Cyanopolyyne

In organic chemistry, cyanopolyynes are a family of organic compounds with the chemical formula HC_nN (n = 3,5,7,…) and the structural formula H−[C≡C−]_nC≡N (n = 1,2,3,…). Structurally, they are polyynes with a cyano group (−C≡N) covalently bonded to one of the terminal acetylene units (H−C≡C).

A rarely seen group of molecules both due to the difficulty in production and the unstable nature of the paired groups, the cyanopolyynes have been observed as a major organic component in interstellar clouds.^[1] This is believed to be due to the hydrogen scarcity of some of these clouds. Interference with hydrogen is one of the reason for the molecule's instability due to the energetically favorable dissociation back into hydrogen cyanide and acetylene.^[2]

Cyanopolyynes were first discovered in interstellar molecular clouds in 1971 using millimeter wave and microwave telescopes.^[1] Since then many higher weight cyanopolyynes such as HC
₇N and HC
₁₁N have been discovered, although some of these identifications have been disputed. Other derivatives such as methylcyanoacetylene CH
₃C
₃N and ethylcyanoacetylene CH
₃CH
₂C
₃N have been observed as well.^[3] The simplest example is cyanoacetylene, H−C≡C−C≡N. Cyanoacetylene is more common on Earth and it is believed to be the initial reagent for most of the photocatalyzed formation of the interstellar cyanopolyynes. Cyanoacetylene is one of the molecules that was produced in the Miller–Urey experiment and is expected to be found in carbon-rich environments.^[4]

Identification is made through comparison of experimental spectrum with spectrum gathered from the telescope. This is commonly done with measurement of the rotational constant, the energy of the rotational transitions, or a measurement of the dissociation energy. These spectra can either be generated ab initio from a computational chemistry program or, such as with the more stable cyanoacetylene, by direct measurement of the spectra in an experiment. Once the spectra are generated, the telescope can scan within certain frequencies for the desired molecules. Quantification can be accomplished as well to determine the density of the compounds in the cloud.