Observations of molecular gas at 7 mm are made with the Green Bank Telescope (GBT) in a sample of planetary nebulae (PNe). PNe were selected to test stellar evolution models that include extra mixing processes induced by rotation by directly measuring the isotopic abundance ratios of processed material that has escaped the progenitor star. Moreover, these data are used to probe theories of chemical evolution through a sample of AGB stars, protoplanetary nebulae, and young and evolved PNe. One goal is to constrain the timelines and list of tracers for studying the molecular emission in these sources and examine the role of clumping for different species.