  We report the detection of the oxygen-bearing complex organic molecules
propenal (C2H3CHO), vinyl alcohol (C2H3OH), methyl formate (HCOOCH3), and
dimethyl ether (CH3OCH3) toward the cyanopolyyne peak of the starless core
TMC-1. These molecules are detected through several emission lines in a deep
Q-band line survey of TMC-1 carried out with the Yebes 40m telescope. These
observations reveal that the cyanopolyyne peak of TMC-1, which is the prototype
of cold dark cloud rich in carbon chains, contains also O-bearing complex
organic molecules like HCOOCH3 and CH3OCH3, which have been previously seen in
a handful of cold interstellar clouds. In addition, this is the first secure
detection of C2H3OH in space and the first time that C2H3CHO and C2H3OH are
detected in a cold environment, adding new pieces in the puzzle of complex
organic molecules in cold sources. We derive column densities of (2.2 +/-
0.3)e11 cm-2, (2.5 +/- 0.5)e12 cm-2, (1.1 +/- 0.2)e12 cm-2, and (2.5 +/-
0.7)e12 cm-2 for C2H3CHO, C2H3OH, HCOOCH3, and CH3OCH3, respectively.
Interestingly, C2H3OH has an abundance similar to that of its well known isomer
acetaldehyde (CH3CHO), with C2H3OH/CH3CHO ~ 1 at the cyanopolyyne peak. We
discuss potential formation routes to these molecules and recognize that
further experimental, theoretical, and astronomical studies are needed to
elucidate the true mechanism of formation of these O-bearing complex organic
molecules in cold interstellar sources.
