  We report the detection, for the first time in space, of a new
non-functionalised hydrocarbon cycle in the direction of TMC-1: o-C6H4
(ortho-benzyne). We derive a column density for this hydrocarbon cycle of (5
+/- 1)e11 cm-2. The abundance of this species is around 30 times lower than
that of cyclopentadiene and indene. We compare the abundance of benzyne with
that of other pure hydrocarbons, cycles or chains, and find that it could be
formed from neutral-radical reactions such as C2H + CH2CHCCH and C + C5H5, and
possibly through C4H + C2H4, C3H + CH2CCH2, and C3H2 + C3H3. Hence, the rich
content of hydrocarbon cycles observed in TMC-1 could arise through a bottom-up
scenario involving reactions of a few radicals with the abundant hydrocarbons
recently revealed by the QUIJOTE line survey.
