CH₃CHO and NH₂CHO abundances (top panel) and their ratio (bottom panel) predicted by the gas-phase chemistry model that best represents our observations in L1157-B, including injection of formamide and acetaldehyde from the grains into the gas phase at the shock passage as labelled. As in Fig. 4, we indicate the physical parameter values, as well as the abundances of these molecules’ key reactants injected into the gas. Measurement points in B0, B1, and B2 are shown as crosses whose vertical lengths correspond to the measured abundance (ratio) uncertainties (see Table 2), and whose horizontal lengths account for a 500 yr uncertainty in the post-shock time as derived by Podio et al. (2016).