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

Abstract

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.