Radial abundance profiles of the main C-, O- (left), and N-bearing (right) volatile molecules in the gas phase (dotted lines) and in the ice phase (solid lines) in the disc midplane after 3 Myr of chemical evolution without mass transport in the disc (stationary disc). The results are shown for the four chemical scenarios assuming a grain size of 0.1 μm. The horizontal small arrows indicate the initial abundances of H₂O, CO, CO₂, CH₃OH, CH₄, N₂, and NH₃ in the gas phase in the inheritance scenario (see also Table 2); note that CO and CO₂, as well as N₂ and NH₃, share the same initial abundance. The black profile (CRC), represents the cumulative abundance of additional carbon-rich compounds, including carbon chains, hydrocarbons, nitriles, and other complex organics that are not among the dominant volatile carriers.