Modified Loomis-Wood diagram for the observed K_a = 0,1 lines of 2-cyanonaphthalene. The abscissa corresponds to the value of the rotational constant. The ordinate is the antenna temperature, corrected for atmospheric and telescope losses, in milli Kelvin. Each box presents the QUIJOTE data for frequencies 2 B_rotJ^*, where J^* = J_u + 1/2. The red line corresponds to the synthetic spectrum computed for TMC-1 including the rotational transitions of all molecular species detected in previous works and the two isomers of cyanonaphthalene and cyanoacenaphthylene. The rotational transitions of 2-cyanonaphthalene correspond to the lines connected through the blue vertical line (see text). For this isomer of cyanonaphthalene they correspond to the a-type transitions harmonically related with half integer quantum numbers, J^*, and corresponding to J_u = J⁺ − 1/2 and K_a = 0, 1.