We used the Arecibo Observatory, the most sensitive radio telescope, to conduct a spectral line survey, between 1 and 10 GHz, of the star forming region W51 IRS1, with the aim of obtaining a molecular line inventory in this frequency range. In this poster we present the results obtained from the C-Band frequency range (4 to 6 GHz). The data were taken with the Mock Spectrometer during the summers of 2010, 2011 and 2012, which provided simultaneous observations of 14 adjacent spectral windows, each with 8192 channels and a channel width of 7 kHz (~0.4 km/s in the C band). For most of the spectra we achieved an rms noise of about 4 mJy. So far, we have identified recombination lines of H, He, C and molecular lines of H2CO and H213CO. There are more lines detected which we still need to identify. Some possible candidate species include ethylene glycol g'Ga-(CH2OH)2.