Supporting information for the entitled contribution. It contains: Static quantum chemical and high accuracy molecular dynamics computational data on protomers, tautomers, zwitterions, and isotopomers of caffeine (CAFF), paraxanthine (PARAXAN), theobromine (THEOBR), theophylline (THEOPH), and guanine (GUA), uric acid (UA), and xantine (XAN), as well as their derivatives. The content includes data on characteristic parent and product ions of the analytes in ion mobility spectrometric and mass spectrometric experimental conditions. Tautomers, charge transfer processes, and intramolecular rearrangement; if any, are accounted for considering. Molecular mechanics/molecular dynamics data are shown as *.txt files. High accuracy molecular dynamics includes adiabatic computations using Born-Oppenheimer approach. High accuracy static ground state and transition state computations use M062X/SDD level of theory. Figures in color, illustrating the entitled contribution shown as *.pdf files. The experimental ion mobility spectrometry and mass spectrometry data are according to reference [1]. [1] H. Sepman, A. Kruve, S. Tshepelevitsh, H. Hupatz, Experimental IMS and MS/MS data of caffeine metabolites (2022). Zenodo, [https://doi.org/10.5281/zenodo.6637393][ https://zenodo.org/record/6637393] (Accessible for 04.04.2022.) They have been used and processed via the following software: [2] ProteoWizard 3.0.11565.0 (2017) [https://proteowizard.sourceforge.io/download.html]; [3] mMass 5.0.0 [http://www.mmass.org/download/old.php]; [4] AMDIS 2.71 (2012) software [https://chemdata.nist.gov/mass-spc/amdis/downloads/AMDIS_Installer-17.zip]; and [5] NIST Search Software 2.0 [https://chemdata.nist.gov/dokuwiki/lib/exe/fetch.php?media=chemdata:nist17:nist17demo.zip], respectively.