Figure shows the IR spectrum of [DOPAC-H] -along with the three best matching spectra in the in silico library and their corresponding structures (see results for all 16 isomers in Figure ). The computed spectrum of [DOPAC-H] -indeed yields the highest spectral similarity. Interestingly, metabolites that are structurally similar to DOPAC give the second and third highest scores, 3,4dihydroxymandelaldehyde and 3,5-dihydroxyphenylacetic acid, respectively. These metabolites are the only 1,2-positional isomers of DOPAC in the set of 16 isomers (Figure ) and have the highest structural similarity with DOPAC (0.56 and 0.78).