Sketch of the physical model employed in this work. Left panel: collapse phase (see Sect. 3.1.1) solved in a single-zone approximation. The chemical output of phase I is used as initial condition of phase II. Central panel: warm-up phase solved in a 1D approximation from 1 to 10⁵ AU (see Sect. 3.1.2). Right panel: post-processing applied to compare the final chemical outputs of phase II with the column densities observed in the TOP100 (see Sects. 4.1 and 4.2). The physical parameters assumed in phases I and II are summarised in Table 1. The time evolution of the model is indicated by the dotted blue arrows.