13CNMR Spectra of β-diketones from waxes of the gramineae

The ¹³CNMR spectra of six β-diketones and seven oxygenated β-diketones have been measured. The β-dicarbonyl grouping has the following effects on the chemical shifts of the neighbouring carbons: α-, + 8.72; β-, ? 3.98; γ-, ?0.42; δ-, ?0.33; ?-,?0.20; ζ-,?0.09; η-, ?0.05; θ-, ?0.03 ppm. The effects indicate the position of the grouping up to the 10,12-position. The positions of hydroxyl and oxo groups, up to the eighth carbon from the end of the chain, are also shown by long-range effects. The relative positions of a β-diketone grouping and another oxygen-containing group can be established from the ¹³CNMR spectrum with little ambiguity when they are separated by six or fewer methylene groups. For these structures NMR spectroscopy is more reliable than mass spectroscopy, which gives results which are difficult to interpret when groups are close together.Components of mixtures of hydroxy β-diketones, from grass waxes, are identified and proportions indicated by the NMR spectra.