Observed data of TMC-1 from the QUIJOTE line survey (black histogram) and synthetic spectra calculated adopting as column density the upper limit given in the text (red curve). For each rotational transition, the most intense hyperfine components are shown. The abscissa corresponds to the rest frequency assuming a local standard of rest velocity of 5.83 km s⁻¹. The ordinate is the antenna temperature in millikelvin.