Computed vibrational spectra of candidate structures were obtained by performing quantumchemical calculations using the Gaussian 16 software package. Input structures for the computations were generated using an automated workflow for conformational searching that uses the SMILES structure format of the neutral molecule as input. Details of this computational workflow are described elsewhere. In short, using the cheminformatics toolbox RDkit , the workflow generates protonation isomers considering all nucleophilic sites of the neutral molecule and performs a conformation search for each isomer using a distance geometry algorithm. The resulting conformers (500) are minimized using the MMFF94 force field. The minimized structures are clustered based on similarity, resulting in a maximum of 10 conformers. These are minimized at the PM6 level of theory and structures with a relative energy (with respect to the lowest-energy conformer) of <40 kJ/mol are further optimized at the B3LYP/6-31++G(d,p) level of theory. For structures with relative energies below 20 kJ/mol, a (likely) more accurate energy value was obtained from a single-point MP2/6-311++G(2d,2p) calculation using the B3LYP optimized geometry; these values were used in the final energy ranking. Harmonic vibrational frequencies were calculated at the B3LYP/6-31++G(d,p) level. Frequencies were scaled by 0.975 and broadened with a Gaussian line shape of 20 cm -1 full width at half maximum to facilitate easy comparison with experimental spectra.