Figure 7.

Expanded region of the ¹H NMR spectrum showing the diagnostic resonances of protons 17 and 21: (a) 100% Robusta sample, (b) 100% Arabica sample, and (c) 16-OMC standard. In the insets on the top of the figure, the signals of protons 17 and 21 of 16-OMC ester are enlarged. They are clearly visible in the Robusta sample (top), but they are absent from the Arabica sample. The arrow shows the weak methyl signals in position 21 of 16-OMC in its free form (Adapted with permission from [39]. Copyright 2014, American Chemical Society).