  We present the discovery in TMC-1 of vinyl acetylene, CH2CHCCH, and the
detection, for the first time in a cold dark cloud, of HCCN, HC4N, and
CH3CH2CN. A tentative detection of CH3CH2CCH is also reported. The column
density of vinyl acetylene is (1.2 +/- 0.2)e13 cm-2, which makes it one of the
most abundant closed-shell hydrocarbons detected in TMC-1. Its abundance is
only three times lower than that of propylene, CH3CHCH2. The column densities
derived for HCCN and HC4N are (4.4 +/- 0.4)e11 cm-2 and (3.7 +/- 0.4)e11 cm-2,
respectively. Hence, the HCCN/HC4N abundance ratio is 1.2 +/- 0.3. For ethyl
cyanide we derive a column density of (1.1 +/- 0.3)e11 cm-2. These results are
compared with a state-of-the-art chemical model of TMC-1, which is able to
account for the observed abundances of these molecules through gas-phase
chemical routes.
