Quaternary Spectra Research Articles

Analyses of Carbon-13 Nuclear Magnetic Resonance Spectra of Isopropyldibenzofurans and Their Structural Determinations

Carbon-13 NMR spectra of isomers of four mono- and three diisopropyldibenzofurans were recorded by an NMR spectrometer with a magnet of 9.4T (or 400MHz type). Even if the sample was a mixture of components or was of only 50% purity, unequivocal assignments were obtained by means of carbon-proton correlated spectroscopy (C-H COSY). Based on the α-effect by isopropyl group, and with the assistance of quaternary spectra (QUAT), one of diisopropyldibenzofurans was determined to be 2, 4-isomer, and not 1, 3-isomer which can not be ruled out by 1H NMR. The chemical shifts of the isopropyl groups are more dependent on substituent positions in 13C than in 1H NMR spectra. All 36 possible kinds of isopropyldibenzofurans are distinguishable using the present results together with 1H NMR data.