Appendix A: Spectroscopic Line Lists Spectroscopic line lists used in this work were retrieved from the CDMS database. Table A.1 summarizes the catalogs entries, molecular identifiers, and the primary laboratory or theoretical studies on which each entry is based. Table A.2, only available on Zenodo, lists spectroscopic parameters of all unblended or minimally blended transitions analyzed in this work, including rest frequencies, upper-state energies ($E_{\rm up}$), Einstein A-coefficients ($A_{\rm ij}$), and degeneracies ($g_{\rm up}$). Appendix B: Spectra of $syn$-$\rm HOCH_{2}C(O)NH_{2}$ observed at continuum peak towards G358.93-0.03 MM1 The observed spectra of GA toward the continuum peak of G358.93-0.03 MM1 are shown in Fig B.1 (available exclusively on Zenodo). Due to line blending effects, only three transitions are unblended or only slightly blended and were therefore used for quantitative analysis.