Synthesis of organic compounds in the circumstellar environment

Through the techniques of millimeter-wave and infrared spectroscopy, over 60 species of gas-phase molecules and a variety of inorganic and organic solids have been detected in the short phase of stellar evolution between the asymptotic giant branch and planetary nebulae. The chemical pathways that lead to the synthesis of complex organic compounds in such low-density environments are therefore important topics of astrochemistry. In this review, we summarize the observational evidence for the existence of complex aliphatic and aromatic compounds in these circumstellar environments, and discuss the nature of their possible carriers. Also discussed are a number of unidentified emission features which may also have an organic origin. The possible relations between these circumstellar organic matter with Solar System organic matter are explored.