Gas-phase C/O ratio as a function of distance from a solar-mass star for a disc characterised by α = 10⁻³. Red lines represent our fiducial model where all the refractory carbon is into refractory organics (χ_orga = 0.6 χ_tot,C, see Table A.1). Blue lines show the model where 20% of the refractory carbon is given to a new compound (T_sub > 1000 K) that does not sublimate within our disc boundary (such that χ_orga = 0.48 χ_tot,C). Finally, green lines show a model where the fraction of carbon removed from refractory organics is given to CO₂. The sublimation lines of the main species contributing to the C/O ratio are indicated with vertical lines.