0 Phenylpropionate (Fatty acid with odd number of carbon atoms) Franz Knoop's labeling Experiments (1904) C +C2 Benzoate fatty acids are degraded by oxidation at theβ carbon, 1. e, B oxidation Phenylbutyrate Fatty acid with even number of carbon atoms) CH2-C、+C2 Phenylacetate a  a Franz Knoop’s labeling Experiments (1904): fatty acids are degraded by oxidation at the  carbon, i.e.,  oxidation