR spectroscopy of polyfluorinated ureas.: Correlations involving NMR chemical shifts and electronic substituent effects

Seventeen N-(mono-, di-, tri-, tetra- and penta-fluorophenyl)-N'-(3-nitrophenyl)ureas were prepared and characterized. Complete assignment of their H-1, C-13 and F-19 NMR data was undertaken and the correlation of the chemical shifts of the ureido protons with field-inductive and mesomeric electronic substituent parameters was studied using the Swain-Lupton model. The best correlations were obtained when the study was limited to certain substitution patterns, e.g. non-ortho, mono-ortho- and di-ortho-fluorinated ureas, which reveal probable changes in conformations caused by the degree of ortho fluorination at the phenyl ring. Additionally, there is an excellent linear cross-correlation between the chemical shifts of the fluorine atoms and the ipso carbon atoms for the whole group of fluorinated ureas. Copyright (c) 2005 John Wiley & Sons, Ltd.