Much like six-membered rings, five-membered rings are ubiquitous in organic chemistry, frequently serving as the building blocks for larger molecules, including many of biochemical importance. From a combination of laboratory rotational spectroscopy and a sensitive spectral line survey in the radio band toward the starless cloud core TMC-1, we report the astronomical detection of 1-cyano-1,3-cyclopentadiene (1-cyano-CPD, c-C₅H₅CN), a highly polar, cyano derivative of cyclopentadiene. The derived abundance of 1-cyano-CPD is far greater than predicted from astrochemical models that well reproduce the abundance of many carbon chains. This finding implies that either an important production mechanism or a large reservoir of aromatic material may need to be considered. The apparent absence of its closely related isomer, 2-cyano-1,3-cyclopentadiene, may arise from that isomer’s lower stability or may be indicative of a more selective pathway for formation of the 1-cyano isomer, perhaps one starting from acyclic precursors. The absence of N-heterocycles such as pyrrole and pyridine is discussed in light of the astronomical finding of 1-cyano-CPD.

就像六元环一样，五元环在有机化学中无处不在，经常充当更大分子的基础，包括许多生物化学重要性。通过结合实验室旋转光谱学和向无星云核心TMC-1进行无线电波段的敏感光谱线调查，我们报告了1-氰基-1,3-环戊二烯（1-cyano-CPD，cC ₅的天文检测高₅CN），一种高极性的环戊二烯氰基衍生物。1-氰基-CPD的衍生丰度远大于能很好地重现许多碳链丰度的天化学模型所预测的丰度。该发现暗示可能需要考虑重要的生产机理或大量的芳香族物质。其密切相关的异构体2-氰基-1,3-环戊二烯明显缺乏，可能是由于该异构体的较低稳定性所致，也可能表明形成1-氰基异构体的选择性更高，可能是从无环前体开始的。根据1-氰基-CPD的天文发现，讨论了不存在N-杂环如吡咯和吡啶。