Chemical models considering a gas kinetic temperature of T_k = 50 K and OPR = 1 × 10^-2 (from model A to model D). Models E and F consider a temperature T_k = 50 K, but their initial abundances are obtained using another model (with T_k = 15 K and OPR = 1 × 10^-4) at a time of 10⁵ yr (for model E) and 10⁶ yr (for model F). At the top part of the figures of every model, the red line represents the [HNC]/[HCN] ratio, the green represents the [DCN]/[HCN] ratio, the purple line shows the [DNC]/[HNC] ratio, and the blue line shows the [C₂D]/[C₂H] ratio. In the bottom part of the figures of every model, the blue line represents the [HDCO]/[H₂CO] ratio, the green line shows the [D₂CO]/[H₂CO] ratio, the purple line shows the [DCO⁺]/[HCO⁺] ratio, and the yellow one shows the [NH₂D]/[NH₃] ratio. The dashed lines shows the ratios of observational results toward MonR2 for the 10.5 km s^-1 component at the IF position.