Fractional abundance of C₂H for a representative set of chemical models discussed in Sect. 4 that account for the measured abundances of ethynyl in the SB ring and the outflow region of NGC 1068. The C₂H abundance is represented as a function of time for gas-grain chemical models (UCL_CHEM) number 13, 23, and 35, and as a function of distance for shock model number 46. This scale corresponds to the distance that the shock travels up to the dissipation length, which is the length scale over which the shock dissipates, beyond which the model is no longer applicable (see Jiménez-Serra et al. 2008). The main parameters of the models, extensively described in Sect. 4 and listed in Tables 4−6, are indicated in each panel. We highlight the range of C₂H abundances measured in the SB ring (≃a few 10^-8 for T_ex ≃ 10 K) and in the outflow region (≃a few 10^-7 for T_ex ≃ 25−50 K).