Envelopes around evolved stars are extraordinarily efficient factories of complex molecules and dust particles that will eventually enrich the ISM. To date, most chemistry studies have focused on C-rich envelopes, expected to show the largest molecular variety and abundances. Recent observations suggest that O-rich shells may be as chemically diverse as their Carbon counterparts, however, no serious attempt has been made yet to perform a full frequency scan of such objects. In this conference, I will report the first results from our spectral line surveys with the IRAM 30m telescope (~80-345 GHz) and Herschel/HIFI (~479-1244 GHz) of the well known, O-rich pre-PN OH 231.8+4.2 (a.k.a. The Rotten Egg nebula after the high abundance of Hydrogen sulfide, H2S, in its envelope). This object displays fast (>400 km/s), bipolar outflows and a molecular richness unparalleled amongst O-rich AGB and post-AGB stars. These surveys have led to the detection of hundreds of lines from different species, many of them detected for the first time in O-rich CSEs, that clearly confirm OH231.8+4.2 as the ''The Rosetta-stone'' for studying non-equilibrium, shock-induced molecule formation processes in O-rich environments. HIFI data have been particularly crucial to trace the physico-chemical conditions in the warm, dense circumstellar layers, which are not proved by lower-energy/frequency transitions. At these high frequencies, H2O and S-containing species are, together with CO, the dominant contributors to the total line flux observed. The main product from these surveys, is a molecular inventory and unprecentedly detailed chemical study (in progress) of an O-rich molecular flow accelerated by fast shocks.< Réduire