Prediction of the relative abundance of cyclopentadiene (c-C₅H₆) as a function of time in the chemical model of TMC-1. The solid black line is the abundance predicted by the model without ion-molecule reactions, dashed lines represent how it is modified by including each of the reactions separately, and the solid green line is the total abundance when all the reactions from the dashed lines are included. The horizontal dotted line represents the observed abundance of cyclopentadiene in TMC-1, calculated from its column density (Cernicharo et al. 2021a).