Direct Structure Determination of the Self-Condensation Product of 1-Phenylpentane-2,4-dione Using T1 and NOE Measurements from 13C NMR Spectroscopy

Article abstract of DOI:10.1002/omr.1270211209

The nuclear Overhauser effect (NOE) is known to depend on molecular dynamics and structure.However, in some cases the values obtained for selective homonuclear and heteronuclear NOE are much too small, considering that the nuclei involved are located within a short distance of each other in space.A quantitative treatment of the NOE values alllows a clear explanation of this apparent anomaly, and allows the possibility of using T₁ and NOE values measured with broad-band proton irradiation.The corresponding relationship is useful for solving many structural problems in organic chemistry, and has the great advantage of employing the typical high resolution of fully decoupled spectra.The method was used in this work for the structure determination of teh self-condensation product of 1-phenylpentane-2,4-dione, and it was concluded tha the previous assignment of the 13C NMR spectrum was erroneous.An independent proof of the new assignment is given using the selective collapse of the fine structure under low-power irradiation of the methyl protons.