Characterization of Phenolic Plant Exudates by Nuclear Magnetic Resonance Spectroscopy

The class of plant exudates that contain the phenol functionality, termed phenolics, is defined, surveyed, and characterized by solid-state C-13 NMR spectroscopy and by solution-state H-1 NMR spectroscopy. Materials in this group are identified by the phenolic C-13 resonance (from the ipso carbon of ArOH) at delta 145-160 (delta 160-167 for ArOR). The resonance patterns define several subclasses based on the collective similarity of their C-13 spectra, specifically, aloetics from the genus Aloe, guaiacs from the genus Guaiacum and other eurosid and conifer genera, xanthics from the genus Garcinia, and kinos from the genus Eucalyptus and many other genera. Phenolic exudates often are mixed with terpenoid materials (the building block of exudates known as resins) and carbohydrates (the building block of exudates known as gums) to form hybrid subgroups such as guaiac gums, guaiac resins, and kino resins. There are numerous phenolic exudates not affiliated with any of these groups, both as pure phenolics and as hybrids (phenolic resins, phenolic gum resins, and phenolic waxes).