Comparison of predicted and observed CH₃OH/CH₃CN abundance ratio versus CH₃OH/H₂ (see Fig. C.1 for other densities). Lines show model predictions at 300 (solid) and 1000 (dashed) yr after shock passage, with shaded areas representing intermediate times. Ratios are plotted for ζ_CR: 1 × 10⁻¹⁴ (green), 1 × 10⁻¹⁵ (cyan), and 1 × 10⁻¹⁶ (purple) s⁻¹. The orange band show the observed ratio (see Table 1), while the vertical grey line marks the CH₃OH abundance upper limit (Sect. 4).