Oleic acid
Auto-oxidation of oleic acid was reported previously . “Clean” observation of a methine carbon bonded to oxygen (-CHO-) drove us to communicate the discovery, Figure 8 . 13C NMR reveals on average, 40% of the starting carboxylic acid carbons are converted into esters (Table 1 ). Two olefinic carbons and one carboxylic carbon are lost per acyl chain. In correspondence, a major species with one ester per methine bound to oxygen (CHO-) forms (T1 below). Previously, a dimer was suggested. But, to satisfy overall oxidation, addition of oxygen to both olefinic carbons (C9,10) is required. Otherwise, with only one ester bond (mono-acylation), net oxidation does not occur (Figure S13 ).