Modified Loomis-Wood diagram of some of the observed lines of B429 (1-cyanoacenaphthylene). The abscissa corresponds to the value of the rotational constant, which has been fixed in this plot to values of between 429.040 and 429.160 MHz. The ordinate is the antenna temperature – corrected for atmospheric and telescope losses – in millikelvin. 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 with QUIJOTE, adopting for them the physical parameters derived in all previous works. This spectrum contains the rotational lines of the two isomers of cyanoacenaphtylene discovered in this paper. The rotational transitions of 1-cyanoacenaphthylene correspond to those connected through blue lines (see text). The blue line on the left side corresponds to the K_a = 0, 1 transitions that are harmonically related with half-integer quantum numbers.