The large cyanopolyyne compound cyanopentaacetylene (HC11N) was discovered in the late 1990s by
Bell et al., who detected it in
TMC-1 via two adjacent rotational transitions
measured in the laboratory with a
transform microwave spectrometer by
Travers et al. The observations were made with the
Green Bank telescope. Bell had previously claimed the
detection of HC11N in IRC +10216 in
1982 and in TMC-1 in
1985 on the basis of estimated rotational transition data
that proved to be inaccurate.
With its five C-C triple bonds, cyanopentaacetylene (also known as cyanodecapentayne or
following IUPAC naming guidelines for nitriles) is very unstable.
Nov 2016 - A new publication by
Loomis et al. concludes that the claimed detection of
HC11N by Bell et al. is not supported by their higher resolution observations.