Molecular Synthesis in the Circumstellar Environment by Dr. Sun Kwok (University of Calgary)   Recent observations by the Infrared Space Observatory (ISO) have found evidence of rapid synthesis of complex organic molecules in the late stages of stellar evolution. The chemical synthesis begins with the formation of acetylene, the first building block of benzene, in carbon stars. In a following proto-planetary nebulae stage, emission features corresponding to stretching and bending modes of aliphatic compounds are detected. When these objects evolve to become planetary nebulae, aromatic C-H and C-C stretching and bending modes become strong. These results show that complex carbonaceous compounds can be produced in a circumstellar environment over a period of only a few thousand years. In this talk, we will briefly describe the origin and evolution of planetary nebulae, the discovery of proto-planetary nebulae, the imaging of these objects by the Hubble Space Telescope, and a possible scenario of chemical evolution of organic material in the circumstellar environment.